Aviation meteorology. Abstract of the lecture on the course “Aviation meteorology. Tashkent State Aviation Institute
Dangerous weather phenomena for aviation.
Phenomena that impair visibility
Fog ()- this is an accumulation of water droplets or crystals suspended in the air near the earth's surface, worsening horizontal visibility of less than 1000 m. At a visibility range of 1000 m to 10000 m, this phenomenon is called haze (=).
One of the conditions for the formation of fog in the surface layer is an increase in moisture content and a decrease in the temperature of moist air to the condensation temperature, the dew point.
Depending on what conditions influenced the formation process, several types of fogs are distinguished.
Intramass fogs
Radiation fogs are formed on clear, quiet nights due to radiative cooling of the underlying surface and cooling of the air layers adjacent to it. The thickness of such fogs ranges from a few meters to several hundred meters. Their density is greater near the ground, which means visibility is worse here, because. the lowest temperature is observed near the ground. With height, their density decreases and visibility improves. Such fogs form throughout the year in high pressure ridges, in the center of the anticyclone, in saddles:
First of all, they occur in lowlands, in ravines, in floodplains of rivers. As the sun rises and the wind increases, radiation fogs dissipate, and sometimes pass into a thin layer of low clouds. Radiation fogs are especially dangerous for aircraft landings.
Advective fogs are formed when a warm, moist air mass moves over the cold underlying surface of a continent or sea. They can be observed with a wind speed of 5 - 10 m/s. and more, occur at any time of the day, occupy large areas and persist for several days, creating serious interference for aviation. Their density increases with height and the sky is usually not visible. At temperatures from 0 to -10С, icing is observed in such fogs.
More often these fogs are observed in the cold half of the year in the warm sector of the cyclone and on the western periphery of the anticyclone.
In summer, advective fogs arise over the cold surface of the sea when air moves from warm land.
Advective radiation fogs are formed under the influence of two factors: the movement of warm air over the cold earth's surface and radiative cooling, which is most effective at night. These fogs can also occupy large areas, but are shorter in time than advective ones. Formed in the same synoptic situation as advective fogs (the warm sector of the cyclone, the western periphery of the anticyclone), they are most characteristic of the autumn-winter period.
mists slopes occur when moist air rises calmly along the slopes of mountains. The air then adiabatically expands and cools.
Mists of evaporation arise due to the evaporation of water vapor from a warm water surface into a colder surrounding
air. This is how evaporation fog appears over the Baltic and Black Seas, on the Angara River and in other places, when the water temperature is 8-10 ° C or more higher than the air temperature.
Frosty (stove) fogs are formed in winter at low temperatures in the regions of Siberia, the Arctic, as a rule, over small settlements (airfields) in the presence of surface inversion.
They usually form in the morning, when a large number of condensation nuclei begin to enter the air along with smoke from the furnace and stoves. They quickly acquire a significant density. During the day, when the air temperature rises, they collapse and weaken, but again increase in the evening. Sometimes such fogs are kept for several days.
Frontal fogsare formed in the zone of slowly moving and stationary fronts (warm and warm front of occlusion) at any (more often in the cold) time of day and year.
Prefrontal fogs are formed due to the saturation of cold air under the frontal surface with moisture. Conditions for the formation of pre-frontal fogs are created when the temperature of the falling rain is higher than the temperature of cold air located near the surface of the earth.
The fog formed during the passage of the front is a cloud system that has spread to the surface of the earth * This is especially often the case when the front passes over hills.
In terms of formation conditions, behind-frontal fog practically does not differ in any way from the conditions for the formation of advective fogs.
Blizzard - the transport of snow by strong winds over the surface of the earth. The intensity of a blizzard depends on wind speed, turbulence and snow conditions. A snowstorm can worsen visibility, make it difficult to land, and sometimes exclude the takeoff and landing of the aircraft. With strong prolonged snowstorms, the performance of airfields deteriorates.
There are three types of blizzards: drifting snow, blowing blizzard and general blizzard.
blowing snow() - snow transport by wind only at: the surface of the snow cover up to a height of 1.5 m. It is observed in the rear of the cyclone and the front of the anticyclone with a wind of 6 m / s. and more. He causes puffs on the strip, makes it hard visual definition distance to the ground. The horizontal visibility of snow does not worsen.
blowing snow() - the transfer of snow by the wind along the earth's surface with a rise to a height of more than "two meters. It is observed with a wind of 10-12 m / s or more. The synoptic situation is the same as during a snowstorm (the rear of the cyclone, the eastern periphery of the anticyclone). Visibility in a blowing snowstorm it depends on the wind speed If the wind is II-I4 m/s, then the horizontal visibility can be from 4 to 2 km, with a wind of 15-18 m/s - from 2 km up to 500 m and with wind more than 18 m/s. - less than 500 m.
General blizzard () - snowfall from clouds and at the same time being carried by the wind along the earth's surface. It usually starts with the wind 7 m/sec. and more. Occurs on atmospheric fronts. In height, it extends to the lower boundary of the clouds. In strong winds and heavy snowfall, it sharply worsens visibility both horizontally and vertically. Often during takeoff, landing in a general blizzard there is an electrization of the aircraft, distorting the readings of the instruments
Dust storm() - the transfer of large amounts of dust or sand by a strong wind. It is observed in deserts and places with an arid climate, but sometimes occurs in temperate latitudes. The horizontal extent of a dust storm may be. from several hundred meters to 1000 km. The vertical height of the atmospheric dust layer ranges from 1-2 km (dusty or sandy drifting snow) up to 6-9 km (dust storms).
The main reasons for the formation of dust storms are the turbulent structure of the wind that occurs during the daytime heating of the lower layers of air, the squally nature of the wind, and abrupt changes in the baric gradient.
The duration of a dust storm ranges from a few seconds to several days. Frontal dust storms present especially great difficulties in flight. As the front passes, the dust rises to great heights and is transported over a considerable distance.
mist() - clouding of the air caused by particles of dust and smoke suspended in it. With a strong degree of haze, visibility can decrease to hundreds and tens of meters. More often visibility at a haze of more than 1 km. It is observed in the steppes, in deserts: maybe after dust storms, forest and peat fires. haze over big cities associated with air pollution by smoke and dust of local origin. i
Aircraft icing.
The formation of ice on the surface of an aircraft when flying in supercooled clouds or fog is called icing.
Severe and moderate icing, in accordance with the GA PP, are among the meteorological phenomena dangerous for flights.
Even with light icing, the aerodynamic qualities of the aircraft change significantly, the weight increases, the engine power drops, the operation of control mechanisms and some navigation devices is disrupted. Ice thrown from icy surfaces can get into the engines or on the skin, which leads to mechanical damage. Icing on the cab windows impairs visibility, reduces the possibility of visibility.
The complex effect of icing on aircraft poses a threat to flight safety, and in some cases can lead to an aviation accident. Especially dangerous is icing during takeoff and landing as a concomitant phenomenon in case of failures. individual systems Sun.
The process of aircraft icing depends on many meteorological and aerodynamic variables. The main cause of icing is the freezing of supercooled water droplets when they collide with the aircraft. The manual for meteorological support of flights provides for a conditional gradation of the intensity of icing.
The intensity of icing is usually measured by the thickness of ice growth per unit time. Thickness is usually measured in millimeters of deposited ice on various parts VS per minute (mm/min.). When measuring the deposition of ice on the leading edge of the wing, it is customary to consider:
Weak icing - up to 0.5 mm / min;
Moderate - from 0.5 to 1.0 mm / min.;
Strong - more than 1.0 mm / min.
With a low degree of icing, the periodic use of anti-icing agents completely frees the aircraft from ice, but if the systems fail, flying in icing conditions is more than dangerous. A moderate degree is characterized by the fact that even a short-term entry of the aircraft into the icing zone without activated anti-icing systems is dangerous. With a strong degree of icing, the systems and means cannot cope with the growing ice and an immediate exit from the icing zone is necessary.
Aircraft icing occurs in clouds extending from ground to altitude 2-3 km. At negative temperatures, icing in water clouds is most likely. In mixed clouds, icing depends on the water content of their droplet-liquid part; in crystalline clouds, the probability of icing is low. Icing is almost always observed in intramass stratus and stratocumulus clouds at temperatures from 0 to -10°C.
In frontal cloudiness, the most intense icing of aircraft occurs in cumulonimbus clouds associated with cold fronts, occlusion fronts, and warm fronts.
In nimbostratus and altostratus clouds of a warm front, intense icing occurs if there is little or no precipitation, and with abundant precipitation on a warm front, the probability of icing is low.
The most intense icing can be observed when flying under clouds in a zone of supercooled rain and/or drizzle.
Icing is unlikely in the upper tier clouds, but it should be remembered that intense icing is possible in cirrostratus and cirrocumulus clouds if they remain after the destruction of thunderclouds.
Icing was possible at temperatures from -(-5 to -50 ° C in clouds, fog and precipitation. Statistics show that the largest number of cases of icing. Sun is observed at air temperatures from 0 to -20 ° C, and especially from - 10 ° C. Icing of gas turbine engines can also occur at positive temperatures from 0 to + 5 ° C.
Relationship between icing and precipitation
Supercooled rain is very dangerous with icing ( NS) Raindrops have a radius of a few mm, so even light supercooled rain can lead to heavy icing very quickly.
Drizzle (St ) at negative temperatures during a long flight, it also leads to severe icing.
Wet snow (NS , WITH B ) - usually falls out in flakes and is very dangerous with heavy icing.
Icing in "dry snow" or crystalline clouds is unlikely. However, icing of jet engines is possible even under such conditions - the surface of the air intake can be cooled to 0 °, snow, sliding along the walls of the air intake into the engine, can cause a sudden cessation of combustion in the jet engine.
Types and forms of aircraft icing.
The following parameters determine the type and form of aircraft icing:
Microphysical structure of clouds (whether they consist only of supercooled drops, only of crystals, or have; mixed structure, spectral size of drops, cloud water content, etc.);
- temperature of the flowing air flow;
- speed and mode of flight;
- shape and size of parts;
As a result of the impact of all these factors, the types and forms of ice deposition on the aircraft surface are extremely diverse.
The type of ice deposit is divided into:
Transparent or vitreous, most often formed when flying in clouds containing mainly large drops, or in a zone of supercooled rain at an air temperature of 0 to -10 ° C and below.
Large drops, hitting the surface of the aircraft, spread and gradually freeze, forming at first an even, ice film, which almost does not distort the profile of the bearing surfaces. With a significant increase, the ice becomes bumpy, which makes this type of deposit, which has the highest density, very dangerous due to the increase in weight and a significant change in the aerodynamic characteristics of the aircraft;
Opaque or mixed appears in mixed clouds at temperatures from -6 to -12 ° C. Large drops spread before freezing, small ones freeze without spreading, and snowflakes and crystals freeze into a film of supercooled water. As a result, translucent or opaque ice with uneven rough surface, the density of which is slightly less than transparent.This type of deposit strongly distorts the shape of the parts of the aircraft flown by the air flow, firmly adheres to its surface and reaches a large mass, therefore it is most dangerous;
White or coarse-grained, in small-drop clouds of stratus form and fog, it is formed at temperatures below -10 Drops quickly freeze when they hit the surface, retaining their shape. This type of ice is characterized by porosity and low specific gravity. Grainy ice has weak adhesion to aircraft surfaces and is easily separated by vibrations, but during a long flight in the icing zone, the accumulating ice under the influence of mechanical air shocks is compacted and acts like frosted ice;
Hoarfrost is formed when there are supercooled droplets in clouds with a large number of ice crystals at a temperature of -10 to -15°C. The hoarfrost deposit, uneven and rough, does not stick firmly to the surface and is easily thrown off by the air stream during vibration. Dangerous during a long flight in the icing zone, reaching a large thickness and having an uneven shape with torn protruding edges in the form of pyramids and columns;
Frost occurs as a result of sublimation of water vapor during the sudden entry of BC from cold layers into warm ones. It is a light fine-crystalline coating that disappears when the temperature of the aircraft equalizes with the air temperature. Hoarfrost: not dangerous, but can be a stimulant for severe icing when the aircraft enters the clouds.
The form of ice deposits depends on the same reasons as types:
- profile, having the appearance of the profile on which the ice was deposited; most often from transparent ice;
- wedge-shaped is a clip on the front cover of a product made of white coarse ice;
The grooved has a V reverse view on the leading edge of the streamlined profile. The recess is obtained due to kinetic heating and thawing of the central part. These are bumpy rough outgrowths of frosted ice. This is the most dangerous type of icing.
- barrier or mushroom-shaped - a roller or individual streaks behind the heating zone from transparent and frosted ice;
The shape largely depends on the profile, which varies along the entire length of the wing or propeller blade, so at the same time various forms icing.
Influence on icing of high speeds.
The influence of air speed on the intensity of icing affects in two ways:
An increase in speed leads to an increase in the number of droplets colliding with the surface of the aircraft”; and thereby increasing the intensity of icing;
As the speed increases, the temperature of the frontal parts of the aircraft increases. Kinetic heating appears, which affects the thermal conditions of the icing process and begins to manifest itself noticeably at speeds of more than 400 km / h
V km/h 400 500 600 700 800 900 1100
T С 4 7 10 13 17 21 22
Calculations show that the kinetic heating in clouds is 60% of the kinetic heating in dry air (heat loss for the evaporation of part of the droplets). In addition, kinetic heating is unevenly distributed over the surface of the aircraft and this leads to the formation dangerous form icing.
Type of ground icing.
On the surface of aircraft on the ground, at low temperatures, deposition can be observed various kinds ice. According to the conditions of formation, all types of ice are divided into three main groups.
The first group includes hoarfrost, hoarfrost and hard deposits, which are formed as a result of the direct transition of water vapor to ice (sublimation).
Frost covers mainly the upper horizontal surfaces of the aircraft when they are cooled to negative temperatures on clear, quiet nights.
Hoarfrost forms in moist air, mainly on the protruding windward parts of the aircraft, in frosty weather, fog and light winds.
Hoarfrost and hoarfrost adhere weakly to aircraft surfaces and are easily removed by mechanical treatment or hot water.
The second group includes types of ice formed when supercooled drops of rain or drizzle freeze. In the case of slight frosts (from 0 to -5°C), the falling raindrops spread over the surface of the aircraft and freeze in the form of transparent ice.
At lower temperatures, the droplets freeze quickly and frosted ice forms. These types of ice can reach large sizes and stick firmly to the surface of the aircraft.
The third group includes the types of ice deposited on the surface of the aircraft when freezing rain, sleet, fog drops. These types of ice do not differ in their structure from the types of ice of the second group.
Such types of aircraft icing on the ground sharply worsen its aerodynamic characteristics and increase its weight.
It follows from the above that the aircraft must be thoroughly cleared of ice before takeoff. Especially carefully you need to check the condition of the surface of the aircraft at night at negative air temperatures. It is forbidden to take off on an aircraft whose surface is covered with ice.
Helicopter icing features.
The physical and meteorological conditions of helicopter icing are similar to those of aircraft icing.
At temperatures from 0 to ~10°C, ice is deposited on the propeller blades mainly near the rotation axis and spreads to the middle. The ends of the blades are not covered with ice due to kinetic heating and high centrifugal force. At a constant number of revolutions, the intensity of icing of the propeller depends on the water content of the cloud or supercooled rain, the size of the droplets and the air temperature. At air temperatures below -10°C, the propeller blades are completely iced up, and the intensity of ice growth on the leading edge is proportional to the radius. When the main rotor is iced, a strong vibration occurs that disrupts the controllability of the helicopter, the engine speed drops, and the speed does not increase to the previous value. restores the lift of the propeller, which can lead to the loss of its instability.
Ice.
This layer of dense ice (opaque or transparent). growing on the surface of the earth and on objects when supercooled rain or drizzle falls. It is usually observed at temperatures from 0 to -5С, less often at lower temperatures: (up to -16 °). Ice is formed in the zone of a warm front, most often in the zone of an occlusion front, a stationary front, and in the warm sector of a cyclone.
Black ice - ice on the earth's surface, formed after a thaw or rain as a result of the onset of cooling, as well as ice remaining on the earth after the cessation of precipitation (after ice).
Flight operations in icing conditions.
Flights in icing conditions are permitted only on aircraft with a permit. In order to avoid the negative consequences of icing, during the pre-flight preparation period, it is necessary to carefully analyze the meteorological situation along the route and, based on the actual weather data and the forecast, determine the most favorable flight levels.
Before entering cloud cover, where icing is likely, anti-icing systems should be turned on, since a delay in switching on significantly reduces their efficiency.
With a strong degree of icing, anti-icing agents are not effective, therefore, in agreement with the traffic service, the flight level should be changed.
In winter, when the cloud layer with an isotherm from -10 to -12°С is located close to the earth's surface, it is advisable to go up to the temperature range below -20°С, giving the rest of the year, if the altitude reserve allows - down, to the area of positive temperatures.
If the icing has not disappeared during the change of flight level, it is necessary to return to the point of departure or land at the bluest alternate airfield.
Difficult situations most often arise due to pilots underestimating the danger of even light icing
THUNDERS
A thunderstorm is a complex atmospheric phenomenon in which multiple electrical discharges are observed, accompanied by a sound phenomenon - thunder, as well as rainfall.
Conditions necessary for the development of intramass thunderstorms:
air mass instability (large vertical temperature gradients, at least up to a height of about 2 km - 1/100 m before the condensation level and - > 0.5°/100m above the condensation level);
High absolute air humidity (13-15 mb. in the morning);
High temperatures at the earth's surface. The zero isotherm on days with thunderstorms lies at an altitude of 3-4 km.
Frontal and orographic thunderstorms develop mainly due to forced air rise. Therefore, these thunderstorms in the mountains begin earlier and end later, form on the windward side (if these are high mountain systems) and stronger than in flat terrain for the same synoptic position.
Development stages of a thundercloud.
The first is the growth stage, which is characterized by a rapid rise of the top and the preservation of the appearance of a droplet cloud. During this period, thermal convection transforms cumulus clouds (Cu) into powerful cumulus clouds (Cu conq/). In clouds b under the clouds, only ascending air movements from a few m/s (Cu) to 10-15 m/s (Cu conq/) are observed. Then the upper rug of the clouds passes into the zone of negative temperatures and acquires a crystalline structure. These are already cumulonimbus clouds and heavy rain begins to fall from them, downward movements appear above 0 ° - heavy icing.
Second - stationary stage , characterized by the cessation of the intensive growth of the top of the cloud upwards and the formation of an anvil (cirrus clouds, often elongated in the direction of the thunderstorm). These are cumulonimbus clouds at their peak. Turbulence is added to vertical movements. Upstream speeds can reach 63 m/s, downstream speeds ~ 24 m/s. In addition to heavy rains, there may be hail. At that time, electrical discharges are formed - lightning. Under the cloud there may be squalls, tornadoes. The upper boundary of the clouds reaches 10-12 km. In the tropics, individual peaks of thunderclouds develop to a height of 20-21 km.
The third is the stage of destruction (dissipation), in which the droplet-liquid part of the cumulonimbus cloud is washed out, and the top, which has turned into a cirrus cloud, often continues to exist independently. At this time, electrical discharges cease, precipitation weakens, and downward air movements predominate.
In the transitional seasons and in the winter period of the development stage, all the processes of a thundercloud are much less pronounced and do not always have clear visual signs.
According to RMO GA, a thunderstorm over an airfield is considered if the distance to the thunderstorm is No. km. and less. The thunderstorm is distant if the distance to the thunderstorm is more than 3 km.
For example: “09.55 distant thunderstorm in the northeast, moving to the southwest.”
“18.20 thunderstorm over the airfield.”
Phenomena associated with a thundercloud.
Lightning.
The period of electrical activity of a thundercloud is 30-40 minutes. The electrical structure of St is very complex and changes rapidly in time and space. Most of the observations of thunderclouds show that a positive charge is usually formed in the upper part of the cloud, a negative charge in the middle part, and both positive and negative charges can be present in the lower part. The radius of these areas with opposite charges varies from 0.5 km to 1-2 km.
Breakthrough tension electric field for dry air is I million w/m. In clouds, for the occurrence of lightning discharges, it is enough that the field strength reaches 300-350 thousand V/m. (measured values during experimental flights) Apparently, these or close to them values of the field strength represent the strength of the beginning of the discharge, and for its propagation, strengths much smaller, but covering a large area, are sufficient. The frequency of discharges in a moderate thunderstorm is about I per minute, and in an intense thunderstorm - 5–10 per minute.
Lightning- this is a visible electrical discharge in the form of curved lines, lasting a total of 0.5 - 0.6 seconds. The development of a discharge from a cloud begins with the formation of a stepped leader (streamer), which is advanced by "Jumps" 10-200m long. A return stroke develops from the earth's surface along the ionized lightning channel, which transfers the main lightning charge. The current strength reaches 200 thousand A. Usually after the first step leader through hundredths of a second. there is a development along the same channel of an arrow-shaped leader, after which a second return stroke takes place. This process can be repeated many times.
Line lightning are formed most often, their length is usually 2-3 km (between clouds can be up to 25 km), the average diameter is about 16 cm (maximum up to 40 cm), the path is zigzag.
Flat zipper- a discharge covering a significant part of the cloud and states of luminous quiet discharges emitted by individual droplets. Duration approx. 1 sec. You can not mix flat lightning with lightning. Zarnitsy are discharges of distant thunderstorms: lightning is not visible and thunder is not heard, only the illumination of clouds by lightning differs.
Ball lightning brightly glowing ball of white or reddish
colors with an orange tint and an average diameter of 10-20 cm. Appears after a linear lightning discharge; moves in the air slowly and silently, can penetrate buildings, aircraft during flight. Often, without causing harm, it quietly leaves, but sometimes it explodes with a deafening crash. The phenomenon can be milked from several seconds to several minutes. This is still a little studied physical and chemical process.
A lightning discharge into an aircraft can lead to depressurization of the cabin, fire, blinding of the crew, destruction of the skin, individual parts and radio equipment, magnetization of steel
cores in devices,
Thunder caused by heating and therefore expanding by the expansion of air along the lightning path. In addition, during the discharge, water molecules are decomposed into their constituent parts with the formation of "explosive gas" - "channel explosions". Since the sound from different points of the lightning path does not arrive at the same time and is repeatedly reflected from the clouds and the earth's surface, the thunder has the character of long peals. Thunder is usually heard at a distance of 15-20 km.
hail- this is precipitation falling from St in the form of spherical ice. If, above the 0° level, the maximum increase in updrafts exceeds 100 m/sec, and the top of the cloud is in the temperature zone of -20-25°, then ice may form in such a cloud. The hail focus is formed above the level of the maximum speed of ascending flows, and here the accumulation of large drops and the main growth of hailstones occur. In the upper part of the cloud, when crystals collide with supercooled drops, snow grains (hailstone nuclei) are formed, which, falling down, turn into hail in the zone of accumulation of large drops. The time interval between the beginning of the formation of hailstones in the cloud and their fall out of the cloud is about 15 min. The width of the "grad road" can be from 2 to 6 km, the length is 40-100 km. The thickness of the layer of fallen hail sometimes exceeds 20 cm. The average duration of hail fall is 5 10 min, but in some cases it can be more. Most often there are hailstones with a diameter of 1-3 cm, but they can be up to 10 cm or more. .Hail is found not only under the cloud, but can also damage the aircraft at high altitudes (up to an altitude of 13700 m and up to 15-20 km from a thunderstorm).
Hail can break the windows of the pilot's cabin, destroy the radome of the locator, pierce or make dents in the skin, damage the leading edge of the wings, stabilizer, and antennas.
heavy rain shower sharply reduces visibility to less than 1000 m, can cause engine shutdown, degrades the aerodynamic qualities of the aircraft and can, in some cases without any wind shear, reduce the applied force on approach or takeoff by 30%.
Squall- a sharp increase (more than 15 m / s) of the wind for several minutes, accompanied by a change in its direction. Wind speed during a squall often exceeds 20 m/s, reaching 30 and sometimes 40 m/s or more. The squall zone extends up to 10 km around the thundercloud, and if these are very powerful thunderstorm centers, then in the front part the width of the squall zone can reach 30 km. Dust swirls near the earth's surface in the region of a cumulonimbus cloud are a visual sign of an "air gust front" (squalls). Squalls are associated with intramass and frontal highly developed SW clouds.
squall gate- a vortex with a horizontal axis in front of the thundercloud. This is a dark, overhanging, swirling cloudy shaft 1-2 km before a continuous curtain of rain. Usually the whirlwind moves at a height of 500m, sometimes it drops to 50m. After its passage, a squall is formed; there may be a significant decrease in air temperature and an increase in pressure caused by the spread of air cooled by precipitation.
Tornado- a vertical vortex descending from a thundercloud to the ground. The tornado has the appearance of a dark cloud column several tens of meters in diameter. It descends in the form of a funnel, towards which another funnel of spray and dust can rise from the earth's surface, connecting with the first. Wind speeds in a tornado reach 50 - 100 m / s with a strong ascending component. The decrease in pressure inside the tornado can be 40-100 mb. Tornadoes can cause catastrophic destruction, sometimes with human casualties. The bypass of the tornado must be carried out at a distance of at least 30 km.
Turbulence near thunderclouds has a number of features. It becomes elevated already at a distance equal to the diameter of the thundercloud, and the closer to the cloud, the greater the intensity. As the cumulonimbus cloud develops, the turbulence zone increases, the greatest intensity is observed in the rear part. Even after the cloud has completely collapsed, the part of the atmosphere where it was located remains more perturbed, that is, turbulent zones live longer than the clouds with which they are associated.
Above the upper boundary of a growing cumulonimbus cloud, ascending movements at a speed of 7-10 m/s create a layer with intense turbulence 500 m thick. And above the anvil, descending air movements are observed, with a speed of 5-7 m / s, they lead to the formation of a layer with intense turbulence 200 m thick.
Types of thunderstorms.
Intramass thunderstorms formed over the continent. in summer and in the afternoon hours (over the sea, these phenomena are observed most often in winter and at night). Intra-mass thunderstorms are divided into:
- convective (thermal or local) thunderstorms, which are formed in low-gradient fields (in saddles, in old filling cyclones);
- advective- thunderstorms that form in the rear of the cyclone, because here there is an intrusion (advection) of cold air, which is very unstable in the lower half of the troposphere and thermal and dynamic turbulence develops well in it;
- orographic- are formed in mountainous areas, develop more often on the windward side and, at the same time, are stronger and more prolonged (begin earlier, end later) than in flat terrain under the same weather conditions on the windward side.
Frontal thunderstorms formed at any time of the day (depending on which front is located in the given area). In summer, almost all fronts (except stationary ones) produce thunderstorms.
Thunderstorm centers in the zone of fronts sometimes overlap zones up to 400-500 km long. On major slow moving fronts, thunderstorms can be masked by upper and middle clouds (especially on warm fronts). Very strong and dangerous thunderstorms form on the fronts of young deepening cyclones, at the top of the wave, at the point of occlusion. In the mountains, frontal thunderstorms, like frontal ones, intensify from the windward side. Fronts on the periphery of cyclones, old eroding fronts of occlusion, and surface fronts produce thunderstorms in the form of separate centers along the front, which, during aircraft flights, are bypassed in the same way as intramass ones.
In winter, thunderstorms in temperate latitudes rarely form, only in the zone of the main, active atmospheric fronts that separate air masses with a large temperature contrast and move at high speed.
Thunderstorms are being monitored visually and instrumentally. Visual observations have a number of disadvantages. A meteorological observer, whose observation radius is limited to 10-15 km, detects the presence of a thunderstorm. At night, in difficult meteorological conditions, it is difficult to determine the forms of clouds.
For instrumental observations of thunderstorms, meteorological radars (MRL-1, MRL-2, MRL-5), thunderstorm azimuth direction finders (PAT), panoramic thunderstorm recorders (PRG) and lightning detectors are used, which are part of the KRAMS complex (integrated radio automatic meteorological station) .
SCRL give the most full information on the development of thunderstorm activity within a radius of up to 300 km.
Based on the reflectivity data, it determines the location of the thunderstorm source, its horizontal and vertical dimensions, the speed and direction of displacement. Based on the observations, radar maps are compiled.
If thunderstorm activity is observed or forecast in the area of flights, during the period of pre-flight preparation, the KBC is obliged to carefully analyze the meteorological situation. Based on the SCRL maps, determine the location and direction of movement of thunderstorm (shower) sources, their upper boundary, outline avoidance routes, and a safe level conventions thunderstorms and heavy rainfall.
When approaching the zone of thunderstorm activity, the PIC should assess in advance the possibility of flying through this zone and inform the dispatcher about the condition of the flight. For safety, a decision is made to avoid thunderstorms or fly to an alternate airfield.
The controller, using the information of the meteorological service and weather reports from the aircraft, is obliged to inform the crews about the nature of thunderstorms, their vertical power, directions and speed of displacement, and give recommendations on leaving the area of thunderstorm activity.
When powerful cumulus and cumulonimbus clouds are detected in flight, it is allowed to bypass these clouds at a distance of at least 15 km from the nearest boundary of illumination.
The intersection of frontal clouds with individual thunderstorm centers can be carried out in the place where the distance between
borders of flare on the BRL screen at least 50 km ..
Flight over the upper boundary of the powerful cumulus and cumulonimbus opaques is allowed with an excess of at least 500 m above them.
Aircraft crews are prohibited from intentionally entering powerful cumulus and cumulonimbus clouds and areas of heavy rainfall.
When taking off, landing and in the presence of powerful cumulus, cumulonimbus clouds in the aerodrome area, the crew: is obliged to inspect the zone of the aerodrome area using the BRL, assess the possibility of takeoff, landing and determine the procedure for bypassing powerful cumulus, cumulonimbus clouds and areas of strong showers precipitation.
Flight under cumulonimbus clouds is allowed only during the day, outside the zone of heavy rainfall, if:
- aircraft flight altitude above the terrain is not less than 200 m and in mountainous terrain not less than 600 m;
- vertical distance from the aircraft to the lower boundary of the clouds is not less than 200 m.
Electrify the sun and discharge static electricity.
The phenomenon of aircraft electrification lies in the fact that when flying in clouds, precipitation due to friction (water drops, snowflakes), the surface of the aircraft receives an electric charge, the magnitude of which is the greater, the greater the aircraft and its speed, as well as the greater the number of moisture particles contained in unit volume of air. Charges on the aircraft can also appear when flying near clouds that have electric charges. The highest charge density is noted on the sharp convex parts of the aircraft, and the outflow of electricity in the form of sparks, luminous crowns, and a crown is observed.
Most often, aircraft electrization is observed when flying in crystalline clouds of the upper tier, as well as mixed clouds of the middle and lower tiers. The charge on the aircraft can also appear when flying near clouds that have electric charges.
In some cases, the electric charge that an aircraft has is one of the main causes of aircraft damage by lightning in nimbostratus clouds at altitudes of 1500 to 3000m. The greater the thickness of the clouds, the greater the likelihood of damage.
For the occurrence of electric discharges, it is necessary that an inhomogeneous electric field exist in the cloud, which is largely determined by the phase state of the cloud.
If the electric field strength between the bulk electric charges in the cloud is less than the critical value, then the discharge between them does not occur.
When flying near a cloud of an aircraft that has its own electric charge, the intensity fields can reach a critical value, then an electric discharge occurs in the aircraft.
As a rule, lightning does not occur in nimbostratus clouds, although they have oppositely named volumetric electric charges. The strength of the electric field is insufficient for the occurrence of lightning. But if near such a cloud or in it there is an aircraft with a large surface charge, then it can cause a discharge on itself. Lightning originating in the cloud will hit the BC.
The methodology for predicting dangerous damage to aircraft by electrostatic discharges outside the zones of active lightning activity has not yet been developed.
To ensure the safety of flight in nimbostratus clouds, in the event of a strong electrification of the aircraft, it is necessary to change the flight altitude in agreement with the controller.
Aircraft are damaged by atmospheric electric discharge more often in cloud systems of cold and secondary cold fronts, in autumn and winter more often than in spring and summer.
Signs of strong electrization of the aircraft are:
Noises and crackling in the headphones;
Random fluctuation of the arrows of the radio compass;
Sparking on the glass of the cockpit and the glow of the ends of the wings in the dark.
Atmospheric turbulence.
The turbulent state of the atmosphere is a state in which disordered vortex motions of various scales and different velocities are observed.
When crossing vortices, the aircraft is exposed to their vertical and horizontal components, which are separate gusts, as a result of which the balance of aerodynamic forces acting on the aircraft is disturbed. There are additional accelerations that cause the aircraft to chatter.
The main causes of air turbulence are temperature and wind speed contrasts arising for any reason.
When assessing the meteorological situation, it should be taken into account that turbulence can occur under the following conditions:
During takeoff and landing in the lower surface layer due to non-uniform heating of the earth's surface, flow friction on the earth's surface (thermal turbulence).
Such turbulence occurs during the warm period of the year and depends on the height of the sun, and the nature of the underlying surface, humidity and the nature of the stability of the atmosphere.
On a sunny summer day, the dry ones heat up the most. sandy soils, less - land areas covered with grass, forests, and even less - water surfaces. Unevenly heated land areas cause uneven heating of the air layers adjacent to the earth, and ascending movements that are uneven in intensity.
If the air is dry and stable, and the underlying surface is poor in moisture, then clouds do not form and in such areas there may be slight or moderate turbulence. It spreads from the ground to a height of 2500m. The maximum turbulence occurs in the afternoon hours.
If the air is humid, then with: ascending currents, clouds of cumulus forms are formed (especially with an unstable air mass). In this case, the cloud's tops are the upper limit of turbulence.
When crossing inversion layers in the tropopause zone and the inversion zone above the earth's surface.
On the boundary of such layers, in which the winds often have different directions and speeds, undulating motions arise, ..^ causing slight or moderate turbulence.
Turbulence of the same nature also occurs in the zone of frontal sections, where large contrasts in temperature and wind speed are observed:
- when flying in the jet stream zone due to the difference in velocity gradients;
When flying over mountainous area orographic turbulence is formed on the lee side of mountains and uplands. . . On the windward side, a uniform updraft is observed, and the higher the mountains and the less steep the slopes, the farther from the mountains the air rises. With a ridge height of 1000 m, ascending movements begin at a distance of 15 km from it, with a ridge height of 2500-3000 m at a distance of 60-80 km. If the windward slope is heated by the sun, then the speed of the updrafts increases due to the mountain-valley effect. But if the slopes are very steep and the wind is strong, vortices are also formed inside the updraft, and the flight will take place in the turbulence zone.
Directly above the very top of the ridge, the wind speed usually reaches its greatest value, especially in the layer 300-500m above the ridge, and there can be strong turbulence.
On the lee side of the ridge, the aircraft, falling into a powerful downdraft, will spontaneously lose altitude.
The influence of mountain ranges on air currents, under appropriate meteorological conditions, extends to high altitudes.
When the air stream crosses a mountain range, lee waves are formed. They are formed when:
- if the air flow is perpendicular to the mountain range and the speed of this flow at the top is 50 km/h. and more;
- if the wind speed increases with height:
If the transshipment air is rich in moisture, then in the part where ascending air currents are observed, lentil-shaped clouds form.
In the case when dry air passes over the mountain range, cloudless lee waves are formed and the pilot may quite unexpectedly encounter a strong turbulence (one of the cases of TYN).
In zones of convergence and divergence of air flows with a sharp change in flow in direction.
In the absence of clouds, these will be the conditions for the formation of CAT (clear sky turbulence).
The horizontal extent of the TYAN can be several hundred kilometers. a
several hundred meters thick. hundreds of meters. Moreover, there is such a dependence, the more intense the turbulence (and the associated turbulence BC), the smaller the layer thickness.
When preparing for a flight, according to the isohypse configuration on the AT-400, AT-300 maps, it is possible to determine the zones of possible aircraft turbulence.
Wind shear.
Wind shear - a change in the direction and (or) speed of the wind in space, including ascending and descending air currents.
Depending on the orientation of points in space and the direction of aircraft movement relative to V1Sh, vertical and horizontal wind shears are distinguished.
The essence of the effect of wind shear is that with an increase in the mass of the aircraft (50-200t), the aircraft began to have greater inertia, which prevents a rapid change in ground speed, while its indicated speed changes according to the speed of the air flow.
The greatest hazard is wind shear when the aircraft is on the glide path in the landing configuration.
Criteria for wind shear intensity (recommended by working group
(ICAO).
| Wind shear intensity - a qualitative term | Vertical wind shear - updraft and downdraft at 30 m altitude, horizontal wind shear at 600 m, m/s. | Impact on aircraft control |
| Weak | 0 - 2 | Minor |
| Moderate | 2 – 4 | Significant |
| Strong | 4 – 6 | dangerous |
| Very strong | More than 6 | dangerous |
Many AMSGs do not have continuous wind data (for any 30m layer) in the surface layer, so the wind shear values are recalculated for the 100m layer:
0-6 m/s - weak; 6 -13 m/sec. - moderate; 13 -20 m/s, strong
20 m/s very strong
Horizontal (lateral) wind shear due to. a sharp change in wind direction with height, cause a tendency to shift the aircraft from the center line of the OHSS. When landing an aircraft, this is a call ^ eliminates the danger of touching the ground near the runway, during takeoff, the layout
increase the lateral offset beyond the safe climb sector.
Vertsh
Vertical wind shear in the 
With a sharp increase in wind with "height, a positive wind shear occurs.
Meteorology is a science that studies the physical processes and phenomena occurring in the earth's atmosphere, in their continuous connection and interaction with the underlying surface of the sea and land.
Aviation meteorology is an applied branch of meteorology that studies the influence of meteorological elements and weather phenomena on aviation activities.
Atmosphere. The air layer of the earth is called the atmosphere.
By the nature of the temperature distribution along the vertical, the atmosphere is usually divided into four main spheres: troposphere, stratosphere, mesosphere, thermosphere and three transitional layers between them: tropopause, stratopause and mesopause (6).
Troposphere - the lower layer of the atmosphere, the height is 7-10 km at the poles and up to 16-18 km in the equatorial regions. All weather phenomena develop mainly in the troposphere. In the troposphere, clouds form, fogs, thunderstorms, snowstorms occur, aircraft icing and other phenomena are observed. The temperature in this layer of the atmosphere drops with height by an average of 6.5 ° C every kilometer (0.65 ° C for 100%).
The tropopause is the transitional layer that separates the troposphere from the stratosphere. The thickness of this layer ranges from several hundred meters to several kilometers.
Stratosphere - the layer of the atmosphere that lies above the troposphere, up to a height of approximately 35 km. The vertical movement of air in the stratosphere (compared to the troposphere) is very weak or almost absent. The stratosphere is characterized by a slight decrease in temperature in the 11-25 km layer and an increase in the 25-35 km layer.
The stratopause is the transitional layer between the stratosphere and the mesosphere.
The mesosphere is a layer of the atmosphere that extends from about 35 to 80 km. Characteristic of the mesosphere layer is a sharp increase in temperature from the beginning to the level of 50-55 km and its decrease to the level of 80 km.
The mesopause is the transitional layer between the mesosphere and the thermosphere.
Thermosphere - the layer of the atmosphere above 80 km. This layer is characterized by a continuous sharp increase in temperature with height. At an altitude of 120 km, the temperature reaches +60°C, and at an altitude of 150 km -700°C.
A diagram of the structure of the atmosphere up to a height of 100 km is presented.
The standard atmosphere is a conditional distribution along the height of the average values of the physical parameters of the atmosphere (pressure, temperature, humidity, etc.). The following conditions are accepted for the international standard atmosphere:
- pressure at sea level, equal to 760 mm Hg. Art. (1013.2 mb);
- relative humidity 0%; temperature at sea level -f 15 ° C and falling with height in the troposphere (up to 11,000 m) by 0.65 ° C for every 100 m.
- above 11,000 m, the temperature is assumed to be constant and equal to -56.5 ° C.
See also:
METEOROLOGICAL ELEMENTS
The state of the atmosphere and the processes occurring in it are characterized by a number of meteorological elements: pressure, temperature, visibility, humidity, clouds, precipitation and wind.
Atmospheric pressure is measured in millimeters of mercury or millibars (1 mm Hg - 1.3332 mb). Atmospheric pressure equal to 760 mm is taken as normal pressure. rt. Art., which corresponds to 1013.25 mb. Normal pressure is close to the mean pressure at sea level. Pressure is constantly changing both near the surface of the earth and at heights. The change in pressure with height can be characterized by the value of the barometric step (the height to which one must rise or fall in order for the pressure to change by 1 mm Hg, or 1 mb).
The value of the barometric step is determined by the formula
Air temperature characterizes the thermal state of the atmosphere. Temperature is measured in degrees. The change in temperature depends on the amount of heat coming from the Sun at a given geographical latitude, the nature of the underlying surface and atmospheric circulation.
In the USSR and most other countries of the world, a centigrade scale is adopted. For the main (reference) points in this scale are taken: 0 ° C - the melting point of ice and 100 ° C - the boiling point of water at normal pressure(760 mm Hg). The gap between these points is divided into 100 equal parts. This interval is called "one degree Celsius" - 1 ° C.
Visibility. Under the range of horizontal visibility near the ground, determined by meteorologists, is understood the distance at which it is still possible to detect an object (landmark) in shape, color, brightness. Visibility is measured in meters or kilometers.
Air humidity - the content of water vapor in the air, expressed in absolute or relative units.
Absolute humidity is the amount of water vapor in grams per liter of air.
Specific humidity - the amount of water vapor in grams per 1 kg of moist air.
Relative humidity is the ratio of the amount of water vapor contained in the air to the amount required to saturate the air at a given temperature, expressed as a percentage. From the value of relative humidity, it can be determined how close a given state of humidity is to saturation.
The dew point is the temperature at which air would reach saturation at a given moisture content and constant pressure.
The difference between the air temperature and the dew point is called the dew point deficit. The dew point is equal to the air temperature if its relative humidity is 100%. Under these conditions, water vapor condenses and clouds and fogs form.
Clouds are accumulations of water droplets or ice crystals suspended in the air, resulting from the condensation of water vapor. When observing clouds, their number, shape and height of the lower boundary are noted.
The number of clouds is estimated on a 10-point scale: 0 points means no clouds, 3 points - three-quarters of the sky is covered with clouds, 5 points - half of the sky is covered with clouds, 10 points - the entire sky is covered with clouds (overcast). The height of the clouds is measured using spotlights, searchlights, pilot balloons and airplanes.
All clouds, depending on the location of the height of the lower boundary, are divided into three tiers:
The upper tier is above 6000 m, it includes: cirrus, cirrocumulus, cirrostratus.
The middle tier is from 2000 to 6000 m, it includes: altocumulus, altostratus.
The lower tier is below 2000 m, it includes: stratocumulus, stratus, stratocumulus. The lower tier also includes clouds that extend at a considerable distance along the vertical, but whose lower boundary lies in the lower tier. These clouds include cumulus and cumulonimbus. These clouds stand out in a special group of clouds of vertical development. Cloud cover has the greatest impact on aviation activity, as precipitation, thunderstorms, icing and heavy turbulence are associated with clouds.
Precipitation is water droplets or ice crystals that fall from clouds onto the surface of the earth. According to the nature of the precipitation, precipitation is divided into overhead, falling from stratified nimbus and altostratus clouds in the form of raindrops. medium size or in the form of snowflakes; showers falling from cumulonimbus clouds in the form of large drops of rain, snow flakes or hail; drizzle falling from stratus and stratocumulus clouds in the form of very fine raindrops.
Flight in the precipitation zone is difficult due to a sharp deterioration in visibility, a decrease in the height of clouds, turbidity, icing in supercooled rain and drizzle, and possible damage to the surface of an aircraft (helicopter) when hail falls.
Wind is the movement of air relative to the earth's surface. Wind is characterized by two quantities: speed and direction. The unit of wind speed is meter per second (1 m/sec) or kilometer per hour (1 km/h). 1 m/s = = 3.6 km/h.
The direction of the wind is measured in degrees, and it should be taken into account that the countdown is from the North Pole clockwise: the north direction corresponds to 0 ° (or 360 °), the east - 90 °, the south - 180 °, the west - 270 °.
The direction of the meteorological wind (where it blows) differs from the direction of the aeronautical wind (where it blows) by 180 °. In the troposphere, the wind speed increases with height and reaches a maximum below the tropopause.
Relatively narrow zones of strong winds (speeds of 100 km/h and above) in the upper troposphere and lower stratosphere at altitudes close to the tropopause are called jet streams. The part of the jet stream where the wind speed reaches its maximum value is called the axis of the jet stream.
The jet streams span thousands of kilometers in length, hundreds of kilometers in width, and several kilometers in height.
"PRACTICAL AERONAUTICAL METEOROLOGY Tutorial for the flight and dispatching staff of civil aviation Compiled by the teacher of the Ural training center of civil aviation Pozdnyakova V.A. Yekaterinburg 2010 ... "
-- [ Page 1 ] --
Ural UTC GA
PRACTICAL AVIATION
METEOROLOGY
Training manual for the flight and air traffic controllers of civil aviation
Compiled by the teacher of the Ural UTC GA
Pozdnyakova V.A.
Yekaterinburg 2010
pages
1 Structure of the atmosphere 4
1.1 Atmospheric research methods 5
1.2 Standard atmosphere 5-6 2 Meteorological quantities
2.1 Air temperature 6-7
2.2 Air density 7
2.3 Humidity 8
2.4 Atmospheric pressure 8-9
2.5 Wind 9
2.6 Local winds 10 3 Vertical air movements
3.1 Causes and types of vertical air movements 11 4 Clouds and precipitation
4.1 Reasons for the formation of clouds. Cloud classification 12-13
4.2 Cloud observations 13
4.3 Precipitation 14 5 Visibility 14-15 6 Atmospheric processes that determine the weather 16
6.1 Air masses 16-17
6.2 Weather fronts 18
6.3 Warm front 18-19
6.4 Cold front 19-20
6.5 Occlusion fronts 20-21
6.6 Secondary edges 22
6.7 Upper warm front 22
6.8 Stationary fronts 22 7 Baric systems
7.1 Cyclone 23
7.2 Anticyclone 24
7.3 Movement and evolution of baric systems 25-26
8. High-rise frontal zones 26
– – –
INTRODUCTION
Meteorology is the science of the physical state of the atmosphere and the phenomena occurring in it.Aviation meteorology studies meteorological elements and atmospheric processes from the point of view of their influence on aviation activities, and also develops methods and forms of meteorological support for flights.
Aircraft flights without meteorological information are impossible. This rule applies to all aircraft and helicopters without exception in all countries of the world, regardless of the length of the routes. All flights of civil aviation aircraft can be carried out only if the flight crew is aware of the meteorological situation in the flight area, landing point and alternate airfields. Therefore, it is necessary that each pilot has a perfect command of the necessary meteorological knowledge, understands the physical essence of meteorological phenomena, their connection with the development of synoptic processes and local physical and geographical conditions, which is the key to flight safety.
The proposed training manual in a concise and accessible form sets out the concepts of the main meteorological quantities, phenomena, in connection with their impact on the work of aviation. The meteorological conditions of the flight are considered and practical recommendations are given on the most expedient actions of the flight crew in a difficult meteorological situation.
1. The structure of the atmosphere The atmosphere is divided into several layers or spheres that differ in physical properties. The difference between the layers of the atmosphere is most clearly manifested in the nature of the distribution of air temperature with height. On this basis, five main spheres are distinguished: troposphere, stratosphere, mesosphere, thermosphere and exosphere.
Troposphere - extends from the earth's surface to a height of 10-12 km in temperate latitudes. At the poles it is lower, at the equator it is higher. About 79% of the total mass of the atmosphere and almost all of the water vapor is concentrated in the troposphere. Here, a decrease in temperature with height is observed, vertical air movements take place, westerly winds, clouds and precipitation are formed.
There are three layers in the troposphere:
a) Boundary (friction layer) - from the ground to 1000-1500 m. This layer affects the thermal and mechanical effects of the earth's surface. The daily variation of meteorological elements is observed. The lower part of the boundary layer up to 600 m thick is called the "surface layer". Here, the influence of the earth's surface is most pronounced, as a result of which such meteorological elements as temperature, air humidity, and wind experience drastic changes with height.
The nature of the underlying surface largely determines the weather conditions of the surface layer.
b) The middle layer is located from upper bound boundary layer and extends to a height of 6 km. In this layer, the influence of the earth's surface almost does not affect. Here, weather conditions are determined mainly by atmospheric fronts and vertical convective air currents.
c) The upper layer lies above the middle layer and extends to the tropopause.
The tropopause is a transitional layer between the troposphere and the stratosphere with a thickness of several hundred meters to 1-2 km. The lower boundary of the tropopause is taken to be the height where the drop in temperature with height is replaced by an even course of temperature, an increase or slowdown in the fall with height.
When crossing the tropopause at flight level, a change in temperature, moisture content and air transparency can be observed. The maximum wind speed is usually located in the tropopause zone or under its lower boundary.
The height of the tropopause depends on the temperature of the tropospheric air, i.e. from the latitude of the place, the time of year, the nature of synoptic processes (in warm air it is higher, in cold air it is lower).
The stratosphere extends from the tropopause to an altitude of 50-55 km. The temperature in the stratosphere rises and approaches 0 degrees at the upper boundary of the stratosphere. It contains about 20% of the total mass of the atmosphere. Due to the low content of water vapor in the stratosphere, clouds do not form, with the rare exception of occasional mother-of-pearl clouds, consisting of the smallest supercooled water droplets. The winds are predominantly western, in summer above 20 km there is a transition to eastern winds. The tops of cumulonimbus clouds can penetrate into the lower layers of the troposphere from the upper troposphere.
Above the stratosphere lies an air layer - the stratopause, which separates the stratosphere from the mesosphere.
The mesosphere is located from a height of 50-55 km and extends to a height of 80-90 km.
The temperature here decreases with height and reaches values of about -90°.
The transition layer between the mesosphere and the thermosphere is the mesopause.
The thermosphere occupies heights from 80 to 450 km. According to indirect data and the results of rocket observations, the temperature here increases sharply with height and at the upper boundary of the thermosphere it can be 700°-800°.
The exosphere is the outer layer of the atmosphere over 450 km.
1.1 Atmospheric research methods Direct and indirect methods are used to study the atmosphere. Direct methods include, for example, meteorological observations, radio sounding of the atmosphere, radar observations. Meteorological rockets and artificial satellites Lands equipped with special equipment.
In addition to direct methods, indirect methods based on the study of geophysical phenomena occurring in the high layers of the atmosphere provide valuable information on the state of the high layers of the atmosphere.
Laboratory experiments and mathematical modeling are carried out (a system of formulas and equations that allow obtaining numerical and graphic information about the state of the atmosphere).
1.2.Standard atmosphere Movement aircraft in the atmosphere is accompanied by a complex interaction with the environment. The physical state of the atmosphere determines the aerodynamic forces arising in flight, the thrust force created by the engine, fuel consumption, speed and maximum allowable flight altitude, readings of aeronautical instruments (barometric altimeter, speed indicator, M number indicator), etc.
The real atmosphere is very variable, therefore, for the design, testing and operation of an aircraft, the concept of a standard atmosphere has been introduced. SA is the estimated vertical distribution of temperature, pressure, air density and other geophysical characteristics, which, by international agreement, represents the average annual and mid-latitude state of the atmosphere. The main parameters of the standard atmosphere:
The atmosphere at all altitudes consists of dry air;
For zero height ("earth"), the mean sea level is taken, at which the air pressure is 760 mm Hg. Art. or 1013.25 hPa.
Temperature +15°C
Air density is 1.225kg/m2;
The boundary of the troposphere is considered to lie at an altitude of 11 km; the vertical temperature gradient is constant and equal to 0.65°C per 100m;
In the stratosphere, i.e. above 11km, the temperature is constant and equal to -56.5°C.
2. Meteorological quantities
2.1 Air temperature Atmospheric air is a mixture of gases. The molecules in this mixture are in continuous motion. Each state of the gas corresponds to a certain speed of movement of molecules. The higher the average speed of the molecules, the higher the air temperature. Temperature characterizes the degree of air heating.
The following scales are adopted for the quantitative characteristics of temperature:
The centigrade scale is the Celsius scale. On this scale, 0°C corresponds to the melting point of ice, 100°C to the boiling point of water, at a pressure of 760 mm Hg.
Fahrenheit. For the lower temperature of this scale, the temperature of the mixture of ice with ammonia (-17.8 ° C) is taken; for the upper temperature, the temperature of the human body. The gap is divided into 96 parts. T°(C)=5/9 (T°(F) -32).
In theoretical meteorology, it is used absolute scale- Kelvin scale.
The zero of this scale corresponds to the complete cessation of the thermal motion of molecules, i.e. lowest possible temperature. T°(K)= T°(C)+273°.
The transfer of heat from the earth's surface to the atmosphere is carried out by the following main processes: thermal convection, turbulence, radiation.
1) Thermal convection is a vertical rise of air heated over certain parts of the earth's surface. The strongest development of thermal convection is observed in the daytime (afternoon) hours. Thermal convection can propagate to the upper boundary of the troposphere, carrying out heat exchange throughout the entire thickness of the tropospheric air.
2) Turbulence is a countless number of small whirlwinds (from the Latin turbo whirlpool, whirlpool) that occur in a moving air stream due to its friction on the earth's surface and the internal friction of particles.
Turbulence contributes to the mixing of air, and hence the exchange of heat between the lower (heated) and upper (cold) layers of air. Turbulent heat exchange is mainly observed in the surface layer up to a height of 1-1.5 km.
3) Radiation is the return of the heat received by the earth's surface as a result of the influx of solar radiation. Heat rays are absorbed by the atmosphere, resulting in an increase in air temperature and cooling of the earth's surface. The radiated heat heats the ground air, and the earth's surface, due to heat loss, cools. The radiation process takes place at night, and in winter it can be observed throughout the day.
Of the three main processes of heat transfer from the earth's surface to the atmosphere considered, thermal convection and turbulence play the main role.
The temperature can change both horizontally along the earth's surface and vertically upwards. The value of the horizontal temperature gradient is expressed in degrees over a certain distance (111 km or 1° meridian). the activity of the atmospheric front increases.
The value that characterizes the change in air temperature with height is called the vertical temperature gradient, its value is variable and depends on the time of day, year, and the nature of the weather. According to ISA, y \u003d 0.65 ° / 100 m.
The layers of the atmosphere in which there is an increase in temperature with a height (y0 ° C) are called inversion layers.
Layers of air in which the temperature does not change with height are called layers of isotherm (y = 0 ° C). They are delay layers: they dampen vertical air movements, under them there is an accumulation of water vapor and solid particles that impair visibility, fogs and low clouds form. Inversions and isotherms can lead to significant vertical stratification of flows and the formation of significant vertical meter shifts, which cause aircraft turbulence and affect the flight dynamics during landing approach or takeoff.
Air temperature affects the flight of an aircraft. Aircraft takeoff and landing data largely depend on temperature. The length of the takeoff run and takeoff distance, the length of the run and landing distance decreases with decreasing temperature. The air density depends on the temperature, which determines the regime characteristics of the aircraft flight. As the temperature rises, the density decreases, and, consequently, the velocity head decreases and vice versa.
A change in velocity pressure causes a change in engine thrust, lift, drag, horizontal and vertical speed. Air temperature affects flight altitude. So increasing it at high altitudes by 10 ° from the standard one leads to a decrease in the ceiling of the aircraft by 400-500 m.
The temperature is taken into account when calculating the safe flight altitude. Very low temperatures complicate the operation of aviation equipment. At air temperatures close to 0 ° C and below, with supercooled precipitation, ice is formed, while flying in clouds - icing. Temperature changes of more than 2.5°C per 100 km cause atmospheric turbulence.
2.2 Air density Air density is the ratio of the mass of air to the volume it occupies.
The air density determines the regime characteristics of the aircraft flight. Velocity is dependent on air density. The larger it is, the greater is the velocity head and, consequently, the greater is the aerodynamic force. The density of air, in turn, depends on temperature and pressure. From the Clapeyron-Mendeleev equation of state for an ideal gas P Density in-ha = ------, where R is the gas constant.
RT P-air pressure T- gas temperature.
As can be seen from the formula, as the temperature increases, the density decreases, and consequently, the velocity head decreases. As the temperature decreases, the opposite is observed.
A change in velocity head causes a change in engine thrust, lift, drag, and hence the horizontal and vertical speeds of the aircraft.
The length of the run and landing distance is inversely proportional to the density of the air and, consequently, to the temperature. A decrease in temperature by 15°C reduces the length of the run and takeoff distance by 5%.
An increase in air temperature at high altitudes by 10° leads to a decrease in the practical ceiling of the aircraft by 400-500 m.
2.3 Air humidity Air humidity is determined by the amount of water vapor in the atmosphere and is expressed using the following basic characteristics.
Absolute humidity is the amount of water vapor in grams contained in I m3 of air. The higher the air temperature, the greater the absolute humidity. It is used to judge the occurrence of clouds of vertical development, thunderstorm activity.
Relative humidity - is characterized by the degree of saturation of the air with water vapor. Relative humidity is the percentage of the actual amount of water vapor contained in the air to the amount needed to be completely saturated at a given temperature. At a relative humidity of 20-40%, the air is considered dry, at 80-100% - humid, at 50-70% - air of moderate humidity. With an increase in relative humidity, there is a decrease in cloudiness, deterioration of visibility.
The dew point temperature is the temperature at which water vapor in the air reaches saturation at a given moisture content and constant pressure. The difference between the actual temperature and the dew point temperature is called the dew point deficit. The deficit shows how many degrees it is necessary to cool the air so that the vapor contained in it reaches a state of saturation. With dew point deficits of 3-4° or less, the air mass near the ground is considered humid, and fogs often occur at 0-1°.
The main process leading to the saturation of air with water vapor is a decrease in temperature. Water vapor plays an important role in atmospheric processes. It strongly absorbs thermal radiation, which is emitted by the earth's surface and atmosphere, and thereby reduces the loss of heat from our planet. The main effect of humidity on the operation of aviation is through cloudiness, precipitation, fog, thunderstorms, and icing.
2.4 Atmospheric pressure Atmospheric air pressure is the force acting on a unit of horizontal surface in 1 cm2 and equal to the weight of the air column extending through the entire atmosphere. The change in pressure in space is closely related to the development of the main atmospheric processes. In particular, horizontal pressure inhomogeneity is the cause of air currents. The value of atmospheric pressure is measured in mm Hg.
millibars and hectopascals. There is a dependency between them:
– – –
1 mmHg \u003d 1.33 mb \u003d 1.33 hPa 760 mm Hg. = 1013.25 hPa.
The change in pressure in the horizontal plane per unit of distance (1 ° of the meridian arc (111 km) or 100 km is taken per unit of distance) is called the horizontal baric gradient. It is always directed to the side. low pressure. The wind speed depends on the magnitude of the horizontal baric gradient, and the direction of the wind depends on its direction. In the northern hemisphere, the wind blows at an angle to the horizontal baric gradient, so that if you stand with your back to the wind, then low pressure will be to the left and somewhat ahead, and high pressure will be to the right and somewhat behind the observer.
For a visual representation of the distribution of atmospheric pressure, lines are drawn on weather maps - isobars connecting points with the same pressure. Isobars distinguish baric systems on maps: cyclones, anticyclones, troughs, ridges and saddles. Changes in pressure at any point in space over a period of time of 3 hours are called the baric trend, its value is plotted on surface synoptic weather maps, on which lines of equal baric trends are drawn - isallobars.
Atmospheric pressure decreases with height. In flight operations and flight management, it is necessary to know the change in altitude depending on the vertical pressure change.
This value is characterized by a baric step - which determines the height to which one must rise or fall in order for the pressure to change by 1 mm Hg. or 1 hPa. It is equal to 11 m per 1 mm Hg, or 8 m per 1 hPa. At a height of 10 km, the step is 31 m with a change in pressure of 1 mm Hg.
To ensure flight safety, air pressure is transmitted to crews in the weather, reduced to the threshold level of the runway for a working start in mm Hg, mb, or pressure reduced to sea level for a standard atmosphere, depending on the type of aircraft.
The barometric altimeter on an aircraft is based on the principle of measuring altitude by pressure. Since in flight the flight altitude is maintained according to the barometric altimeter, i.e. flight occurs at a constant pressure, then in fact the flight is carried out on an isobaric surface. The uneven occurrence of isobaric surfaces in height leads to the fact that the true flight altitude can differ significantly from the instrumental one.
So, above the cyclone, it will be below the instrumental one and vice versa. This should be taken into account when determining the safe level and when flying at altitudes close to the ceiling of the aircraft.
2.5 Wind There is always horizontal movement of air in the atmosphere, called wind.
The immediate cause of wind is the uneven distribution of air pressure along the surface of the earth. The main characteristics of the wind are: direction / part of the horizon from where the wind blows / and speed, measured in m/s, knots (1kt~0.5 m/s) and km/h (I m/s = 3.6 km/h).
The wind is characterized by gusty speed and variability of direction. To characterize the wind, the average speed and average direction are determined.
According to instruments, the wind is determined from the true meridian. At those airports where the magnetic declination is 5° or more, corrections for magnetic declination are introduced into the heading indication for transmission to ATS units, crews, in AT1S and VHF weather reports. In reports distributed outside the aerodrome, the direction of the wind is indicated from the true meridian.
Averaging takes place 10 minutes before the release of the report outside the aerodrome and 2 minutes at the aerodrome (on ATIS and at the request of the air traffic controller). Gusts are indicated in relation to average speed in case of a difference of 3 m/s, if the wind is lateral (each airport has its own gradations), and in other cases after 5 m/s.
Squall - a sharp, sudden increase in wind that occurs for 1 minute or more, while the average speed differs by 8 m / s or more from the previous average speed and with a change in direction.
The duration of a squall is usually several minutes, the speed often exceeds 20-30 m/s.
The force that causes a mass of air to move horizontally is called the baric gradient force. The greater the pressure drop, the stronger the wind. The movement of air is influenced by the Coriolis force, the force of friction. The Coriolis force deflects all air currents to the right in the Northern Hemisphere and does not affect wind speed. The friction force acts opposite to the movement and decreases with height (mainly in the surface layer) and above 1000-1500m has no effect. The friction force reduces the angle of deviation of the air flow from the direction of the horizontal baric gradient, i.e. affects the direction of the wind.
Gradient wind is the movement of air in the absence of friction. All wind above 1000m is practically gradient.
The gradient wind is directed along the isobars so that the low pressure will always be to the left of the flow. In practice, the wind at heights is predicted from baric topography maps.
The wind has a great influence on the flights of all types of aircraft. From the direction and speed of the wind in relation to the runway, the safety of the takeoff and landing of the aircraft depends. The wind affects the length of the takeoff and run of the aircraft. Dangerous and side wind, which causes the demolition of the aircraft. The wind causes dangerous phenomena that complicate flights, such as hurricanes, squalls, dust storms, snowstorms. The structure of the wind is turbulent, which causes turbulence and aircraft throws. When choosing an aerodrome runway, the prevailing wind direction is taken into account.
2.6 Local winds Local winds are an exception to the baric wind law: they blow along a horizontal baric gradient, which appears in a given area due to unequal heating of different parts of the underlying surface or due to relief.
These include:
Breezes that are observed on the coast of the seas and large bodies of water, blowing on land from the water surface during the day and vice versa at night, they are respectively called sea and coastal breezes, the speed is 2-5 m / s, they spread vertically up to 500-1000 m. The reason for their occurrence uneven heating of water and land. Breezes affect the weather conditions in the coastal strip, causing a decrease in temperature, an increase in absolute humidity, and wind shifts. Breezes are pronounced on the Black Sea coast of the Caucasus.
Mountain-valley winds arise as a result of uneven heating and cooling of air directly at the slopes. During the day, the air rises up the slope of the valley and is called the valley wind. At night it descends from the slopes and is called mountainous. The vertical thickness of 1500 m often causes turbulence.
Föhn is a warm, dry wind that blows from the mountains into the valleys, sometimes reaching storm strength. The foehn effect is expressed in the region high mountains 2-3km. It occurs when a pressure difference is created on opposite slopes. On one side of the ridge there is an area of low pressure, on the other an area of high pressure, which contributes to the transshipment of air through the ridge. On the windward side, the rising air is cooled to the level of condensation (conditionally the lower boundary of the clouds) according to the dry adiabatic law (1 ° / 100 m.), Then according to the humid adiabatic law (0.5 ° -0.6 ° / 100 m.), Which leads to the formation of clouds and precipitation. When the stream crosses the ridge, it begins to quickly fall down the slope and heat up (1 ° / 100 m.). As a result, clouds are washed away from the lee side of the ridge and the air reaches the foot of the mountains very dry and warm. During the foehn, difficult weather conditions are observed on the windward side of the ridge (fog, precipitation) and cloudy weather on the leeward side of the ridge, but there is intense storm turbulence here.
Bora is a strong gusty wind blowing from the coastal low mountains (no more than 1000
m) to the side warm sea. It is observed in the autumn-winter period, accompanied by a sharp drop in temperature, expressed in the Novorossiysk region, northeast. Bora occurs in the presence of an anticyclone formed and located over the eastern and southeastern regions of the European territory of Russia, and over the Black Sea at this time a low pressure area, while large baric gradients are created and cold air falls through the Markhotsky pass from a height of 435 m into the Novorossiysk bay at a speed of 40-60 m/sec. Bora causes a storm at sea, ice, spreads deep into the sea for 10-15 km, the duration is up to 3 days, and sometimes more.
A very strong bora is formed on Novaya Zemlya. On Lake Baikal, a bora-type wind forms at the mouth of the Sarma River and is locally called Sarma.
Afghan - A very strong, dusty west or southwest wind in the eastern Karakum, up the valleys of the Amu Darya, Syr Darya and Vakhsh rivers. Accompanied by dust storms and thunderstorms. Afghanets arises in connection with the frontal intrusions of cold within the Turan lowland.
Local winds, characteristic of certain areas, have a great influence on the work of aviation. Strengthening of the wind caused by the terrain features of the area makes it difficult to pilot the aircraft at low altitudes, and sometimes it is dangerous for the flight.
When the air stream crosses mountain ranges, lee waves are formed in the atmosphere. They occur when:
The presence of wind blowing perpendicular to the ridge, the speed of which is 50 km/h or more;
Gain in wind speed with height;
The presence of layers of inversion or isotherm from the top of the ridge for 1-3 km. The lee waves cause intense turbulence of aircraft. They are characterized by lenticular altocumulus clouds.
3.Vertical air movement
3.1 Causes and types of vertical air movements Vertical movements constantly occur in the atmosphere. They play an important role in such atmospheric processes as the vertical transfer of heat and water vapor, the formation of clouds and precipitation, the dissipation of clouds, the development of thunderstorms, the emergence of turbulent zones, etc.
Depending on the causes of occurrence, the following types of vertical movements are distinguished:
Thermal convection - occurs due to uneven heating of air from the underlying surface. Warmer volumes of air, becoming lighter than the environment, rise up, giving way to denser cold air descending. The speed of ascending movements can reach several meters per second, and in some cases 20-30 m/s (in powerful cumulus, cumulonimbus clouds).
Downdrafts are smaller (~ 15 m/s).
Dynamic convection or dynamic turbulence - disordered vortex movements that occur during horizontal movement and friction of air on the earth's surface. The vertical components of such movements can be several tens of cm/s, less often up to several m/s. This convection is well expressed in the layer from the ground to a height of 1-1.5 km (boundary layer).
Thermal and dynamic convection are often observed simultaneously, determining the unstable state of the atmosphere.
Ordered, forced vertical movements are the slow upward or downward movement of the entire air mass. This may be a forced rise of air in the zone of atmospheric fronts, in mountainous regions on the windward side, or a slow calm "settlement" of the air mass as a result of general circulation atmosphere.
The convergence of air flows in the upper layers of the troposphere (convergence) of air flows in the upper atmosphere causes an increase in pressure near the ground and downward vertical movements in this layer.
The divergence of air flows at heights (divergence), on the contrary, leads to a drop in pressure near the ground and an upward rise in air.
Wave motions - arise due to the difference in air density and speed of its movement at the upper and lower boundaries of the layers of inversion and isotherm. In the crests of the waves, ascending movements are formed, in the valleys - descending. Wave motions in the atmosphere can be observed in the mountains on the lee side, where lee (standing) waves form.
During flights in the air mass, where strongly developed vertical currents are observed, the aircraft experiences chatter and surges that complicate piloting. Large-scale vertical air currents can cause large vertical movements of the aircraft independent of the pilot. This can be especially dangerous when flying at altitudes close to the practical ceiling of the aircraft, where the updraft can lift the aircraft to a height much higher than the ceiling, or when flying in mountainous areas on the lee side of the ridge, where the downdraft can cause the aircraft to collide with the ground. .
Vertical air movements lead to the formation of cumulonimbus clouds dangerous for flights.
4.Clouds and precipitation
4.1 Reasons for the formation of clouds. Classification.
Clouds are visible accumulations of water droplets and ice crystals suspended in the air at a certain height above the earth's surface. Clouds form as a result of condensation (transition of water vapor into a liquid state) and sublimation (transition of water vapor directly into a solid state) of water vapor.
The main reason for the formation of clouds is the adiabatic (without heat exchange with the environment) decrease in temperature in the rising moist air, leading to the condensation of water vapor; turbulent exchange and radiation, as well as the presence of condensation nuclei.
Cloud microstructure - the phase state of cloud elements, their size, the number of cloud particles per unit volume. Clouds are divided into ice, water and mixed (from crystals and drops).
According to the international classification, clouds are divided into 10 main forms according to their appearance, and into four classes according to heights.
1. Clouds of the upper tier - located at an altitude of 6000 m and above, they are thin white clouds, consist of ice crystals, have little water content, so they do not give precipitation. The power is small: 200 m - 600 m. These include:
Cirrus clouds /Ci-cirrus/, having the appearance of white threads, hooks. They are harbingers of worsening weather, the approach of a warm front;
Cirrocumulus / Cc- cirrocumulus / - small lambs, small white flakes, ripples. The flight is accompanied by a weak turbulence;
Cirrostratus / Cs-cirrostratus / have the appearance of a bluish uniform veil that covers the entire sky, a blurry disk of the sun is visible, at night - a halo circle appears around the moon. Flight in them may be accompanied by light icing, electrization of the aircraft.
2. Clouds of the middle tier are located at a height from to
2km 6km, consist of supercooled drops of water mixed with snowflakes and ice crystals, flights in them are accompanied by poor visibility. These include:
Altocumulus / Ac-altocumulus / having the appearance of flakes, plates, waves, ridges, separated by gaps. Vertical length 200-700m. Precipitation does not fall, the flight is accompanied by bumpiness, icing;
Altostratus / As-altostratus / are a continuous gray shroud, thin altostratus have a thickness of 300-600 m, dense - 1-2 km. In winter, heavy precipitation falls from them.
The flight is accompanied by icing.
3. Low clouds are located from 50 to 2000 m, have a dense structure, they have poor visibility, and icing is often observed. These include:
Nimbostratus/Ns-nimbostratus/ having a dark gray color, high water content, give abundant precipitation. Under them, low fractonimbus/Frnb-fractonimbus/ clouds form in the precipitation. The height of the lower boundary of nimbostratus clouds depends on the proximity of the front line and ranges from 200 to 1000 m, the vertical length is 2-3 km, often merging with high-stratus and cirrostratus clouds;
Stratocumulus / Sc-stratocumulus / consist of large ridges, waves, plates separated by gaps. The lower limit is 200-600 m, and the thickness of the clouds is 200-800 m, sometimes 1-2 km. These are intramass clouds, in the upper part of the stratocumulus clouds the highest water content, here is the icing zone. Precipitation from these clouds, as a rule, does not fall;
Stratus clouds / St-stratus / are a continuous uniform cover hanging low above the ground with jagged blurry edges. The height is 100-150 m and below 100 m, and the upper limit is -300-800 m. Takeoff and landing are drastically complicated, and drizzling precipitation is produced. They can sink to the ground and turn into fog;
Fractured-layered / St Fr-stratus fractus / clouds have a lower boundary of 100 m and below 100 m, are formed as a result of radiation fog dispersion, precipitation does not fall out of them.
4. Clouds of vertical development. Their lower boundary lies in the lower tier, the upper one reaches the tropopause. These include:
Cumulus clouds / Cu cumulus / - dense cloud masses developed vertically with white domed tops and with a flat base. Their lower limit is about 400-600 m and higher, the upper limit is 2-3 km, they do not give precipitation. Flight in them is accompanied by turbulence, which does not significantly affect the flight mode;,..
Powerful cumulus / Cu cong-cumulus congestus / clouds are white dome-shaped peaks with a vertical development of up to 4-6 km, do not give precipitation. The flight in them is accompanied by moderate to strong turbulence, so it is forbidden to enter these clouds;
Cumulonimbus (thunderstorm) / Cb-cumulonimbus / are the most dangerous clouds, they are powerful masses of swirling clouds with a vertical development of up to 9-12 km and above. They are associated with thunderstorms, showers, hail, intense icing, intense turbulence, squalls, tornadoes, wind shifts. Cumulonimbus at the top look like an anvil, in the direction of which the cloud is shifting.
Depending on the causes of occurrence, the following types of cloud forms are distinguished:
1. Cumulus. The reason for their occurrence is thermal, dynamic convection and forced vertical movements.
These include:
a) cirrocumulus /Cc/
b) altocumulus /Ac/
c) stratocumulus /Sc/
d) powerful cumulus / Сu cong /
e) cumulonimbus /Cb/
2. Stratified ones arise as a result of ascending glides of warm moist air along an inclined surface of cold air, along gentle frontal sections. These types of clouds include:
a) pinnately stratified/Cs/
b) high-layered /As/
c) stratified rain / Ns /
3. Wavy, occur during wave oscillations on layers of inversion, isotherm and in layers with a small vertical temperature gradient.
These include:
a) altocumulus undulate
b) stratocumulus undulate.
4.2 Observations of clouds When observing clouds, the following are determined: the total number of clouds (indicated in oktants.) the number of clouds of the lower tier, the shape of the clouds.
The height of the lower tier clouds is determined instrumentally using the light locator IVO, DVO with an accuracy within ±10% in the altitude range from 10 m to 2000 m. In the absence of instrumental means, the height is estimated from the data of the aircraft crews or visually.
In case of fog, precipitation or dust storm, when it is impossible to determine the base of the clouds, the results of instrumental measurements are indicated in the reports as vertical visibility.
At aerodromes equipped with landing approach systems, the height of the cloud base at its values of 200 m and below is measured with the help of sensors installed in the BPRM area. In other cases, the measurement is made at the working starts. When estimating the expected low cloud height, the terrain is taken into account.
Above elevated places, the clouds are located lower by 50-60% of the difference in the excess of the points themselves. Over forest areas, cloudiness is always lower. Over industrial centers, where there are many condensation nuclei, the frequency of cloudiness increases. The lower edge of low clouds of stratus, fractured-stratus, fractured rain is uneven, changeable and experiences significant fluctuations within 50-150 m.
Clouds are one of the most important meteorological elements affecting flights.
4.3 Precipitation Water droplets or ice crystals that fall from clouds onto the Earth's surface are called precipitation. Precipitation usually falls from those clouds that are mixed in structure. For precipitation, it is necessary to enlarge drops or crystals up to 2-3 mm. The drops are enlarged due to their coalescence upon collision.
The second enlargement process is associated with the transfer of water vapor from water droplets to the crystal, and it grows, which is associated with different saturation elasticity above water and above ice. Precipitation occurs from clouds that reach those levels where active crystal formation occurs, i.e. where temperatures are in the range of -10°C-16°C and below. According to the nature of precipitation, precipitation is divided into 3 types:
Heavy precipitation - falls for a long time and for large area from nimbostratus and altostratus clouds;
Showers from cumulonimbus clouds, in a limited area, in a short period of time and in large quantities; drops are larger, snowflakes - flakes.
Drizzling - from stratus clouds, these are small droplets, the fall of which is not noticeable to the eye.
By type, they distinguish: rain, snow, freezing rain passing through the surface layer of air with a negative temperature, drizzle, groats, hail, snow grains, etc.
Precipitation includes: dew, hoarfrost, frost and blizzards.
In aviation, precipitation that leads to the formation of ice is called supercooled. These are supercooled drizzle, supercooled rain and supercooled fog (observed or predicted in temperature gradations from -0° to -20°C). Precipitation complicates the flight of an aircraft - worsens horizontal visibility. Precipitation is considered heavy when the visibility is less than 1000 m, regardless of the nature of the precipitation (following, torrential, drizzling). In addition, the water film on the cab windows causes optical distortion visible objects, which is dangerous for takeoff and landing. Precipitation affects the condition of airfields, especially unpaved ones, and supercooled rain causes ice and icing. Hitting the hail zone causes serious technical damage. When landing on a wet runway, the length of the aircraft run changes, which can lead to overrunning the runway. A jet of water thrown off the landing gear can be sucked into the engine, causing a loss of thrust, which is dangerous during takeoff.
5. Visibility
There are several definitions of visibility:
The meteorological visibility range / MDL / is the greatest distance from which, during daylight hours, a black object of a sufficiently large size can be distinguished against the sky near the horizon. At night, the distance to the most distant visible point source of light of a certain strength.
The meteorological visibility range is one of the important meteorological elements for aviation.
To monitor visibility at each aerodrome, a map of landmarks is drawn up and visibility is determined using instrumental systems. Upon reaching SMU (200/2000) - visibility measurement should be carried out using instrumental systems with recording readings.
The averaging period is -10 min. for reports outside the aerodrome; 1 min. - for local regular and special reports.
Runway visual range /RVR/ - the visual range within which the pilot of an aircraft located on the runway center line can see the runway pavement markings or lights that indicate the contours of the runway and its center line.
visibility observations are made along the runway with the help of instruments or on boards on which single light sources (60 W light bulbs) are installed to assess visibility in the dark.
Since visibility can be very variable, visibility instruments are installed at the VTS on both courses and at the middle of the runway. The weather report includes:
a) runway length or less, the smaller of the two 2000m visibility measured at both ends of the runway;
b) when the runway length is more than 2000 m - the lesser of the two values of visibility measured at the working start and the middle of the runway.
At aerodromes where JVI lighting systems are used with a visibility of 1500 m or less at dusk and at night, 1000 m or less during the day, recalculation is made according to the tables into the JVI visibility, which is also included in air weather. Recalculation of visibility into visibility of HMI only at night.
In difficult weather conditions, especially at the time of landing of the aircraft, it is important to know the oblique visibility. Oblique visibility (landing) is the maximum slope distance along the descent glide path at which the pilot of a landing aircraft, when switching from instrument piloting to visual piloting, can detect the beginning of the runway. It is not measured, but evaluated. The following dependence of oblique visibility on the value of horizontal visibility at different cloud heights has been experimentally established:
When the height of the base of the clouds is less than 100 m and the deterioration of visibility due to haze, precipitation near the ground, oblique visibility is 25-45% of the horizontal visibility;
At a height of the lower cloud boundary of 100-150 m, it is equal to 40-50% of the horizontal; - at a height of 150-200 m, the slope is 60-70% of the horizontal;
– – –
When the height of the NGO is more than 200 m, the oblique visibility is close to or equal to the horizontal visibility near the ground.
Fig.2 Effect of haze in the atmosphere on oblique visibility.
inversion
6. The main atmospheric processes that determine the weather Atmospheric processes observed over large geographic areas and studied using synoptic maps are called synoptic processes.
These processes are the result of the emergence, development and interaction of air masses, divisions between them - atmospheric fronts and cyclones and anticyclones associated with the indicated meteorological objects.
During pre-flight preparation, the aircraft crew must study the meteorological situation and flight conditions on the AMSG along the route, at the airports of departure and landing, at alternate aerodromes, paying attention to the main atmospheric processes that cause the weather:
On the state of the air masses;
On the location of baric formations;
On the position of atmospheric fronts relative to the flight route.
6.1 Air masses Large masses of air in the troposphere with uniform weather conditions and physical properties are called air masses (AM).
There are 2 classifications of air masses: geographical and thermodynamic.
Geographic - depending on the areas of their formation, they are divided into:
a) arctic air (AB)
b) temperate/polar/air (HC)
d) tropical air (TV)
e) equatorial air (EI) Depending on the underlying surface, over which this or that air mass has been located for a long time, they are divided into marine and continental.
Depending on the thermal state (in relation to the underlying surface), air masses can be warm and cold.
Depending on the conditions of vertical balance, there are stable, unstable and indifferent stratification (state) of air masses.
A stable VM is warmer than the underlying surface. There are no conditions for the development of vertical air movements in it, since cooling from below reduces the vertical temperature gradient due to a decrease in the temperature contrast between the lower and upper layers. Here, layers of inversion and isotherm are formed. Most favorable time for the acquisition of the stability of the VM over the continent is during the day night, during the year - winter.
The nature of the weather in the UWM in winter: low sub-inversion stratus and stratocumulus clouds, drizzle, haze, fog, ice, icing in the clouds (Fig. 3).
Difficult conditions only for takeoff, landing and visual flights, from the ground up to 1-2 km, cloudy above. In summer, cloudy weather or cumulus clouds with weak turbulence up to 500 m prevails in the UVM, visibility is somewhat worse due to dustiness.
HCW circulates in the warm sector of the cyclone and on the western periphery of anticyclones.
Rice. 3. Weather in UVM in winter.
An unstable air mass (NVM) is a cold VM in which favorable conditions are observed for the development of ascending air movements, mainly thermal convection. When moving over a warm underlying surface, the lower layers of the cold air warm up, which leads to an increase in vertical temperature gradients up to 0.8 - 1.5/100 m, as a result of this, to the intensive development of convective movements in the atmosphere. The NVM is most active in the warm season. With sufficient moisture content of the air, cumulonimbus clouds develop up to 8-12 km, showers, hail, intramass thunderstorms, and squally wind intensifications. The daily course of all elements is well expressed. With sufficient humidity and subsequent nighttime clearing, radiation fogs can occur in the morning.
Flying in this mass is accompanied by bumpiness (Fig. 4).
In the cold season in NVM, there are no difficulties in flights. As a rule, it is clear, snow blowing, blowing snow, with north and northeast winds, and with a northwest intrusion of cold air, clouds are observed with a lower boundary of at least 200-300 m of the stratocumulus or cumulonimbus type with snow charges.
Secondary cold fronts can occur in the NVM. NVM circulates in the rear part of the cyclone and on the eastern periphery of anticyclones.
6.2 Atmospheric fronts The transition zone /50-70 km./ between two air masses, characterized by a sharp change in the values of meteorological elements in the horizontal direction, is called an atmospheric front. Each front is a layer of inversion /or isotherm/, but these inversions are always inclined at a slight angle to the ground towards the cold air.
The wind in front of the front at the surface of the earth turns to the front and intensifies, at the moment the front passes, the wind turns to the right / clockwise /.
Fronts are zones of active interaction between warm and cold VMs. Along the surface of the front, an ordered rise of air occurs, accompanied by condensation of the water vapor contained in it. This leads to the formation of powerful cloud systems and precipitation at the front, causing the most difficult weather conditions for aviation.
Frontal inversions are dangerous with chatter, because. in this transition zone, two air masses move with different air densities, with different speeds and wind directions, which leads to the formation of eddies.
To assess the actual and expected weather conditions on the route or in the area of flights great importance has an analysis of the position of atmospheric fronts relative to the flight route and their movement.
Before departure, it is necessary to assess the activity of the front according to the following criteria:
The fronts are located along the axis of the trough; the more pronounced the trough, the more active the front;
When passing through the front, the wind undergoes sharp changes in direction, convergence of streamlines is observed, as well as their changes in speed;
The temperature on both sides of the front undergoes sharp changes, temperature contrasts are 6-10° or more;
The baric tendency is not the same on both sides of the front, it decreases in front of the front, increases behind the front, sometimes the pressure change in 3 hours is 3-4 hPa or more;
Along the front line there are clouds and precipitation zones characteristic of each type of front. The wetter the VM in the front zone, the more active the weather. On high-altitude maps, the front is expressed in the condensation of isohypses and isotherms, in sharp contrasts in temperature and wind.
The front moves in the direction and with the speed of the gradient wind observed in cold air or its component directed perpendicular to the front. If the wind is directed along the front line, then it remains inactive.
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Atmosphere
Composition and properties of air.
The atmosphere is a mixture of gases, water vapor and aerosols (dust, condensation products). The share of the main gases is: nitrogen 78%, oxygen 21%, argon 0.93%, carbon dioxide 0.03%, the share of others is less than 0.01%.
Air is characterized by the following parameters: pressure, temperature and humidity.
International standard atmosphere.
temperature gradient.
Air is heated by the ground, and density decreases with height. The combination of these two factors creates a normal situation of warmer air near the surface and gradually cooling with altitude.
Humidity.
Relative humidity is measured as a percentage as the ratio of the actual amount of water vapor in the air to the maximum possible at a given temperature. Warm air can dissolve more water vapor than cold air. As the air cools, its relative humidity approaches 100% and clouds begin to form.
Cold air in winter is closer to saturation. Therefore, in winter, a lower cloud base and their distribution.
Water can be in three forms: solid, liquid, gaseous. Water has a high heat capacity. In the solid state, it has a lower density than in the liquid state. As a result, it moderates the global climate. The gaseous state is lighter than air. The weight of water vapor is 5/8 of the weight of dry air. As a result, moist air rises above dry air.
Atmospheric movement
Wind.
Wind arises from a pressure imbalance, usually in a horizontal plane. This imbalance appears due to differences in air temperatures in adjacent areas or vertical air circulation in different areas. The root cause is solar heating of the surface.
The wind is named after the direction from which it blows. For example: the north blows from the north, the mountain - from the mountains, the valley - to the mountains.
Coriolis effect.
The Coriolis effect is very important for understanding global processes in the atmosphere. The result of this effect is that all objects moving in the northern hemisphere tend to turn to the right, and in the southern - to the left. The Coriolis effect is strongly pronounced at the poles and vanishes at the equator. The reason for the Coriolis effect is the rotation of the Earth under moving objects. This is not some real force, this is an illusion of right rotation for all freely moving bodies. Rice. 32
Air masses.
An air mass is called air having the same temperature and humidity, over a territory of at least 1600 km. The air mass can be cold if it was formed in the polar regions, warm - from tropical zone. It can be marine or continental in terms of humidity.
When CWM arrives, the surface layer of air is heated from the ground, which increases instability. When TBM arrives, the ground layer of air cools, descends and forms an inversion, increasing stability.
Cold and warm front.
A front is the boundary between warm and cold air masses. If cold air is moving forward, it is a cold front. If warm air moves forward - a warm front. Sometimes air masses move until they are stopped by the increased pressure in front of them. In this case, the frontal boundary is called a stationary front.
Rice. 33 cold front warm front
front of occlusion.
Clouds
Cloud types.
There are only three main types of clouds. These are stratus, cumulus and cirrus i.e. stratiform (St), cumulus (Cu) and pinnate (Ci).
stratus cumulus cirrus Fig. 35
Classification of clouds by height:
Rice. 36
Lesser known clouds:
Haze - Formed when warm and humid air moves ashore, or when the earth radiates heat at night into a cold and humid layer.
Cloud cap - formed above the top when dynamic updrafts occur. Fig.37
Clouds in the form of a flag - are formed behind the tops of the mountains in strong winds. Sometimes it consists of snow. Fig.38
Rotor clouds - can form on the lee side of the mountain, behind the ridge in strong winds and have the form of long wisps located along the mountain. They form on the ascending sides of the rotor and collapse on the descending ones. Indicate severe turbulence. Fig. 39
Wave or lenticular clouds - are formed during the wave movement of air in strong winds. They do not move relative to the ground. Fig.40
Rice. 37 Fig. 38 Fig.39
Ribbed clouds - very similar to ripples on the water. Formed when one layer of air moves over another at a speed sufficient to form waves. They move with the wind. Fig.41
Pileus - when a thundercloud develops to an inversion layer. A thundercloud can break through inversion layer. Rice. 42
Rice. 40 Fig. 41 Fig. 42
Cloud formation.
Clouds are made up of countless microscopic water particles of various sizes, from 0.001 cm in saturated air to 0.025 cm with continued condensation. Main way formation of clouds in the atmosphere - the cooling of moist air. This happens when the air cools as it rises.
Fog forms in cooling air from contact with the ground.
Upstreams.
There are three main causes of updrafts. These are flows due to the movement of fronts, dynamic and thermal.
front dynamic thermal
The rate of rise of the frontal flow directly depends on the speed of the front and is usually 0.2-2 m/s. In a dynamic flow, the lifting speed depends on the strength of the wind and the steepness of the slope, it can reach up to 30 m/s. Thermal flow occurs when warmer air rises and sunny days heated by the earth's surface. The lifting speed reaches 15 m/s, but usually it is 1-5 m/s.
Dew point and cloud height.
The saturation temperature is called the dew point. Assume that rising air is cooled in a certain way, for example, 1 0 С/100 m. But the dew point drops only by 0.2 0 С/100 m. Thus, the dew point and the temperature of the rising air converge by 0.8 0 С/100 m. When they equalize, clouds will form. Meteorologists use dry and wet bulbs to measure ground and saturation temperatures. From these measurements, you can calculate the base of the clouds. For example: the air temperature at the surface is 31 0 C, the dew point is 15 0 C. Dividing the difference by 0.8, we get a base equal to 2000m.
Cloud life.
Clouds during their development go through the stages of origin, growth and decay. One isolated cumulus cloud lives for about half an hour from the moment the first signs of condensation appear to decay into an amorphous mass. However, often the clouds do not break up as quickly. This occurs when the air humidity is at cloud level and cloud level is the same. The mixing process is in progress. In fact, ongoing thermality results in a gradual or rapid spread of cloud cover over the entire sky. This is called overdevelopment, or OD in the lexicon of airmen.
Continuing thermals can also feed individual clouds, increasing their lifetime by more than 0.5 hours. In fact, thunderstorms are long-lived clouds formed by thermal flows.
Precipitation.
Precipitation requires two conditions: continuous updrafts and high humidity. In the cloud, water droplets or ice crystals begin to grow. When they get big, they start to fall. It is snowing, raining or hail.
MINISTRY OF HIGHER AND SECONDARY SPECIAL EDUCATION OF THE REPUBLIC OF UZBEKISTAN
TASHKENT STATE AVIATION INSTITUTE
Department: "Air Traffic Control"
Lecture summary
on the course "Aviation meteorology"
TASHKENT - 2005
"Aviation meteorology"
Tashkent, TGAI, 2005.
The lecture summary includes basic information about meteorology, atmosphere, winds, clouds, precipitation, synoptic weather maps, baric topography maps and radar conditions. The movement and transformation of air masses, as well as baric systems, are described. The issues of movement and evolution of atmospheric fronts, fronts of occlusion, anticyclones, snowstorms, types and forms of icing, thunderstorms, lightning, atmospheric turbulence and regular traffic - METAR, the international aviation code TAF are considered.
The lecture notes were discussed and approved at a meeting of the Department of Internal Affairs
Approved at a meeting of the Method Council of the FGA
Lecture #1
1. The subject and significance of meteorology.:
2. Atmosphere, composition of the atmosphere.
3. The structure of the atmosphere.
meteorology called the science of the actual state of the atmosphere and the phenomena occurring in it.
under the weather It is customary to understand the physical state of the atmosphere at any moment or period of time. The weather is characterized by a combination of meteorological elements and phenomena, such as atmospheric pressure, wind, humidity, air temperature, visibility, precipitation, clouds, icing, ice, fog, thunderstorms, snowstorms, dust storms, tornadoes, various optical phenomena (halos, crowns) .
Climate - long-term weather regime: typical for this place, developing under the influence of solar radiation, the nature of the underlying surface, atmospheric circulation, changes in the earth and atmosphere.
Aviation meteorology studies meteorological elements and atmospheric processes from the point of view of their influence on aviation technology and aviation activities, and also develops methods and forms of meteorological support for flights. The correct consideration of meteorological conditions in each particular case for the best safety, economy and efficiency of flights depends on the pilot and controller, on their ability to use meteorological information.
The flight and dispatching staff must know:
What exactly is the effect of individual meteorological elements and weather phenomena on the operation of aviation;
Have a good understanding of the physical nature of atmospheric processes that create various weather conditions and their changes in time and space;
Know the methods of operational meteorological support for flights.
The organization of civil aviation flights of civil aviation on a global scale, and the meteorological support of these flights, is unthinkable without international cooperation. There are international organizations that regulate the organization of flights and their meteorological support. These are ICAO (International Civil Aviation Organization) and WMO (World Meteorological Organization), which closely cooperate with each other on all matters of collection and dissemination of meteorological information in the interests of civil aviation. Cooperation between these organizations is governed by special working agreements concluded between them. ICAO defines the requirements for meteorological information arising from GA requests, while WMO determines the scientifically based possibilities to meet them and develops recommendations and regulations, as well as various guidance materials that are mandatory for all its member countries.
Atmosphere.
The atmosphere is the air envelope of the earth, consisting of a mixture of gases and colloidal impurities. ( dust, drops, crystals).
The earth is, as it were, the bottom of a vast ocean of air, and all living and growing on it owe their existence to the atmosphere. It delivers the oxygen we need to breathe, protects us from deadly cosmic rays and solar ultraviolet radiation, and protects the earth's surface from extreme heat during the day and extreme cooling at night.
In the absence of an atmosphere, the temperature of the surface of the globe during the day would reach 110° and more, and at night it would drop sharply to 100° below zero. Complete silence would reign everywhere, since sound cannot propagate in the void, day and night would change instantly, and the sky would be absolutely black.
The atmosphere is transparent, but it constantly reminds us of itself: rain and snow, thunderstorm and blizzard, hurricane and calm, heat and frost - all this is a manifestation of atmospheric processes that take place under the influence of solar energy and when the atmosphere interacts with the earth's surface itself.
The composition of the atmosphere.
Up to a height of 94-100 km. the composition of the air in percentage terms remains constant - the homosphere (“homo” from Greek is the same); nitrogen - 78.09%, oxygen - 20.95%, argon - 0.93%. In addition, the atmosphere contains a variable amount of other gases (carbon dioxide, water vapor, ozone), solid and liquid aerosol impurities (dust, gases industrial enterprises, smoke, etc.).
The structure of the atmosphere.
Data from direct and indirect observations show that the atmosphere has a layered structure. Depending on what physical property atmosphere (temperature distribution, air composition by altitude, electrical characteristics) is the basis for the division into layers, there are a number of schemes for the structure of the atmosphere.
The most common scheme of the structure of the atmosphere is the scheme, which is based on the distribution of temperature along the vertical. According to this scheme, the atmosphere is divided into five main spheres or layers: the troposphere, stratosphere, mesosphere, thermosphere and exosphere.
interplanetary outer space | |||
The upper boundary of the geocorona | |||
Exosphere (Sphere of Scattering) |
|||
Thermopause | |||
Thermosphere (ionosphere) | |||
mesopause | |||
Mesosphere | |||
Stratopause | |||
Stratosphere | |||
tropopause | |||
Troposphere | |||
The table shows the main layers of the atmosphere and their average heights in temperate latitudes. Control questions. 1. What aviation meteorology studies. 2. What functions are assigned to IKAO, WMO? |
|||
3. What functions are assigned to the Glavgidromet of the Republic of Ukhzbekistan?
4. Describe the composition of the atmosphere.
Lecture number 2.
1. The structure of the atmosphere (continued).
2. Standard atmosphere.
Troposphere - the lower part of the atmosphere, on average, up to a height of 11 km, where 4/5 of the entire mass of atmospheric air and almost all of the water vapor are concentrated. Its height varies depending on the latitude of the place, time of year and day. It is characterized by an increase in temperature with height, an increase in wind speed, the formation of clouds and precipitation. There are 3 layers in the troposphere:
1. Border (friction layer) - from the ground up to 1000 - 1500 km. This layer is affected by the thermal and mechanical effects of the earth's surface. The daily variation of meteorological elements is observed. The lower part of the boundary layer with a thickness of 600m is called the "surface layer". The atmosphere above 1000 - 1500 meters is called the "free atmosphere layer" (without friction).
2. The middle layer extends from the upper boundary of the boundary layer to a height of 6 km. Here, the influence of the earth's surface almost does not affect. Weather conditions depend on atmospheric fronts and vertical balance of air masses.
3. The upper layer lies above 6 km. and extends to the tropopause.
tropopause - transitional layer between the troposphere and the stratosphere. The thickness of this layer is from several hundred meters to 1 - 2 km, and the average temperature is from minus 70 ° - 80 ° in the tropics.
The temperature in the tropopause layer can remain constant or increase (inversion). In this regard, the tropopause is a powerful retaining layer for vertical air movements. When crossing the tropopause at the echelon, temperature changes, changes in moisture content and air transparency can be observed. In the zone of the tropopause or its lower boundary, the minimum wind speed is usually located.
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