“PRACTICAL AVIATION METEOROLOGY A training manual for flight and traffic control personnel of civil aviation. Compiled by V.A. Pozdnyakova, teacher of the Ural Training Center for Civil Aviation. Ekaterinburg 2010...”
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Ural Training Center of Civil Aviation
PRACTICAL AVIATION
METEOROLOGY
Training manual for flight and air traffic control personnel
Compiled by a teacher of the Ural Training Center of Civil Aviation
Pozdnyakova V.A.
Ekaterinburg 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 Causes of cloud formation. Cloud classification 12-13
4.2 Cloud observations 13
4.3 Precipitation 14 5 Visibility 14-15 6 Atmospheric processes that cause weather 16
6.1 Air masses 16-17
6.2 Atmospheric fronts 18
6.3 Warm front 18-19
6.4 Cold front 19-20
6.5 Occlusion fronts 20-21
6.6 Secondary fronts 22
6.7 Upper warm front 22
6.8 Stationary fronts 22 7 Pressure systems
7.1 Cyclone 23
7.2 Anticyclone 24
7.3 Movement and evolution of pressure systems 25-26
8. High-altitude frontal zones 26
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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 airplanes 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 knows the meteorological situation in the flight area, landing point and at alternate airfields. Therefore, it is necessary that every pilot has a perfect command of the necessary meteorological knowledge, understands the physical essence of weather phenomena, their connection with the development of synoptic processes and local physical and geographical conditions, which is the key to flight safety.
The proposed textbook sets out in a concise and accessible form the concepts of basic meteorological quantities and phenomena in connection with their influence on the operation of aviation. The meteorological conditions of the flight are considered and practical recommendations are given on the most appropriate actions of the flight crew in difficult meteorological conditions.
1. 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: the troposphere, stratosphere, mesosphere, thermosphere and exosphere.
Troposphere - extends from the earth's surface to an altitude of 10-12 km in temperate latitudes. It is lower at the poles and higher at the equator. The troposphere contains about 79% of the total mass of the atmosphere and almost all water vapor. Here there is a decrease in temperature with height, vertical air movements take place, and westerly winds, clouds and precipitation occur.
There are three layers in the troposphere:
a) Boundary (friction layer) - from the ground to 1000-1500 m. This layer is affected by the thermal and mechanical effects of the earth’s surface. The daily cycle of meteorological elements is observed. The lower part of the boundary layer, up to 600 m thick, is called the “ground layer”. Here the influence of the earth's surface is most strongly felt, as a result of which meteorological elements such as temperature, air humidity, and wind experience sharp changes with altitude.
The nature of the underlying surface largely determines the weather conditions of the surface layer.
b) The middle layer is located from the upper boundary of the boundary layer and extends to a height of 6 km. In this layer there is almost no influence of the earth's surface. Here weather conditions are determined mainly by atmospheric fronts and vertical convective air currents.
c) The top layer lies above the middle layer and extends to the tropopause.
Tropopause is a transition layer between the troposphere and stratosphere with a thickness of several hundred meters to 1-2 km. The lower limit of the tropopause is taken to be the altitude where the drop in temperature with height is replaced by an even temperature change, an increase or slowdown in the drop with height.
When crossing the tropopause at the flight level, changes in temperature, moisture content and air transparency may be observed. The maximum wind speed is usually located in the tropopause zone or below its lower boundary.
The height of the tropopause depends on the temperature of the tropospheric air, i.e. on the latitude of the place, 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 increases and at the upper boundary of the stratosphere approaches 0 degrees. It contains about 20% of the total mass of the atmosphere. Due to the insignificant content of water vapor in the stratosphere, clouds do not form, with the rare exception of the occasional nacreous clouds consisting of tiny supercooled droplets of water. Winds predominate from the west; in summer, above 20 km, there is a transition to easterly 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 gap - the stratopause, separating 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 altitude and reaches values of about -90°.
The transition layer between the mesosphere and thermosphere is the mesopause.
The thermosphere occupies altitudes from 80 to 450 km. According to indirect data and the results of rocket observations, the temperature here increases sharply with altitude and at the upper boundary of the thermosphere can be 700°-800°.
The exosphere is the outer layer of the atmosphere over 450 km.
1.1 Methods for studying the atmosphere 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 Earth satellites equipped with special equipment are used.
In addition to direct methods, valuable information about the state of the high layers of the atmosphere is provided by indirect methods based on the study of geophysical phenomena occurring in high layers of the atmosphere.
Laboratory experiments and mathematical modeling are carried out (a system of formulas and equations that allow obtaining numerical and graphical information about the state of the atmosphere).
1.2.Standard atmosphere The movement of an aircraft in the atmosphere is accompanied by complex interaction with it environment. The physical state of the atmosphere determines the aerodynamic forces that arise during flight, the thrust force created by the engine, fuel consumption, speed and maximum permissible flight altitude, readings of aeronautical instruments (barometric altimeter, speed indicator, Mach number indicator), etc.
The real atmosphere is very variable, so the concept of a standard atmosphere has been introduced for the design, testing and operation of aircraft. 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. Basic parameters of the standard atmosphere:
The atmosphere at all altitudes consists of dry air;
Taken as zero altitude (“ground”) average level sea, where the air pressure is 760 mm Hg. Art. or 1013.25 hPa.
Temperature +15°С
Air density is 1.225 kg/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 11 km, 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 a gas corresponds to a certain speed of molecular movement. The higher the average speed of molecular movement, the higher the air temperature. Temperature characterizes the degree of air heating.
For quantitative characteristics of temperature, the following scales are adopted:
The centigrade scale is the Celsius scale. On this scale, 0°C corresponds to the melting point of ice, 100°C corresponds to the boiling point of water, at a pressure of 760 mmHg.
Fahrenheit. The temperature of the mixture of ice and ammonia (-17.8° C) is taken as the lower temperature of this scale; the temperature of the human body is taken as the upper temperature. The interval is divided into 96 parts. Т°(С)=5/9 (Т°(Ф) -32).
In theoretical meteorology, an absolute scale is used - the Kelvin scale.
The zero of this scale corresponds to the complete cessation of thermal motion of molecules, i.e. lowest possible temperature. Т°(К)= Т°(С)+273°.
Heat is transferred from the earth's surface to the atmosphere through the following main processes: thermal convection, turbulence, radiation.
1) Thermal convection is the vertical rise of air heated over individual areas of the earth's surface. The strongest development of thermal convection is observed in the daytime (afternoon) hours. Thermal convection can spread 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 vortices (from the Latin turbo-vortex, whirlpool) that arise in a moving air flow due to its friction with the earth's surface and internal friction of particles.
Turbulence promotes air mixing and, consequently, heat exchange between the lower (hot) 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 by the earth’s surface of the heat it received 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 cools due to heat loss. 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 main role play: thermal convection and turbulence.
Temperature can change both horizontally along the earth's surface and vertically as it rises upward. The magnitude of the horizontal temperature gradient is expressed in degrees over a certain distance (111 km or 1° meridian). The greater the horizontal temperature gradient, the more dangerous phenomena (conditions) are formed in the transition zone, i.e. The activity of the atmospheric front increases.
The value characterizing 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 weather patterns. According to ISA y = 0.65° /100 m.
The layers of the atmosphere in which the temperature increases with height (у0°С) are called inversion layers.
Air layers in which the temperature does not change with height are called isothermal layers (y = 0 ° C). They are retaining 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 are formed. Inversions and isotherms can lead to significant vertical stratification of flows and the formation of significant vertical meter shifts, which causes aircraft to sway and affects flight dynamics during approach or takeoff.
Air temperature affects the flight of an airplane. The takeoff and landing performance of an aircraft largely depends on temperature. The length of the run and take-off distance, the length of the run and the landing distance decrease with decreasing temperature. Air density, which determines the flight characteristics of an aircraft, depends on temperature. As the temperature increases, the density decreases, and, consequently, the velocity pressure decreases and vice versa.
A change in speed pressure causes a change in engine thrust, lift, drag, horizontal and vertical speed. Air temperature affects flight altitude. Thus, increasing it at high altitudes by 10° from the standard leads to a lowering of the aircraft ceiling by 400-500 m.
Temperature is taken into account when calculating a safe flight altitude. Very low temperatures complicate the operation of aircraft. At air temperatures close to 0°C and below, with supercooled precipitation, ice forms, and when flying in the 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.
Air density determines the flight characteristics of an aircraft. The velocity head depends on the air density. The larger it is, the greater the velocity pressure and, therefore, the greater the aerodynamic force. The density of air, in turn, depends on temperature and pressure. From the Clapeyron-Mendeleev ideal gas equation of state P Density b-xa = ------, 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 therefore the velocity pressure decreases. When the temperature decreases, the opposite picture is observed.
A change in speed pressure causes a change in engine thrust, lift, drag and, consequently, the horizontal and vertical speeds of the aircraft.
The length of the run and landing distance is inversely proportional to air density and, therefore, temperature. A decrease in temperature by 15°C reduces the run length and take-off 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 water vapor content 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 more absolute humidity. It is used to judge the occurrence of vertical clouds and thunderstorm activity.
Relative humidity is characterized by the degree of saturation of air with water vapor. Relative humidity is the percentage of the actual amount of water vapor contained in the air to the amount required for complete saturation 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. As relative humidity increases, cloudiness decreases and visibility deteriorates.
Dew point temperature is the temperature at which water vapor contained in the air reaches a state of 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 the air must be cooled in order for the steam contained in it to reach a state of saturation. At dew point deficits of 3-4° or less, the air mass near the ground is considered humid, and at 0-1°, fogs often occur.
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 emitted by the earth's surface and atmosphere, and thereby reduces heat loss from our planet. The main influence of humidity on aviation operations 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 of 1 cm2 and equal to the weight of the air column extending through the entire atmosphere. Changes in pressure in space are closely related to the development of basic atmospheric processes. In particular, horizontal pressure inhomogeneity is the cause of air flows. The value of atmospheric pressure is measured in mmHg.
millibars and hectopascals. There is a dependency between them:
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1 mmHg = 1.33 mb = 1.33 hPa 760 mm Hg. = 1013.25 hPa.
The change in pressure in the horizontal plane per unit distance (1° of meridian arc (111 km) or 100 km is taken as a unit of distance) is called the horizontal pressure gradient. It is always directed towards low pressure. The wind speed depends on the magnitude of the horizontal pressure gradient, and the wind direction depends on its direction. In the northern hemisphere, the wind blows at an angle to the horizontal pressure gradient, so that if you stand with your back to the wind, 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 highlight pressure 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 ground-level synoptic weather maps, on which lines of equal baric trends - isallobars - are drawn.
Atmospheric pressure decreases with altitude. When conducting and managing flights, it is necessary to know the change in altitude depending on the vertical change in pressure.
This value is characterized by the pressure level - which determines the height to which one must rise or fall in order for the pressure to change by 1 mm Hg. or per 1 hPa. It is equal to 11 m per 1 mmHg, or 8 m per 1 hPa. At an altitude of 10 km, the step is 31 m with a pressure change of 1 mm Hg.
To ensure flight safety, crews are provided with air pressure in the weather, normalized to the threshold level of the working start runway in mmHg, mb, or pressure normalized to sea level for a standard atmosphere, depending on the type of aircraft.
The barometric altimeter on an airplane 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. Since the flight occurs at constant pressure, the flight is actually carried out on an isobaric surface. The uneven height of the isobaric surfaces leads to the fact that the true flight altitude can differ significantly from the instrument altitude.
So, above a cyclone it will be lower than the instrument one and vice versa. This should be taken into account when determining a safe flight level and when flying at altitudes close to the ceiling of the aircraft.
2.5 Wind In the atmosphere, horizontal movements of air, called wind, are always observed.
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/sec, knots (1 knot ~ 0.5 m/s) and km/hour (I m/sec = 3.6 km/hour).
Wind is characterized by gusty speed and variability of direction. To characterize the wind, the average speed and average direction are determined.
Using 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, and in AT1S and VHF weather reports. In reports disseminated beyond the aerodrome, the wind direction is indicated from the true meridian.
Averaging occurs 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 sideways (each airport has its own gradations), and in other cases after 5 m/s.
A squall is a sharp, sudden increase in wind that occurs over 1 minute or more, with the average speed differing by 8 m/s or more from the previous average speed and with a change in direction.
The duration of the 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 pressure 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 ground layer) and has no effect above 1000-1500m. The friction force reduces the angle of deviation of the air flow from the direction of the horizontal pressure gradient, i.e. also 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 low pressure will always be to the left of the flow. In practice, the wind at altitudes is predicted from pressure topography maps.
Wind has a great influence on the flights of all types of aircraft. The safety of aircraft takeoff and landing depends on the direction and speed of the wind relative to the runway. Wind affects the length of the aircraft's takeoff and run. Side winds are also dangerous, causing the plane to drift away. Wind causes dangerous phenomena that complicate flights, such as hurricanes, squalls, dust storms, and blizzards. The wind structure is turbulent, which causes the aircraft to bounce and throw. When choosing an aerodrome runway, the prevailing wind direction is taken into account.
2.6 Local winds Local winds are an exception to the pressure law of wind: they blow along a horizontal pressure gradient, which appears in a given area due to unequal heating of different parts of the underlying surface or due to the relief.
These include:
Breezes that are observed on the coast of seas and large bodies of water, blowing onto land from the water surface during the day and vice versa at night, they are respectively called sea and coastal breezes, speed 2-5 m/sec, vertically spreading up to 500-1000 m. The reason for their occurrence uneven heating of water and land. Breezes influence 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 mountain. A vertical thickness of 1500 m often causes bumpiness.
Foehn is a warm, dry wind blowing from the mountains to the valleys, sometimes reaching gale force. The foehn effect is expressed in the area of high mountains 2-3 km. 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 there is an area of high pressure, which contributes to the movement of air over the ridge. On the windward side, the rising air is cooled to the level of condensation (conventionally the lower boundary of the clouds) according to the dry adiabatic law (1°/100 m.), then according to the moist 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°/100m). As a result, on the leeward side of the ridge the clouds are washed away and the air reaches the foot of the mountains very dry and warm. During a foehn, difficult weather conditions are observed on the windward side of the ridge (fog, precipitation) and partly cloudy weather on the leeward side of the ridge, but here there is intense turbulence of the aircraft.
Bora is a strong gusty wind blowing from low coastal 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 region of Novorossiysk, in the north-eastern direction. 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 there is an area of low pressure, which creates large pressure gradients 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, extends 10-15 km deep into the sea, lasting up to 3 days, and sometimes more.
Very strong boron is formed on Novaya Zemlya. On Baikal, a bora-type wind is formed at the mouth of the Sarma River and is locally called “Sarma”.
Afghan - a very strong, dusty westerly or southwest wind in the eastern Karakum desert, up the valleys of the Amu Darya, Syrdarya and Vakhsh rivers. Accompanied by a dust storm and thunderstorm. Afghan emerges in connection with frontal invasions of cold into the Turan Lowland.
Local winds specific to certain areas have a major impact on aviation operations. Increased wind caused by the terrain features of a given area makes it difficult to pilot aircraft at low altitudes, and sometimes is dangerous for the flight.
When air flows over mountain ranges, leeward waves are formed in the atmosphere. They occur under the following conditions:
The presence of wind blowing perpendicular to the ridge, the speed of which is 50 km/h or more;
Wind speed increases with height;
The presence of inversion or isothermal layers from the top of the ridge at 1-3 km. Leeward waves cause intense vibration of aircraft. They are characterized by lenticular altocumulus clouds.
3.Vertical air movements
3.1 Causes and types of vertical air movements Vertical movements constantly occur in the atmosphere. They play a vital role in such atmospheric processes as the vertical transfer of heat and water vapor, the formation of clouds and precipitation, cloud dispersion, 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. More heated volumes of air, becoming lighter than the environment, rise upward, giving way to denser cold air falling down. The speed of upward movements can reach several meters per second, and in some cases 20-30 m/s (in powerful cumulus, cumulonimbus clouds).
Downdrafts have a smaller magnitude (~ 15 m/s).
Dynamic convection or dynamic turbulence is disordered vortex movements that occur during horizontal movement and friction of air against 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 areas on the windward side, or a slow, quiet “settling” of the air mass as a result of the general circulation of the atmosphere.
The convergence of air flows in the upper layers of the troposphere (convergence) of air flows in the upper layers of the atmosphere causes an increase in pressure near the ground and downward vertical movements in this layer.
The divergence of air flows at altitudes (divergence), on the contrary, leads to a drop in pressure near the ground and the rise of air upward.
Wave movements arise due to the difference in air density and the speed of its movement at the upper and lower boundaries of the inversion and isotherm layers. In the crests of the waves, upward movements are formed, in the valleys - downward movements. Wave movements in the atmosphere can be observed in the mountains on the leeward side, where leeward (standing) waves are formed.
When flying in an air mass where highly developed vertical currents are observed, the aircraft experiences bumps and surges, which complicate piloting. Large-scale vertical air flows can cause large vertical movements of the aircraft independent of the pilot. This can be particularly dangerous when flying at altitudes close to the aircraft's service ceiling, where updrafts can lift the aircraft to an altitude well above its ceiling, or when flying in mountainous areas on the leeward side of a ridge, where downdrafts can cause the aircraft to collide with the ground. .
Vertical air movements lead to the formation of cumulonimbus clouds that are dangerous for flight.
4.Clouds and precipitation
4.1 Causes of cloud formation. Classification.
Clouds are a visible accumulation of water droplets and ice crystals suspended in the air at some height above the earth's surface. Clouds are formed as a result of condensation (the transition of water vapor into a liquid state) and sublimation (the transition of water vapor directly into solid state) water vapor.
The main reason for the formation of clouds is the adiabatic (without exchange of heat with the environment) decrease in temperature in the rising humid air, leading to 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 sizes, the number of cloud particles per unit volume. Clouds are divided into ice, water and mixed (from crystals and droplets).
According to the international classification, clouds are divided into 10 main forms by appearance, and into four classes by height.
1. Upper tier clouds - 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 produce precipitation. Thickness is low: 200 m - 600 m. These include:
Cirrus clouds/Ci-cirrus/, looking like white threads, hooks. They are harbingers of worsening weather, the approach of a warm front;
Cirrocumulus clouds /Cc- cirrocumulus/ - small wings, small white flakes, ripples. The flight is accompanied by a slight bump;
Cirrostratus/Cs-cirrostratus/ have the appearance of a bluish uniform veil that covers the entire sky, a blurry disk of the sun is visible, and at night a halo circle appears around the moon. Flight in them may be accompanied by slight icing and electrification of the aircraft.
2. Middle-level clouds are located at an altitude of up to
2 km 6 km, 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. There is no precipitation, the flight is accompanied by bumpiness and icing;
High-layered / As-altostratus / are a continuous gray veil, thin high-layered have a thickness of 300-600 m, dense - 1-2 km. In winter, they receive heavy precipitation.
The flight is accompanied by icing.
3. Low-level clouds range from 50 to 2000 m, have a dense structure, poor visibility, and icing is often observed. These include:
Nimbostratus (Ns-nimbostratus), having a dark gray color, high water content, give abundant continuous precipitation. Below them, low fractonic rain/Frnb-fractonimbus/ clouds are formed 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 extent is 2-3 km, often merging with altostratus 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 stratocumulus clouds there is the greatest water content, and there is also an icing zone. As a rule, no precipitation falls from these clouds;
Stratus clouds (St-stratus) are a continuous, homogeneous 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. They make take-off and landing very difficult and cause drizzling precipitation. They can sink to the ground and turn into fog;
Fractured-stratus/St Fr-stratus fractus/ clouds have a lower limit of 100 m and below 100 m, they are formed as a result of the dispersion of radiation fog, precipitation does not fall from them.
4. Clouds of vertical development. Their lower boundary lies in the lower tier, the upper reaches the tropopause. These include:
Cumulus clouds (Cu cumulus) are dense cloud masses developed vertically with white dome-shaped tops and a flat base. Their lower limit is about 400-600 m and higher, the upper limit is 2-3 km, they do not produce precipitation. Flight in them is accompanied by bumpiness, 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; they do not produce precipitation. Flight in them is accompanied by moderate to strong turbulence, so entering these clouds is prohibited;
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 higher. They are associated with thunderstorms, showers, hail, intense icing, intense turbulence, squalls, tornadoes, and wind shears. At the top, cumulonimbus looks like an anvil, in the direction of which the cloud moves.
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 / Cu cong /
e) cumulonimbus/Cb/
2. Stratus arise as a result of upward sliding of warm moist air along the inclined surface of cold air, along flat frontal sections. Clouds of this type include:
a) cirrostratus/Cs/
b) highly layered/As/
c) nimbostratus/ Ns/
3. Wavy, occur during wave oscillations on inversion, isothermal layers and in layers with a small vertical temperature gradient.
These include:
a) altocumulus undulate
b) stratocumulus wavy.
4.2 Observations of clouds When observing clouds, the following is determined: the total number of clouds (indicated in octants), the number of lower-tier clouds, the shape of the clouds.
The height of the lower tier clouds is determined instrumentally using the IVO, DVO light locator with an accuracy of ±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.
During fog, precipitation or a dust storm, when the lower boundary of the clouds cannot be determined, the results of instrumental measurements are indicated in reports as vertical visibility.
At airfields equipped with landing approach systems, the height of the cloud base at values of 200 m and below is measured using sensors installed in the area of the BPRM. In other cases, measurements are made at working starts. When estimating the expected height of low clouds, the terrain is taken into account.
Over elevated places, clouds are located 50-60% lower than the difference in elevation of the points themselves. Over forested areas the clouds are always lower. Over industrial centers, where there are many condensation nuclei, the frequency of cloudiness increases. The lower edge of low clouds of stratus, stratus, fractus and nimbus is uneven, variable and experiences significant fluctuations within the range of 50-150 m.
Clouds are one of the most important meteorological elements affecting flights.
4.3 Precipitation Water droplets or ice crystals falling from clouds onto the Earth's surface are called precipitation. Precipitation usually falls from those clouds that are mixed in structure. For precipitation to occur, droplets or crystals must become larger to 2-3 mm. Enlargement of droplets occurs due to their merging upon collision.
The second process of enlargement 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 range from -10°C to 16°C and below. Based on the nature of precipitation, precipitation is divided into 3 types:
Overcast precipitation - falls over a long period of time and over a large area from nimbostratus and altostratus clouds;
Rainfall from cumulonimbus clouds, in a limited area, in a short period of time and in large quantities; The drops are larger, the snowflakes are flakes.
Drizzle - from stratus clouds, these are small droplets, the fall of which is not noticeable to the eye.
They are classified by type: rain, snow, freezing rain, passing through the ground layer of air with a negative temperature, drizzle, cereals, hail, snow grains, etc.
Precipitation includes: dew, frost, frost and snowstorms.
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 - it impairs horizontal visibility. Precipitation is considered heavy when visibility is less than 1000 m, regardless of the nature of the fall (cover, shower, drizzle). In addition, the water film on the cabin glass causes optical distortion of 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. Getting into the hail zone causes serious technical damage. When landing on a wet runway, the aircraft's runway length changes, which can lead to overrunning the runway. The jet of water thrown from 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:
Meteorological visibility range /MVD/ is the greatest distance from which, during daylight hours, a black object of sufficiently large size can be distinguished against the background of the sky near the horizon. At night, the distance to the most distant visible point source of light of a certain strength.
Meteorological visibility range is one of the meteorological elements important for aviation.
To monitor visibility at each aerodrome, a landmark diagram 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 of readings.
The averaging period is -10 minutes. for reports outside the airfield; 1 min. - for local regular and special reports.
Runway visual range (RVR) is 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 runway contours and its center line.
Visibility observations are made along the runway using instruments or on boards on which single light sources (60 W bulbs) are installed to assess visibility in the dark.
Since visibility can be very variable, visibility measuring devices are installed at the traffic control points of both courses and in the middle of the runway. The weather report includes:
a) with a runway length and less - the lesser of two values of 2000 m of visibility measured at both ends of the runway;
b) with a runway length of more than 2000 m - the lesser of two visibility values measured at the working start and the middle of the runway.
At airfields where OVI lighting systems are used with visibility of 1500 m or less at dusk and at night, 1000 m or less during the day, recalculation is carried out using tables into OVI visibility, which is also included in aviation weather. Recalculation of visibility into OMI visibility only at night.
In difficult weather conditions, especially when the plane is landing, it is important to know the oblique visibility. Slope visibility (landing) is the maximum slope distance along the descent glide path at which the pilot of a landing aircraft, when transitioning from instrument piloting to visual piloting, can detect the beginning of the runway. It is not measured, but assessed. The following dependence of oblique visibility on the magnitude of horizontal visibility at different cloud heights has been experimentally established:
When the height of the cloud base is less than 100 m and visibility is deteriorated due to haze and precipitation near the ground, oblique visibility is 25-45% of horizontal visibility;
When the height of the lower edge of the clouds is 100-150 m, it is equal to 40-50% of the horizontal; - at a height of the cloud boundary of 150-200 m, the inclined one 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 at the ground.
Fig.2 Effect of atmospheric haze on oblique visibility.
inversion
6. Basic atmospheric processes that cause weather Atmospheric processes observed over large geographical areas and studied using synoptic maps are called synoptic processes.
These processes are the result of the emergence, development and interaction of air masses, the divisions between them - atmospheric fronts and cyclones and anticyclones associated with these meteorological objects.
During pre-flight preparation, the aircraft crew must study the meteorological situation and flight conditions along the route, at departure and landing airports, at alternate airfields, paying attention to the main atmospheric processes that determine the weather:
On the state of air masses;
The location of pressure formations;
The position of atmospheric fronts relative to the flight route.
6.1 Air masses Large masses of air in the troposphere that have uniform weather conditions and physical properties are called air masses (AM).
There are 2 classifications of air masses: geographical and thermodynamic.
Geographical - depending on the areas of their formation, they are divided into:
a) arctic air (AV)
b) temperate/polar/air (HC)
d) tropical air (TV)
e) equatorial air (EA) Depending on the underlying surface over which this or that air mass was located for a long time, they are divided into marine and continental.
Depending on the thermal state (relative to the underlying surface), air masses can be warm or cold.
Depending on the conditions of vertical equilibrium, stable, unstable and indifferent stratification (state) of air masses are distinguished.
Stable VM is warmer than the underlying surface. There are no conditions for the development of vertical air movements, 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 isothermia are formed. The most favorable time for acquiring stability of VMs over the continent is during the day during the night, during the year during the year - winter.
The nature of the weather in UVM 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 to 1-2 km, partly cloudy above. In summer, partly cloudy weather or cumulus clouds with weak turbulence up to 500 m prevail in the UVM; visibility is somewhat impaired due to dust.
The UVM 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 (IAM) is a cold air mass in which favorable conditions are observed for the development of upward air movements, mainly thermal convection. When moving above the warm underlying surface, the lower layers of the cold water warm up, which leads to an increase in vertical temperature gradients to 0.8 - 1.5/100 m, as a consequence of this, to the intensive development of convective movements in the atmosphere. NVM is most active in the warm season. With sufficient moisture content in the air, cumulonimbus clouds up to 8-12 km, showers, hail, intramass thunderstorms, and squally winds develop. The daily cycle of all elements is well expressed. With sufficient humidity and subsequent clearing at night, radiation fogs can occur in the morning.
Flight in this mass is accompanied by bumpiness (Fig. 4).
During the cold season, there are no difficulties in flying in NVM. As a rule, it is clear, drifting snow, blowing snow, with northern and northeastern winds, and with a northwestern invasion of cold weather, clouds with a lower boundary of at least 200-300 m of the stratocumulus or cumulonimbus type with snow charges are observed.
Secondary cold fronts may occur in the NWM. The 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 surface of the earth towards the cold air.
The wind ahead of the front at the surface of the earth turns towards 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 orderly 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 due to bumpiness, because In this transition zone, two air masses move with different air densities, with different wind speeds and directions, which leads to the formation of vortices.
To assess the actual and expected weather conditions along the route or in the flight area, analysis of the position of atmospheric fronts relative to the flight route and their movement is of great importance.
Before departure, it is necessary to assess the activity of the front according to the following signs:
The fronts are located along the axis of the trough; the more pronounced the trough, the more active the front;
When passing through a front, the wind undergoes sharp changes in direction, convergence of current lines is observed, as well as changes in their speed;
The temperature on both sides of the front undergoes sharp changes, temperature contrasts amount to 6-10°C or more;
The pressure trend is not the same on both sides of the front; before the front it falls, behind the front it increases, 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 frontal zone, the more active the weather. On high-altitude maps, the front is expressed in thickening of isohypses and isotherms, in sharp contrasts in temperature and wind.
The front moves in the direction and at the speed of the gradient wind observed in the 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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MINISTRY OF HIGHER AND SECONDARY SPECIAL EDUCATION OF THE REPUBLIC OF UZBEKISTAN
TASHKENT STATE AVIATION INSTITUTE
Department: "Air Traffic Control"
Lecture notes
course "Aviation Meteorology"
TASHKENT - 2005
"Aviation meteorology"
Tashkent, TGAI, 2005.
The lecture notes include 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 pressure systems, are described. The issues of movement and evolution of atmospheric fronts, occlusion fronts, anticyclones, blizzards, types and forms of icing, thunderstorms, lightning, atmospheric turbulence and regular traffic - METAR, international aviation code TAF are considered.
Lecture notes were discussed and approved at a meeting of the Air Traffic Control Department
The method was approved by the FGA council at a meeting
Lecture No. 1
1. The subject and significance of meteorology:
2. Atmosphere, composition of the atmosphere.
3. The structure of the atmosphere.
Meteorology is 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. Weather is characterized by a combination of meteorological elements and phenomena, such as Atmosphere pressure, wind, humidity, air temperature, visibility, precipitation, clouds, icing, ice, fog, thunderstorms, blizzards, dust storms, tornadoes, various optical phenomena (halos, crowns).
Climate – long-term weather regime: characteristic of a given 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. Correct consideration of meteorological conditions in each specific case to best ensure the safety, economy and efficiency of flights depends on the pilot and dispatcher, on their ability to use meteorological information.
Flight and dispatch personnel must know:
What exactly is the influence of individual meteorological elements and weather phenomena on the operation of aviation;
Have a good understanding of the physical essence of atmospheric processes that create various weather conditions and their changes in time and space;
Know the methods of operational meteorological support of flights.
Organization of aircraft flights civil aviation GA to scale globe, and meteorological support for 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 issues of collection and dissemination of meteorological information for the benefit of civil aviation. Cooperation between these organizations is governed by special working agreements concluded between them. ICAO determines the meteorological information requirements arising from GA requests, and WMO determines the scientifically sound possibilities for meeting them and develops recommendations and regulations, as well as various guidance materials, mandatory for all its member countries.
Atmosphere.
Atmosphere is the air envelope of the earth, consisting of a mixture of gases and colloidal impurities ( dust, drops, crystals).
The earth is like the bottom of a huge ocean of air, and everything living and growing on it owes its existence to the atmosphere. It delivers the oxygen necessary for breathing, protects us from deadly cosmic rays and ultraviolet radiation from the sun, and also protects the earth's surface from extreme heating during the day and extreme cooling at night.
In the absence of an atmosphere, the surface temperature of the globe would reach 110° or more during the day, and at night it would sharply drop to 100° below zero. There would be complete silence everywhere, since sound cannot travel in emptiness, day and night would change instantly, and the sky would be completely black.
The atmosphere is transparent, but it constantly reminds us of itself: rain and snow, thunderstorms and blizzards, hurricanes and calm, heat and frost - all this is a manifestation of atmospheric processes occurring under the influence of solar energy and during the interaction of the atmosphere with the very surface of the earth.
Composition of the atmosphere.
Up to an altitude of 94-100 km. the percentage composition of the air remains constant - the homosphere (“homo” from Greek is the same); nitrogen – 78.09%, oxygen – 20.95%, argon – 0.93%. In addition, the atmosphere contains variable amounts 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 of the atmosphere (temperature distribution, air composition at altitudes, 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 for the structure of the atmosphere is a scheme based on the vertical temperature distribution. According to this scheme, the atmosphere is divided into five main spheres or layers: the troposphere, stratosphere, mesosphere, thermosphere and exosphere.
Interplanetary outer space | |||
Upper limit 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 at temperate latitudes. Control questions. 1. What does aviation meteorology study? 2. What functions are assigned to IKAO, WMO? |
|||
3. What functions are assigned to the Glavhydromet of the Republic of Uzbekistan?
4. Characterize the composition of the atmosphere.
Lecture No. 2.
1. The structure of the atmosphere (continued).
2. Standard atmosphere.
Troposphere – the lower part of the atmosphere to an average altitude of 11 km, where 4/5 of the total mass is concentrated atmospheric air and almost all water vapor. 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, and the formation of clouds and precipitation. There are 3 layers in the troposphere:
1. Boundary (friction layer) - from the ground to 1000 - 1500 km. This layer is affected by the thermal and mechanical effects of the earth's surface. The daily cycle of meteorological elements is observed. The lower part of the boundary layer, 600 m thick, is called the “ground layer”. The atmosphere above 1000 - 1500 meters is called the “free atmosphere layer” (without friction).
2. The middle layer is located from the upper boundary of the boundary layer to a height of 6 km. There is almost no influence of the earth's surface here. Weather conditions depend on atmospheric fronts and the vertical balance of air masses.
3. The top layer lies above 6 km. and extends to the tropopause.
Tropopause – transition layer between the troposphere and stratosphere. The thickness of this layer ranges from several hundred meters to 1 – 2 km, and average temperature 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 delaying layer for vertical air movements. When crossing the tropopause at the flight level, changes in temperature, changes in moisture content and air transparency can be observed. The minimum wind speed is usually located in the tropopause zone or its lower boundary.
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%, others account for less than 0.01%.
Air is characterized by the following parameters: pressure, temperature and humidity.
International standard atmosphere.
Temperature gradient.
The air is heated by the ground, and density decreases with height. The combination of these two factors creates a normal situation where air is warmer at the surface and gradually cools with height.
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, winter has a lower cloud base and distribution.
Water can be in three forms: solid, liquid, gas. Water has a high heat capacity. In the solid state it has a lower density than in the liquid state. As a result, it softens the climate on a planetary scale. IN gaseous state 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 the horizontal plane. This imbalance appears due to differences in air temperatures in neighboring areas or vertical air circulation in different areas. The root cause is solar heating of the surface.
Wind is named by the direction from which it blows. For example: northern blows from the north, mountain blows from the mountains, valley blows into 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 hemisphere - to the left. The Coriolis effect is strong at the poles and disappears at the equator. The Coriolis effect is caused by the rotation of the Earth under moving objects. This is not some real strength, this is the illusion of right rotation for all freely moving bodies. Rice. 32
Air masses.
An air mass is air that has the same temperature and humidity over an area of at least 1600 km. An air mass can be cold if it formed in the polar regions, warm - from the tropical zone. It can be marine or continental in humidity.
When a CVM arrives, the ground layer of air is heated by the ground, increasing instability. When the TBM arrives, the surface 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 moves forward, it is a cold front. If warm air moves forward, it is a warm front. Sometimes air masses move until they are stopped by 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
Types of clouds.
There are only three main types of clouds. These are stratus, cumulus and cirrus i.e. stratus (St), cumulus (Cu) and cirrus (Ci).
stratus cumulus cirrus Fig. 35
Classification of clouds by height:
Rice. 36
Lesser known clouds:
Haze - Forms when warm, moist air moves ashore, or when the ground radiates heat into a cold, moist layer at night.
Cloud cap - forms above the peak when dynamic updrafts occur. Fig.37
Flag-shaped clouds - form behind mountain peaks when strong wind. Sometimes it consists of snow. Fig.38
Rotor clouds - can form on the leeward side of the mountain, behind the ridge in strong winds and have the form of long ropes located along the mountain. They form on the ascending sides of the rotor and are destroyed on the descending ones. Indicates severe turbulence. Fig. 39
Wave or lenticular clouds - are formed by wave movement of air during strong winds. They do not move relative to the ground. Fig.40
Rice. 37 Fig. 38 Fig.39
Ribbed clouds are very similar to ripples on 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 the inversion layer. Rice. 42
Rice. 40 Fig. 41 Fig. 42
Cloud formation.
Clouds consist of countless microscopic particles of water of various sizes: from 0.001 cm in saturated air to 0.025 with ongoing condensation. The main way clouds form in the atmosphere is by cooling moist air. This occurs when the air cools as it rises.
Fog forms in cooling air from contact with the ground.
Updrafts.
There are three main reasons why updrafts occur. 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 rate of rise depends on the strength of the wind and the steepness of the slope, and can reach up to 30 m/s. Thermal flow occurs when warmer air rises and is heated by the earth's surface on sunny days. 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. Let’s assume that the rising air cools in a certain way, for example, 1 0 C/100 m. But the dew point drops only by 0.2 0 C/100 m. Thus, the dew point and the temperature of the rising air approach 0.8 0 C/100 m. When they equalize, clouds will form. Meteorologists use dry and wet bulb thermometers to measure ground and saturation temperatures. From these measurements you can calculate the cloud base. 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 2000 m.
Life of the clouds.
During their development, clouds 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 until it disintegrates into an amorphous mass. However, often the clouds do not break up as quickly. This happens when the air humidity at the level of the clouds and the humidity of the cloud coincide. 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 pilot's lexicon.
Continued thermality can also fuel individual clouds, increasing their lifetime by more than 0.5 hours. In fact, thunderstorms are long-lived clouds formed by thermal currents.
Precipitation.
For precipitation to occur, two conditions are necessary: prolonged updrafts and high humidity. Water droplets or ice crystals begin to grow in the cloud. When they get big, they start to fall. It is snowing, raining or hailing.
Dangerous weather phenomena for aviation.
Visibility-impairing phenomena
Fog ()- this is an accumulation of water droplets or crystals suspended in the air near the earth's surface, impairing horizontal visibility of less than 1000 m. At a visibility range of 1000 m to 10,000 m, this phenomenon is called haze (=).
One of the conditions for the formation of fog in the ground 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 mists 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 several 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 an anticyclone, in saddles:
They appear first in lowlands, ravines, and floodplains. As the sun rises and the wind increases, radiation fogs dissipate and sometimes turn into a thin layer of low clouds. Radiation fogs are especially dangerous for aircraft landing.
Advective fogs are formed by the movement of a warm, moist, airy mass over the cold underlying surface of a continent or sea. They can be observed in wind speeds of 5 – 10 m/sec. 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.
Advection-radiation fogs are formed under the influence of two factors: movement 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 duration than advective fogs. They are formed under the same synoptic situation as advective fogs (warm sector of the cyclone, western periphery of the anticyclone), most characteristic of the autumn-winter period.
Mists of the slopes occur when moist air rises calmly along mountain slopes. In this case, the air expands adiabatically 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 a fog of evaporation 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 (furnace) mists are formed in winter at low temperatures in areas of Siberia and the Arctic, usually 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 firebox or stoves. They quickly acquire significant density. During the day, as the air temperature rises, they collapse and weaken, but intensify again in the evening. Sometimes such fogs last for several days.
Frontal fogsare formed in the zone of slowly moving and stationary fronts (warm and warm occlusion fronts) at any (more often in cold) time of day and year.
Prefrontal fogs are formed due to the saturation of cold air located under the frontal surface with moisture. Conditions for the formation of prefrontal fog 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 that forms during the passage of a front is a cloud system that has spread to the surface of the earth* This is especially common when the front passes over higher elevations.
The conditions of formation of behind-frontal fog are practically no different from the conditions of formation of advective fogs.
Blizzard - snow transfer strong winds above the surface of the earth. The intensity of a snowstorm depends on wind speed, turbulence and snow conditions. A snowstorm can impair visibility, make landing difficult, and sometimes prevent aircraft from taking off and landing. During severe, prolonged snowstorms, the performance of airfields deteriorates.
There are three types of snowstorms: drifting snow, blowing snow and general snowstorm.
Drifting snow() - snow transport by wind only at the surface of the snow cover up to a height of 1.5 m. Observed in the rear of the cyclone and the front part of the anticyclone with a wind of 6 m/sec. and more. It causes swelling on the runway and makes it difficult to visually determine the distance to the ground. The horizontal visibility of drifting snow does not impair.
Blizzard() - the transfer of snow by the wind along the earth's surface with a rise to a height of more than two meters. Observed with winds of 10-12 m/sec or more. The synoptic situation is the same as with drifting snow (the rear of the cyclone, the eastern periphery of the anticyclone). Visibility during a blowing snow, it depends on the wind speed. If the wind is II-I4 m/sec., then the horizontal visibility can be from 4 to 2 km, with a wind of 15-18 m/sec. - from 2 km up to 500 m and with a wind of more than 18 m/sec. - less than 500 m.
General snowstorm () - snow falling from the clouds and simultaneously being transported by the wind along the earth's surface. It usually starts when there is wind 7 m/sec. and more. Occurs on atmospheric fronts. The height extends to the bottom of the clouds. In strong winds and heavy snowfall, visibility sharply worsens both horizontally and vertically. Often during takeoff and landing in a general snowstorm, the aircraft becomes electrified, distorting instrument readings
Dust storm() - transfer of large quantities of dust or sand by strong winds. It is observed in deserts and places with arid climates, but sometimes occurs in temperate latitudes. The horizontal extent of a dust storm can be. from a few hundred meters to 1000 km. The vertical height of the atmospheric dust layer varies from 1-2 km (dusty or sandy drifting snow) to 6-9 km (dust storms).
Main reasons for education 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 sudden changes in the pressure 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, dust rises to great heights and is transported over considerable distances.
Haze() - cloudiness of the air caused by particles of dust and smoke suspended in it. In severe haze, visibility can be reduced to hundreds and tens of meters. More often, visibility in darkness is more than 1 km. Observed in steppes and deserts: maybe after dust storms, forest and peat fires. Haze over large cities is associated with air pollution from 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 Civil Aviation Regulations, are classified as dangerous meteorological phenomena for flights.
Even with light icing, the aerodynamic qualities of the aircraft change significantly, the weight increases, engine power decreases, and the operation of control mechanisms and some navigation instruments is disrupted. Ice released from icy surfaces can get into the engines or onto the casing, which leads to mechanical damage. Icing on the cockpit windows impairs visibility and reduces visibility.
The complex impact of icing on an aircraft poses a threat to flight safety, and in some cases can lead to an accident. Icing is especially dangerous during takeoff and landing as a concomitant phenomenon in the event of failures of individual aircraft systems.
The process of aircraft icing depends on many meteorological and aerodynamic variable factors. The main cause of icing is the freezing of supercooled water droplets when they collide with an aircraft. The manual for meteorological support of flights provides for a conditional gradation of icing intensity.
The intensity of icing is usually measured by the thickness of ice growth per unit time. Typically thickness is measured in millimeters of ice deposited on various parts Sun per minute (mm/min). When measuring ice deposits on the leading edge of a 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 weak degree of icing, 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 an aircraft into an icing zone without the anti-icing systems turned on is dangerous. If the degree of icing is severe, systems and means cannot cope with the growing ice and an immediate exit from the icing zone is necessary.
Aircraft icing occurs in clouds located from the ground to the height 2-3 km. At subzero 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 clouds, 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 heavy precipitation on the warm front, the probability of icing is low.
The most intense icing can occur when flying under clouds in an area of freezing rain and/or drizzle.
Icing is unlikely in upper-level clouds, but it should be remembered that intense icing is possible in cirrostratus and cirrocumulus clouds if they remain after the destruction of thunderstorm clouds.
Icing was possible at temperatures from -(-5 to -50°C in clouds, fog and precipitation. As statistics show, the largest number of cases of icing. Sun is observed at air temperatures from 0 to -20°C, and especially from 0 to - 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 due to icing ( N.S.) The radius of raindrops is several mm, so even light freezing rain can very quickly lead to severe icing.
Drizzle (St ) at negative temperatures during a long flight also leads to severe icing.
Sleet (NS) , WITH B ) - usually falls out in flakes and is very dangerous due to strong icing.
Icing in “dry snow” or crystalline clouds is unlikely. However, icing of jet engines is possible even in such conditions - the surface of the air intake can cool 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 shape of aircraft icing:
Microphysical structure of clouds (whether they consist only of supercooled drops, only of crystals, or have a mixed structure, spectral size of drops, water content of the cloud, etc.);
- temperature of the air flow;
- speed and flight mode;
- shape and size of parts;
As a result of the influence of all these factors, the types and forms of ice deposits on the surface of aircraft are extremely diverse.
The type of ice deposits is divided into:
Transparent or glassy, it is most often formed when flying in clouds containing mainly large drops, or in an area of supercooled rain at air temperatures from 0 to -10 ° C and below.
Large drops, hitting the surface of the aircraft, spread and gradually freeze, first forming a smooth, ice film that almost does not distort the profile of the bearing surfaces. With significant growth, the ice becomes lumpy, which makes this type of deposit, which has the highest density, very dangerous due to the increase in weight and significant changes in the aerodynamic characteristics of the aircraft;
Matt 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 a rough surface, the density of which is slightly less than transparent. This type of deposit greatly distorts the shape of parts of the aircraft flown by the air flow, adheres firmly to its surface and reaches a large mass, therefore it is the most dangerous;
White or coarse, in fine-droplet clouds of layered 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. Coarse ice has weak adhesion to aircraft surfaces and is easily separated during vibrations, but during a long flight in an icing zone, the accumulating ice, under the influence of mechanical air shocks, becomes compacted and acts as matte ice;
Drizzle is formed when there are small supercooled droplets with a large number of ice crystals in the clouds at a temperature of -10 to -15°C. Frost deposits, uneven and rough, adhere weakly to the surface and are easily dislodged by air flow when vibrating. Dangerous during a long flight in an icing zone, reaching great 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 when BC suddenly enters from cold layers to warm ones. It is a light fine-crystalline coating that disappears when the sun temperature equalizes the air temperature. Frost: not dangerous, but can be a stimulator of severe icing when the aircraft enters the clouds.
The shape of ice deposits depends on the same reasons as the types:
- profile, having the appearance of the profile on which the ice was deposited; most often made of transparent ice;
- wedge-shaped is a clip on the front wing made of white coarse ice;
The groove-shaped has a reverse V appearance at the leading edge of the streamlined profile. The recess is obtained due to kinetic heating and thawing of the central part. These are lumpy, rough growths from frosted ice. This is the most dangerous type of icing
- barrier or mushroom-shaped - a roller or separate streaks behind the heating zone of transparent and matte ice;
The shape largely depends on the profile, which changes along the entire length of the wing or propeller blade, so different forms of icing can be observed simultaneously.
Effect of high speeds on icing.
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 thus the intensity of icing increases;
As 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 C 4 7 10 13 17 21 22
Calculations show that kinetic heating in clouds is 60^ of kinetic heating in dry air (heat loss due to 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 of a dangerous form of icing.
Type of ground icing.
Various types of ice may be deposited on the surface of aircraft on the ground at sub-zero temperatures. According to the conditions of formation, all types of ice are divided into three main groups.
The first group includes frost, hoarfrost and solid deposits formed as a result of the direct transition of water vapor into ice (sublimation).
Frost mainly covers the upper horizontal surfaces of the aircraft when they are cooled to subzero temperatures on clear, quiet nights.
Frost forms in moist air, mainly on the protruding windward parts of the aircraft, in frosty weather, fog and light winds.
Frost and frost adhere weakly to the surface of the aircraft 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), falling raindrops spread over the surface of the aircraft and freeze in the form of transparent ice.
At lower temperatures, the drops quickly freeze and frosted ice forms. These types of ice can reach large sizes and adhere firmly to the surface of the aircraft.
The third group includes types of ice deposited on the surface of an aircraft when falling rain, sleet, or fog drops freeze. These types of ice do not differ in 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.
From the above it follows that before takeoff the aircraft must be thoroughly cleared of ice. You need to check the condition of the aircraft surface especially carefully at night at subzero air temperatures. It is prohibited to take off on an airplane whose surface is covered with ice.
Features of helicopter icing.
Physico-meteorological conditions for helicopter icing are similar to those for airplanes.
At temperatures from 0 to ~10°C, ice is deposited on the propeller blades mainly at the axis of rotation 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 speed, the intensity of propeller icing 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 become completely icy, and the intensity of ice growth at the leading edge is proportional to the radius. When the main rotor becomes icy, strong vibration occurs, affecting the controllability of the helicopter, the engine speed drops, and the speed cannot be increased to the previous value. restores the lifting force of the propeller, which can lead to 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. Usually observed at temperatures from 0 to -5°C, less often at lower temperatures: (up to -16°). Ice forms in the zone of a warm front, most often in the zone of the occlusion front, stationary front and in the warm sector of the cyclone.
Black ice – ice on the earth's surface that forms after a thaw or rain as a result of the onset of cold weather, 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 approved aircraft. 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 data on actual weather and the forecast, determine the most favorable flight levels.
Before entering cloudy areas where icing is likely, anti-icing systems should be turned on, since delay in turning on significantly reduces their effectiveness.
If icing is severe, de-icing agents are not effective, so the flight level should be changed in consultation with the traffic service.
In winter, when the cloud layer with an isotherm from -10 to -12°C is located close to the earth's surface, it is advisable to go up to the temperature region below -20°C, leaving the rest of the year, if the altitude allowance, is down to the positive region. temperatures
If the icing does not disappear when changing flight levels, you must return to the departure point or land at the earliest alternate airfield.
Difficult situations most often arise due to pilots underestimating the danger of even mild icing
THUNDERSTORMS
A thunderstorm is a complex atmospheric phenomenon in which multiple electrical discharges are observed, accompanied by a sound phenomenon - thunder, as well as rainfall precipitation.
Conditions necessary for the development of intramass thunderstorms:
instability of the air mass (large vertical temperature gradients, at least up to an altitude of about 2 km - 1/100 m before the condensation level and - > 0.5°/100 m above the condensation level);
High absolute air humidity (13-15 mb. in the morning);
High temperatures at the surface of the earth. The zero isotherm on days with thunderstorms lies at an altitude of 3-4 km.
Frontal and orographic thunderstorms develop mainly due to the forced rise of air. Therefore, these thunderstorms in the mountains begin earlier and end later, form on the windward side (if these are high mountain systems) and are stronger than in flat areas for the same synoptic position.
Stages of development of a thundercloud.
The first is the growth stage, which is characterized by a rapid rise to the top and maintenance appearance droplet cloud. During thermal convection during this period, cumulus clouds (Ci) turn into powerful cumulus clouds (Ci conq/). In clouds b, only upward air movements from several m/s (Ci) to 10-15 m/s (Ci conq/) are observed under the clouds. Then the upper layer of clouds moves 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 above 0° appear - severe icing.
Second - stationary stage , characterized by the cessation of intensive upward growth of the cloud top and the formation of an anvil (cirrus clouds, often elongated in the direction of movement of the thunderstorm). These are cumulonimbus clouds in a state of maximum development. Turbulence is added to vertical movements. The speed of ascending flows can reach 63 m/s, and descending flows ~ 24 m/s. In addition to showers, there may be hail. At this time, electrical discharges - lightning - are formed. There may be squalls and tornadoes under the cloud. The upper limit of the clouds reaches 10-12 km. In the tropics, individual thunderstorm cloud tops develop to a height of 20-21 km.
The third is the stage of destruction (dissipation), during which the droplet-liquid part of the cumulonimbus cloud is washed away, and the top, which has turned into a cirrus cloud, often continues to exist independently. At this time, electrical discharges stop, precipitation weakens, and downward air movements predominate.
During the transition seasons and during the winter development stage, all processes of a thundercloud are much less pronounced and do not always have clear visual signs
According to the Civil Aviation Administration, a thunderstorm over an airfield is considered if the distance to the thunderstorm is No. km. and less. A 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 observations of thunderclouds show that a positive charge is usually formed at the top of the cloud, a negative charge is formed in the middle part, and there can be both positive and negative charges at the bottom. The radius of these areas with opposite charges varies from 0.5 km to 1-2 km.
Punching tension electric field for dry air it is I million v/m. In clouds, for lightning discharges to occur, it is enough for the field strength to reach 300-350 thousand V/m. (measured values during experimental flights) Apparently, these or close to them field strength values represent the strength of the beginning of the discharge, and for its propagation, strengths that are much lower, but covering a large space, are sufficient. The frequency of discharges in a moderate thunderstorm is about 1/min, and in an intense thunderstorm – 5–10/min.
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 advances in “Jumps” with a length of 10-200 m. Along the ionized lightning channel, a return stroke develops from the surface of the earth, which transfers the main lightning charge. The current strength reaches 200 thousand A. Usually following the first step leader after hundredths of a second. development occurs along the same channel of the arrow-shaped leader, after which the second return blow occurs. This process can be repeated many times.
Linear lightning are formed most often, their length is usually 2-3 km (between clouds 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 about 1 sec. You cannot mix flat lightning with lightning. Lightning strikes are discharges of distant thunderstorms: lightning is not visible and thunder is not heard, only the lighting of the 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 inside buildings and aircraft during flight. Often, without causing harm, it goes away unnoticed, but sometimes it explodes with a deafening crash. The phenomenon can last from a few seconds to several minutes. This is a little studied physicochemical 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 expansion of air along the lightning path. In addition, during the discharge, water molecules decompose into their component parts with the formation of “explosive gas” - “channel explosions”. Since the sound from different points of the lightning path does not arrive simultaneously and is reflected many times from clouds and the surface of the earth, thunder has the character of long peals. Thunder is usually heard at a distance of 15-20 km.
hail- This is precipitation falling from the Earth in the form of spherical ice. If above the 0° level the maximum increase in upward flows exceeds Yum/sec, and the top of the cloud is located in the temperature zone - 20-25°, then ice formation is possible in such a cloud. A hail center forms above the level of maximum speed of upward flows, and here the accumulation of large drops and the main growth of hailstones occurs. In the upper part of the cloud, when crystals collide with supercooled drops, snow grains (embryos of hailstones) 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 falling out of the cloud is about 15 minutes. The width of the “hail road” can be from 2 to 6 km, length 40-100 km. The thickness of the layer of fallen hail sometimes exceeds 20 cm. The average duration of hail is 5 10 minutes, but in some cases it may be longer. Most often, hailstones with a diameter of 1-3 cm are found, but they can be up to 10 cm or more. .Hail is detected not only under a cloud, but can damage aircraft at high altitudes (up to an altitude of 13,700 m and up to 15-20 km from a thunderstorm).
Hail can break the glass of the pilot's cockpit, destroy the radar fairing, pierce or make dents in the casing, and damage the leading edge of the wings, stabilizer, and antennas.
Heavy rain shower sharply reduces visibility to less than 1000 m, can cause engines to shut down, degrades the aerodynamic qualities of the aircraft and can, in some cases, without any wind shear, reduce the lifting force during approach or takeoff by 30%.
Squall- a sharp increase (more than 15 m/s) of 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 thunderstorms, then in the front part the width of the squall zone can reach 30 km. Swirls of dust near the surface of the earth in the region of a cumulonimbus cloud are a visual sign of a “front of air gusts” (squalls). Squalls are associated with intramass and frontal, highly developed NE clouds.
Squall gate- a vortex with a horizontal axis in the front part of a thundercloud. This is a dark, hanging, rotating cloud bank 1-2 km before a continuous curtain of rain. Usually the vortex moves at an altitude 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 looks like a dark cloud column with a diameter of several tens of meters. 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/sec with a strong upward component. The pressure drop inside a tornado can be 40-100 mb. Tornadoes can cause catastrophic destruction, sometimes resulting in loss of life. The tornado should be bypassed at a distance of at least 30 km.
Turbulence near thunderclouds has a number of features. It becomes increased 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, with the greatest intensity observed in the rear part. Even after a cloud has completely collapsed, the area of the atmosphere where it was located remains more disturbed, that is, turbulent zones live longer than the clouds with which they are associated.
Above the upper boundary of a growing cumulonimbus cloud, upward movements at a speed of 7-10 m/sec create a layer of intense turbulence 500 m thick. And above the anvil, downward air movements are observed at a speed of 5-7 m/sec, 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 (over the sea these phenomena are observed most often in winter and at night). Intramass 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 invasion (advection) of cold air, which in the lower half of the troposphere is very unstable and thermal and dynamic turbulence develops well in it;
- orographic- are formed in mountainous areas, develop more often on the windward side and are stronger and longer lasting (start earlier, end later) than in flat areas under the same weather conditions on the windward side.
Frontal thunderstorms are formed at any time of the day (depending on which front is located in a given area). In summer, almost all fronts (except stationary ones) produce thunderstorms.
Thunderstorm centers in the frontal zone sometimes have zones up to 400-500 km long. On major slow-moving fronts, thunderstorms may be masked by upper- and mid-level 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 thunderstorms, intensify on the windward side. Fronts on the periphery of cyclones, old eroding occlusion fronts, and surface fronts give rise to 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 rarely form in temperate latitudes, only in the zone of main, active atmospheric fronts that separate air masses with a large temperature contrast and move at high speed.
Thunderstorms are observed visually and instrumentally. Visual observations have a number of disadvantages. A weather observer, whose observation radius is limited to 10-15 km, records the presence of a thunderstorm. At night, in difficult meteorological conditions, it is difficult to determine cloud shapes.
For instrumental observations of thunderstorms, weather radars (MRL-1, MRL-2. MRL-5), thunderstorm azimuth direction finders (GAT), panoramic thunderstorm recorders (PRG) and lightning markers included in the KRAMS complex (comprehensive radio-technical automatic weather station) are used. .
MRL give the most full information about the development of thunderstorm activity within a radius of up to 300 km.
Based on reflectivity data, it determines the location of the thunderstorm source, its horizontal and vertical dimensions, speed and direction of displacement. Based on observational data, radar maps are compiled.
If thunderstorm activity is observed or predicted in the flight area, during the pre-flight preparation period the flight control center is obliged to carefully analyze the meteorological situation. Using MRL maps, determine the location and direction of movement of thunderstorm (shower) centers, their upper limit, outline detour routes, safe echelon. It is necessary to know the symbols of thunderstorm weather phenomena and heavy rainfall.
When approaching a zone of lightning activity, the pilot-in-command must use the radar to assess in advance the possibility of flying through this zone and inform the controller about the flight conditions. For safety, a decision is made to bypass thunderstorm centers or fly to an alternate airfield.
The dispatcher, using information from the meteorological service and weather reports from the aircraft, is obliged to inform crews about the nature of thunderstorms, their vertical power, directions and speed of displacement and give recommendations on leaving the area of thunderstorm activity.
If powerful cumulus and cumulonimbus clouds are detected in flight by the BRL, it is allowed to bypass these clouds at a distance of at least 15 km from the nearest border of illumination.
The intersection of frontal clouds with individual thunderstorm centers can occur in the place where the distance between
the boundaries of flare on the BRL screen are at least 50 km.
Flight over the upper limit of powerful cumulus and cumulonimbus clouds is permitted with an elevation of at least 500 m above them.
Aircraft crews are prohibited from deliberately entering powerful cumulus and cumulonimbus clouds and areas of heavy rainfall.
When taking off, landing and the presence of thick cumulus, cumulonimbus clouds in the airfield area, the crew: is obliged to inspect the airfield area with the help of radar, assess the possibility of takeoff, landing and determine the procedure for avoiding thick cumulus, cumulonimbus clouds and areas of heavy rainfall precipitation.
Flight under cumulonimbus clouds is permitted only during the day, outside the zone of heavy rainfall, if:
- aircraft flight altitude above the terrain is at least 200 m and in mountainous areas at least 600 m;
- vertical distance from the aircraft to the bottom of the clouds is at least 200 m.
Electrification of aircraft and discharge of static electricity.
The phenomenon of aircraft electrification is 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 greater, the larger the aircraft and its speed, as well as the greater the number of moisture particles contained in unit volume of air. Charges can also appear on the aircraft when flying near clouds that have electrical charges. Highest density charges are noted on the sharp convex parts of the aircraft, and an outflow of electricity in the form of sparks, luminous crowns, and a crown is observed.
Most often, aircraft electrification is observed when flying in crystalline clouds of the upper tier, as well as mixed clouds of the middle and lower tiers. Charges on the aircraft can also appear when flying near clouds that have electrical charges.
In some cases, the electric charge that an aircraft has is one of the main causes of aircraft being damaged by lightning in nimbostratus clouds at altitudes of 1500 to 3000 m. The thicker the clouds, the greater the likelihood of damage.
For electrical discharges to occur, it is necessary that a non-uniform electric field exist in the cloud, which is largely determined by the phase state of the cloud.
If the electric field strength between volumetric electric charges in the cloud is less than a critical value, then no discharge occurs between them.
When flying near an airplane cloud that has its own electrical charge, the voltage fields can reach a critical value, then an electrical discharge occurs into the aircraft.
As a rule, lightning does not occur in nimbostratus clouds, although they contain opposite volumetric electric charges. The electric field strength is not sufficient to cause lightning. But if there is an aircraft with a large surface charge near such a cloud or in it, then it can cause a discharge on itself. Lightning originating in a cloud will hit the sun.
A method for predicting dangerous damage to aircraft by electrostatic discharges outside zones of active thunderstorm activity has not yet been developed.
To ensure flight safety in nimbostratus clouds, if the aircraft becomes highly electrified, the flight altitude should be changed in agreement with the dispatcher.
Damage to aircraft by atmospheric electrical discharge more often occurs in cloud systems of cold and secondary cold fronts, in autumn and winter more often than in spring and summer.
Signs of strong electrification of aircraft are:
Noises and crackling in headphones;
Random oscillation of radio compass needles;
Sparking on the glass of the cockpit and the glow of the tips of the wings at night.
Atmospheric turbulence.
The turbulent state of the atmosphere is a state in which disordered vortex movements of various scales and different speeds 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 disrupted. Additional accelerations occur, causing the aircraft to sway.
The main causes of air turbulence are contrasts in temperatures and wind speeds that arise for some 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, friction of the flow against 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, dry ones heat up the most. sandy soils, less - land areas covered with grass, forests, and even less - water surfaces. Unevenly heated areas of land cause uneven heating of the layers of air adjacent to the ground, and ascending movements of unequal 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 weak or moderate turbulence. It spreads from the ground to an altitude of 2500m. Maximum turbulence occurs in the afternoon hours.
If the air is humid, then with: rising currents, cumulus-shaped clouds form (especially with an unstable air mass). In this case, the upper boundary of the turbulence is the cloud's top.
When inversion layers intersect in the tropopause zone and the inversion zone above the earth's surface.
At the boundary of such layers, in which the winds often have different directions and speeds, wave-like movements arise, ..^ causing weak or moderate chatter.
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 a jet stream zone due to differences in speed gradients;
When flying over mountainous terrain, orographic bumps form on the leeward side of mountains and hills. . . On the windward side there is a uniform upward flow, and the higher the mountains and the less steep the slopes, the farther from the mountains the air begins to rise. With a ridge height of 1000 m, upward 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, the speed of the ascending currents increases due to the mountain-valley effect. But when the slopes are steep and the wind is strong, turbulence will also form inside the updraft, and the flight will occur in a turbulent 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 wind.
On the leeward side of the ridge, the plane, 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 an air flow crosses a mountain range, leeward 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 wind speed increases with height:
If the transshipment air is rich in moisture, then lentil-shaped clouds form in the part where rising air currents are observed.
In the case when through mountain range dry air passes through, cloudless leeward waves are formed and the pilot can completely unexpectedly encounter strong bumps (one of the cases of TJN).
In zones of convergence and divergence of air flows with a sharp change in flow direction.
In the absence of clouds, this will be the conditions for the formation of CN (clear sky turbulence).
The horizontal length of a nuclear power plant can be several hundred km. A
several hundred meters thick. hundred meters. Moreover, there is such a dependence: the more intense the turbulence (and the associated turbulence of the aircraft), the thinner the layer thickness.
When preparing for a flight, using the configuration of isohypses on the AT-400 and AT-300 maps, you can determine areas of possible aircraft roughness.
Wind shear.
Wind shear is a change in the direction and (or) speed of wind in space, including upward and downward air currents.
Depending on the orientation of points in space and the direction of movement of the aircraft relative to H1Sh, vertical and horizontal wind shears are distinguished.
The essence of the influence 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 danger is posed by wind shear when the aircraft is in landing configuration on the glide path.
Wind shear intensity criteria (recommended by the working group
(ICAO).
| Wind shear intensity is a qualitative term | Vertical wind shear – upward and downward flows at 30 m height, horizontal wind shear at 600 m, m/sec. | Effect 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 30-meter layer) in the surface layer, so the wind shear values are recalculated to the 100-meter layer:
0-6 m/sec. - weak; 6 -13 m/sec. - moderate; 13 -20 m/sec, strong
20 m/sec. very strong
Horizontal (lateral) wind shears caused by... sharp changes in wind direction with height cause a tendency for the aircraft to shift from the centerline of the upper propeller. When landing an aircraft, this is a challenge ^ there is a danger of the ground touching the runway, during takeoff the layout
increase the lateral displacement beyond the safe climb sector.
Wertsch
Vertical wind shear in prizog 
When the wind increases sharply with altitude, positive wind shear occurs.
Aviation meteorology
Aviation meteorology
(from the Greek met(éö)ra - celestial phenomena and logos - word, doctrine) - an applied discipline that studies the meteorological conditions in which aircraft operate, and the impact of these conditions on the safety and efficiency of flights, developing methods for collecting and processing meteorological information, preparation of forecasts and meteorological support for flights. As aviation develops (the creation of new types of aircraft, the expansion of the range of altitudes and flight speeds, the scale of territories for flight operations, the expansion of the range of tasks solved with the help of aircraft, etc.), aviation is faced with. new tasks are being set. The creation of new airports and the opening of new air routes requires climatic research in the areas of proposed construction and in the free atmosphere along the planned flight routes in order to select optimal solutions to the tasks. Changing conditions around existing airports (as a result economic activity human or under the influence of natural physical processes) requires constant study of the climate of existing airports. The close dependence of weather near the earth's surface (aircraft takeoff and landing zone) on local conditions requires special research for each airport and the development of methods for forecasting takeoff and landing conditions for almost every airport. The main tasks of M. a. as an applied discipline - increasing the level and optimizing flight information support, improving the quality of meteorological services provided (the accuracy of actual data and the accuracy of forecasts), increasing efficiency. The solution to these problems is achieved by improving the material and technical base, technologies and observation methods, in-depth study of the physics of the formation processes of weather phenomena important for aviation and improving methods for forecasting these phenomena.
Aviation: Encyclopedia. - M.: Great Russian Encyclopedia. Editor-in-Chief G.P. Svishchev. 1994 .
See what “aviation meteorology” is in other dictionaries:
Aviation meteorology- Aviation meteorology: an applied discipline that studies the meteorological conditions of aviation, their impact on aviation, forms of meteorological support for aviation and methods of protecting it from adverse atmospheric influences...... ... Official terminology
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aviation meteorology Encyclopedia "Aviation"
aviation meteorology- (from the Greek metéōra celestial phenomena and logos word, doctrine) applied discipline that studies the meteorological conditions in which aircraft operate, and the influence of these conditions on the safety and efficiency of flights,... ... Encyclopedia "Aviation"
See Aviation meteorology... Great Soviet Encyclopedia
Meteorology- Meteorology: the science of the atmosphere about its structure, properties and physical processes occurring in it, one of the geophysical sciences (the term atmospheric sciences is also used). Note The main disciplines of meteorology are dynamic, ... ... Official terminology
The science of the atmosphere, its structure, properties and processes occurring in it. Refers to geophysical sciences. Based on physical research methods (meteorological measurements, etc.). Within meteorology there are several sections and... Geographical encyclopedia
aviation meteorology- 2.1.1 aviation meteorology: An applied discipline that studies the meteorological conditions of aviation, their impact on aviation, forms of meteorological support for aviation and methods of protecting it from adverse atmospheric influences.… … Dictionary-reference book of terms of normative and technical documentation
Aviation meteorology- one of the branches of military meteorology that studies meteorological elements and atmospheric phenomena from the point of view of their influence on aviation equipment and combat activities military air force, as well as developing and... Brief dictionary operational-tactical and general military terms
Aviation science and technology In pre-revolutionary Russia, a number of aircraft of original design were built. Y. M. Gakkel, D. P. Grigorovich, V. A. Slesarev and others created their own aircraft (1909 1914). 4 motor aircraft were built... ... Great Soviet Encyclopedia
