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 a gaseous state it is lighter than air. The weight of water vapor is 5/8 of the weight of dry air. As a result, moist air rises above dry air.

Atmospheric movement

Wind.

Wind arises from a pressure imbalance, usually in 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 force, it is an 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 the increased pressure in front of them. In this case, the frontal boundary is called a stationary front.

Rice. 33 cold front warm front

Front of occlusion.

Clouds

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 the tops of mountains during strong winds. 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 air layer 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 sunny days heated by the earth's surface. The lifting speed reaches 15 m/s, but usually it is 1-5 m/s.

Dew point and cloud height.

The saturation temperature is called the dew point. 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 occurs 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.

HORIZONTAL VISIBILITY RANGE AND ITS DEPENDENCE ON VARIOUS FACTORS

Visibility- this is the visual perception of objects, due to the existence of brightness and color differences between objects and the background on which they are projected. Visibility is one of the most important meteorological factors affecting flight operations and especially the takeoff and landing of aircraft, since about 80% necessary information the pilot receives it visually. Visibility is characterized by the range of visibility (how far one can see) and the degree of visibility (how well one can see). When providing meteorological support to aviation, only visual range is used, which is usually called visibility.

Distance visible awns- this is the maximum distance from which unlit objects during the day and illuminated landmarks at night are visible and identified. It is assumed that the object is always accessible to the observer, i.e. The terrain and the spherical shape of the Earth do not limit the possibility of observation. Visibility is assessed quantitatively through distance and depends on the geometric dimensions of the object, its illumination, the contrast of the object and the background, and the transparency of the atmosphere.

Geometric dimensions of the object. The human eye has a certain resolution and can see objects whose dimensions are at least one arcminutes. In order for an object not to turn into a point at a distance, but to be able to be identified, its angular size must be at least 15¢. Therefore, the linear dimensions of objects on the earth's surface selected for visual determination of visibility should increase with distance from the observer. Calculations show that to confidently determine visibility, an object must have linear dimensions of at least 2.9 m (at a distance of 500 m), 5.8 m (at a distance of 1000 m) and 11.6 m (at a distance of 2000 m). m). The shape of an object also affects visibility. Objects with sharply defined edges (buildings, masts, pipes, etc.) are visible better than objects with blurry edges (forest, etc.).

Illumination. To observe an object, it must be illuminated.

The human eye remains resistant to the perception of objects in bright light

20…20000 lux (lux). Daylight illumination varies within 400...100000 lux.

If the illumination of an object is less than the limit for the eye, then the object becomes invisible.

The contrast of the object with the background. An object of sufficient angular dimensions can be seen only if it differs in brightness or color from the background on which it is projected. Brightness contrast is of decisive importance, since the color contrast of distant objects is smoothed out due to optical haze.

Optical haze- this is a kind of light curtain, which is formed as a result of the scattering of light rays by liquid and solid particles in the atmosphere (products of condensation and sublimation of water vapor, dust, smoke, etc.). Objects viewed from a distance through optical haze will usually change color, their colors will fade, and they will appear to have a grayish-blue tint.

Luminance contrast K- this is the ratio of the absolute difference in brightness of an object In and background Vf to most of them.

Bo>Bf

(condition for observing luminous objects at night), then:

K=B o - B f

If Bf>Bo

(condition for observing dark objects during the day), then:

K=B f - B about

The brightness contrast varies within the range of 0…1. At

Bo=Bf,

the object is not

visible At Bo= 0 , TO

1 object is a black body.

Contrast sensitivity threshold e is the lowest value of brightness contrast at which the eye stops seeing the object. The value of e is not constant. It varies from person to person and depends on the illumination of the object and the degree of adaptation of the observer’s eye to this illumination. Under conditions of normal daylight and sufficient angular dimensions, the object a can be detected at e = 0.05. The loss of its visibility occurs at e = 0.02. In aviation, the accepted value is e = 0.05. If the illumination decreases, then the contrast sensitivity of the eye increases. At dusk and at night

e = 0.6…0.7. Therefore, the brightness of the background in these cases should be 60...70% greater than the brightness of the object.

Transparency of the atmosphere- this is the main factor determining the range of visibility, since the observed contrasts between the brightness of the object and the background depend on the optical properties of the air, on the attenuation and scattering of light rays in it. The gases that make up the atmosphere are extremely transparent. If the atmosphere consisted only of pure gases, then the visibility range in daylight would reach approximately 250...300 km. Water droplets, ice crystals, dust and smoke particles suspended in the atmosphere scatter light rays. As a result, an optical haze is formed, which deteriorates the visibility of objects and lights in the atmosphere. The more suspended particles in the air, the greater the brightness of the optical haze and the more distant objects are visible. The transparency of the atmosphere is worsened by the following weather phenomena: all types of precipitation, haze, fog, haze, dust storm, drifting snow, blowing snow, general snowstorm.

The transparency of the atmosphere x is characterized by the transparency coefficient t. It shows how much the light flux passing through a 1 km thick layer of the atmosphere is weakened by various impurities deposited in this layer.

TYPES OF VISIBILITY

Meteorological visual range (MVR)- this is the maximum distance at which black objects with angular dimensions of more than 15¢, projected against the sky near the horizon or against the background of haze, are visible and identified during daylight hours.

In instrumental observations, visibility is taken to be m meteorological optical visibility range (MOR - meteorological optical range), which is understood as the length of the path of the light flux in the atmosphere, at which it weakens to 0.05 from its initial value.

The MOR depends only on transparency and the atmosphere, is included in information about the actual weather at the aerodrome, is plotted on weather maps and is a primary element in assessing visibility conditions and for aviation needs.

Visibility for aviation purposes– is the greater of the following quantities:

a) the maximum distance at which a black object of appropriate size, located near the ground and observed against a light background, can be distinguished and identified;

b) the maximum distance at which lights with a light intensity of about 1000 candelas can be distinguished and identified against an illuminated background.

These distances have different meanings in air with a given attenuation coefficient.

Prevailing Visibility is the highest value of visibility observed in accordance with the definition of the term visibility which is achieved within at least half the horizon line or within at least half the surface of the aerodrome. The surveyed space can include adjacent and non-adjacent sectors.

Runway visual range Runway visual range (RVR) is the distance within which the pilot of an aircraft located on the runway center line can see the runway pavement markings or lights that limit the runway or indicate its center line. The height of the average eye level of the pilot in the aircraft cockpit is assumed to be 5 m. RVR measurements by an observer are practically impossible, its assessment is carried out by calculations based on Koschmider's law (when using objects or markers) and Allard's law (when using lights). The RVR value included in the reports is the greater of these two values. RVR calculations are carried out only at aerodromes equipped with high-intensity (HI) or low-intensity (LMI) lighting systems, with maximum visibility along the runway less than

1500 m. For visibility greater than 1500 m, visibility RVR is identified with MOR. Guidance regarding the calculation of visibility and RVR is contained in the Manual of Runway Visual Range Observing and Reporting Practices (DOS 9328).

Vertical visibility- this is the maximum height from which a crew in flight sees the ground vertically down. In the presence of clouds, vertical visibility is equal to the height of the lower boundary of the clouds or less than it (in fog, in heavy precipitation, in general blowing snow). Vertical visibility is determined using instruments that measure heights at the bottom of the clouds. Vertical visibility information is included in aerodrome actual weather reports instead of cloud base height.

Oblique visibility- this is the maximum distance along the descent glide path at which the pilot of an aircraft approaching to land, when transitioning from instrument to visual piloting, can detect and identify the beginning of the runway. In difficult meteorological conditions (visibility 2000 m or less and/or cloud base height 200 m or less), oblique visibility may be significantly less than horizontal visibility at the ground surface. This happens when there are retaining layers (inversion, isotherm) between the flying aircraft and the earth’s surface, under which small droplets of water, dust particles, industrial atmospheric pollution, etc. accumulate; or when an aircraft is landing in low clouds (below 200 m), under which there is a subcloud layer of thick haze of variable optical density.

Oblique visibility is not determined instrumentally. It is calculated based on the measured MOR. On average, with a cloud base height of less than 200 m and MOR less than 2000 m, slant visibility is 50% of the horizontal range and runway visibility.

Very weather dependent: snow, rain, fog, low clouds, strong gusty winds and even complete calm - unfavourable conditions for the jump. Therefore, athletes often have to sit on the ground for hours and weeks, waiting for a “window of good weather.”

Signs of persistent good weather

1. High blood pressure that rises slowly and continuously over several days.
2. Correct daily wind pattern: quiet at night, significant wind strength during the day; on the shores of seas and large lakes, as well as in the mountains, the correct change of winds is:
   • during the day - from water to land and from valleys to peaks,
   • at night - from land to water and from peaks to valleys.
3. In winter the sky is clear, and only in the evening when it is calm can thin stratus clouds appear. In summer, on the contrary: cumulus clouds develop and disappear in the evening.
4. Correct daily temperature variation (increase during the day, decrease at night). In winter the temperature is low, in summer it is high.
5. There is no precipitation; heavy dew or frost at night.
6. Ground fogs that disappear after sunrise.

Signs of persistent bad weather

1. Low pressure, changing little or decreasing even more.
2. Lack of normal daily wind patterns; wind speed is significant.
3. The sky is completely covered with nimbostratus or stratus clouds.
4. Prolonged rain or snowfall.
5. Minor temperature changes during the day; relatively warm in winter, cool in summer.

Signs of worsening weather

1. Pressure drop; The faster the pressure drops, the sooner the weather will change.
2. The wind intensifies, its daily fluctuations almost disappear, and the wind direction changes.
3. Cloudiness increases, and the following order of appearance of clouds is often observed: cirrus appears, then cirrostratus (their movement is so fast that it is noticeable to the eye), cirrostratus is replaced by altostratus, and the latter by nimbostratus.
4. Cumulus clouds do not dissipate or disappear in the evening, and their number even increases. If they take the form of towers, then a thunderstorm should be expected.
5. The temperature rises in winter, but in summer there is a noticeable decrease in its diurnal variation.
6. Colored circles and crowns appear around the Moon and Sun.

Signs of improving weather

1. The pressure rises.
2. Cloud cover becomes variable and breaks appear, although at times the entire sky may still be covered with low rain clouds.
3. Rain or snow falls from time to time and is quite heavy, but it does not fall continuously.
4. The temperature drops in winter and rises in summer (after a preliminary decrease).

“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...”

-- [ Page 1 ] --

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

–  –  –

INTRODUCTION

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. Meteorological flight conditions are considered and given practical recommendations on the most appropriate actions of flight personnel 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, westerly winds predominate, and clouds and precipitation form.

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 satellites Lands equipped with special equipment.

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 Movement aircraft in the atmosphere is accompanied by a 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;

The average sea level at which the air pressure is 760 mm Hg is taken as zero altitude (“ground”). Art. or 1013.25 hPa.

Temperature +15°C

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.

Zero on this scale corresponds to complete cessation thermal movement 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 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. So raising her up high altitudes 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 make operation difficult aviation technology. 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 1 m3 of air. The higher the air temperature, the greater the 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 relative humidity 20-40% air is considered dry, 80-100% is considered humid, and 50-70% is 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. Magnitude atmospheric pressure measured in mmHg.

millibars and hectopascals. There is a dependency between them:

–  –  –

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 the 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 the average speed in case of a difference of 3 m/s if the wind is cross (at each airport their gradations), and in other cases after 5m/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 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) towards the warm sea. Observed in autumn-winter period, accompanied by a sharp drop in temperature, is expressed in the region of Novorossiysk, in a northeastern direction. Bora occurs in the presence of an anticyclone formed and located over the eastern and south-eastern regions of the European territory of Russia, and at this time there is an area of ​​low pressure over the Black Sea, while large pressure gradients are created and cold air rushes through the Markhotsky pass from a height of 435 m to 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 are playing vital role in such atmospheric processes as vertical transfer of heat and water vapor, formation of clouds and precipitation, cloud dispersion, development of thunderstorms, occurrence 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 (transition of water vapor into a liquid state) and sublimation (transition of water vapor directly into a solid state) of water vapor.

The main reason for the formation of clouds is an adiabatic (without exchange of heat with the environment) decrease in temperature in rising moist 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 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 upper limit-300-800 m. They dramatically complicate takeoff and landing 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. Above forest areas cloudiness is always lower. Over industrial centers, where there are many condensation nuclei, the frequency of cloudiness increases. The lower edge of low clouds of stratus, 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 sufficiently black object can be distinguished against the sky near the horizon large sizes. 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 air in the troposphere, which 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. Most favorable time To acquire stability, the airwave over the continent is night during the day, and winter during the year.

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 great importance has an analysis of the position of atmospheric fronts relative to the flight route and their movement.

Before departure, it is necessary to assess the activity of the front according to the following 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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4. Local weather signs

6. Aviation weather forecast

1. Atmospheric phenomena dangerous to aviation

Atmospheric phenomena are important element weather: whether it is raining or snowing, whether there is fog or a dust storm, whether a blizzard or thunderstorm is raging, largely depends on how one perceives current state atmosphere by living beings (humans, animals, plants), and the impact of weather on open-air machines and mechanisms, buildings, roads, etc. Therefore, observations of atmospheric phenomena (their correct definition, recording start and stop times, intensity fluctuations) on a network of weather stations are of great importance. Big influence atmospheric phenomena have an impact on the activities of civil aviation.

Regular weather conditions on Earth these are wind, clouds, precipitation (rain, snow, etc.), fog, thunderstorms, dust storms and blizzards. Rarer events include natural disasters such as tornadoes and hurricanes. The main consumers of meteorological information are navy and aviation.

Atmospheric phenomena dangerous to aviation include thunderstorms, squalls (wind gusts of 12 m/sec and above, storms, hurricanes), fog, icing, rainfall, hail, blizzards, dust storms, low clouds.

A thunderstorm is a phenomenon of cloud formation accompanied by electrical discharges in the form of lightning and precipitation (sometimes hail). The main process in the formation of thunderstorms is the development of cumulonimbus clouds. The base of the clouds reaches an average height of 500 m, and the upper limit can reach 7000 m or more. Strong vortex air movements are observed in thunderclouds; In the middle part of the clouds, pellets, snow, and hail are observed, and in the upper part there is a blizzard. Thunderstorms are usually accompanied by squalls. There are intramass and frontal thunderstorms. Frontal thunderstorms develop mainly on cold atmospheric fronts, less often on warm ones; the band of these thunderstorms is usually narrow in width, but along the front it covers an area of ​​up to 1000 km; observed day and night. Thunderstorms are dangerous due to electrical discharges and strong vibrations; A lightning strike on an airplane can lead to serious consequences. During a severe thunderstorm, radio communications should not be used. Flights in the presence of thunderstorms are extremely difficult. Cumulonimbus clouds must be avoided from the side. Less vertically developed thunderclouds can be overcome from above, but at a significant elevation. In exceptional cases, the intersection of thunderstorm zones can be accomplished through small cloud breaks found in these zones.

A squall is a sudden increase in wind with a change in its direction. Squalls usually occur during the passage of pronounced cold fronts. The width of the squall zone is 200-7000 m, the height is up to 2-3 km, and the length along the front is hundreds of kilometers. Wind speed during squalls can reach 30-40 m/sec.

Fog is a phenomenon of condensation of water vapor in the ground layer of air, in which the visibility range is reduced to 1 km or less. With a visibility range of more than 1 km, condensation haze is called haze. According to the conditions of formation, fogs are divided into frontal and intramass. Frontal fogs are more common during the passage of warm fronts, and they are very dense. Intramass fogs are divided into radiation (local) and adventive (moving cooling fogs).

Icing is the phenomenon of ice deposits on various parts of an aircraft. The cause of icing is the presence of water droplets in the atmosphere in a supercooled state, that is, with temperatures below 0° C. The collision of droplets with an airplane leads to their freezing. Ice buildup increases the weight of the aircraft, reduces its lift, increases drag, etc.

There are three types of icing:

b deposition of pure ice (the most dangerous type of icing) is observed when flying in clouds, precipitation and fog at temperatures from 0° to -10° C and below; deposition occurs primarily on the frontal parts of the aircraft, cables, tail surfaces, and in the nozzle; ice on the ground is a sign of the presence of significant icing zones in the air;

b frost - a whitish, granular coating - a less dangerous type of icing, it occurs at temperatures up to -15--20 ° C and below, settles more evenly on the surface of the aircraft and does not always hold tightly; a long flight in an area that produces frost is dangerous;

ь frost is observed at fairly low temperatures and does not reach dangerous sizes.

If icing begins while flying in the clouds, you must:

b if there are breaks in the clouds, fly through these gaps or between layers of clouds;

b if possible, go to an area with a temperature above 0°;

b if it is known that the temperature near the ground is below 0° and the height of the clouds is insignificant, then it is necessary to gain altitude in order to get out of the clouds or get into a layer with lower temperatures.

If icing began while flying in freezing rain, you must:

b fly into a layer of air with a temperature above 0°, if the location of such a layer is known in advance;

b leave the rain zone, and if the icing is threatening, return or land at the nearest airfield.

A blizzard is a phenomenon of snow being transported by the wind in a horizontal direction, often accompanied by vortex movements. Visibility in snowstorms can decrease sharply (to 50-100 m or less). Blizzards are typical for cyclones, the periphery of anticyclones and fronts. They make it difficult for an airplane to land and take off, sometimes making it impossible.

Mountainous areas are characterized by sudden changes in weather, frequent cloud formations, precipitation, thunderstorms, and changing winds. In the mountains, especially in the warm season, there is constant upward and downward movement of air, and air vortices arise near the mountain slopes. The mountain ranges are mostly covered with clouds. During the day and in summer these are cumulus clouds, and at night and in winter they are low stratus clouds. Clouds form primarily over the tops of mountains and on their windward side. Cumulus clouds over mountains are often accompanied by heavy downpours and thunderstorms with hail. Flying near mountain slopes is dangerous, as the plane may get caught in air vortices. The flight over the mountains must be carried out at an altitude of 500-800 m; the descent after flying over the mountains (peaks) can begin at a distance of 10-20 km from the mountains (peaks). Flying under clouds can be relatively safe only if the lower boundary of the clouds is located at an altitude of 600-800 m above the mountains. If this limit is lower than the specified altitude and if the mountain tops are closed in places, then the flight becomes more difficult, and with further decrease in clouds it becomes dangerous. In mountainous conditions, breaking through the clouds upward or flying through the clouds using instruments is possible only with excellent knowledge of the flight area.

2. Effect of clouds and precipitation on flight

aviation weather atmospheric

The influence of clouds on flight.

The nature of the flight is often determined by the presence of clouds, its height, structure and extent. Cloudiness complicates piloting technique and tactical actions. Flight in the clouds is difficult, and its success depends on the availability of appropriate flight and navigation equipment on the aircraft and on the training of the flight crew in instrument piloting techniques. In powerful cumulus clouds, flying (especially on heavy aircraft) is complicated by high air turbulence; in cumulonimbus clouds, in addition, the presence of thunderstorms.

In the cold season, and at high altitudes and in the summer, when flying in the clouds there is a danger of icing.

Table 1. Cloud visibility value.

Effect of precipitation on flight.

The influence of precipitation on flight is mainly due to the phenomena accompanying it. Covering precipitation (especially drizzle) often covers large areas, is accompanied by low clouds and greatly impairs visibility; If there are supercooled droplets in them, icing of the aircraft occurs. Therefore, in heavy precipitation, especially at low altitudes, flight is difficult. In frontal rainfall, flight is difficult due to a sharp deterioration in visibility and increased wind.

3. Responsibilities of the aircraft crew

Before departure, the aircraft crew (pilot, navigator) must:

1. Hear a detailed report from the meteorologist on duty about the condition and weather forecast along the flight route (area). In this case, special attention should be paid to the presence along the flight route (area):

b atmospheric fronts, their position and intensity, vertical power of frontal cloud systems, direction and speed of movement of fronts;

b zones with hazardous weather phenomena for aviation, their boundaries, direction and speed of displacement;

b ways to avoid areas with bad weather.

2. Receive a weather bulletin from the weather station, which should indicate:

b actual weather along the route and at the landing point no more than two hours ago;

b weather forecast along the route (area) and at the landing point;

b vertical section of the expected state of the atmosphere along the route;

b astronomical data of departure and landing points.

3. If the departure is delayed by more than an hour, the crew must listen again to the report of the duty meteorologist and receive a new weather bulletin.

During the flight, the aircraft crew (pilot, navigator) is obliged to:

1. Observe weather conditions, especially phenomena dangerous to flight. This will allow the crew to promptly notice a sharp deterioration in weather along the flight route (area), correctly assess it, make an appropriate decision for the further flight and complete the task.

2. Request 50-100 km before approaching the airfield information about the meteorological situation in the landing area, as well as barometric pressure data at the airfield level and set the resulting barometric pressure value on the on-board altimeter.

4. Local weather signs

Signs of persistent good weather.

1. High blood pressure, slowly and continuously increasing over several days.

2. Correct daily wind pattern: quiet at night, significant wind strength during the day; on the shores of seas and large lakes, as well as in the mountains, there is a regular change of winds: during the day - from water to land and from valleys to peaks, at night - from land to water and from peaks to valleys.

3. In winter, the sky is clear, and only in the evening when it is calm, thin stratus clouds can float. In summer, it’s the opposite: cumulus clouds develop during the day and disappear in the evening.

4. Correct daily temperature variation (increase during the day, decrease at night). In the winter half of the year the temperature is low, in the summer it is high.

5. No precipitation; heavy dew or frost at night.

6. Ground fogs that disappear after sunrise.

Signs of persistent bad weather.

1. Low pressure, changing little or decreasing even more.

2. Lack of normal daily wind patterns; wind speed is significant.

3. The sky is completely covered with nimbostratus or stratus clouds.

4. Prolonged rain or snowfall.

5. Minor changes in temperature during the day; relatively warm in winter, cool in summer.

Signs of worsening weather.

1. Pressure drop; The faster the pressure drops, the sooner the weather will change.

2. The wind intensifies, its daily fluctuations almost disappear, and the wind direction changes.

3. Cloudiness increases, and the following order of appearance of clouds is often observed: cirrus appears, then cirrostratus (their movement is so fast that it is noticeable to the eye), cirrostratus is replaced by altostratus, and the latter by cirrostratus.

4. Cumulus clouds do not dissipate or disappear in the evening, and their number even increases. If they take the form of towers, then a thunderstorm should be expected.

5. The temperature rises in winter, but in summer there is a noticeable decrease in its diurnal variation.

6. Colored circles and crowns appear around the Moon and Sun.

Signs of improving weather.

1. Pressure rises.

2. Cloud cover becomes variable and breaks appear, although at times the entire sky may still be covered with low rain clouds.

3. Rain or snow falls from time to time and is quite heavy, but it does not fall continuously.

4. The temperature decreases in winter and increases in summer (after a preliminary decrease).

5. Examples of plane crashes due to atmospheric phenomena

On Friday, a Uruguayan Air Force FH-227 turboprop carried the Old Christians junior rugby team from Montevideo, Uruguay, across the Andes for a match in the Chilean capital of Santiago.

The flight began the day before, on October 12, when the flight took off from Carrasco Airport, but due to bad weather, the plane landed at the airport in Mendoza, Argentina and remained there overnight. The plane was unable to fly directly to Santiago due to weather, so the pilots had to fly south parallel to the Mendoza Mountains, then turn west, then head north and begin their descent to Santiago after passing through Curico.

When the pilot reported passing Curico, the air traffic controller cleared the descent to Santiago. This was a fatal mistake. The plane flew into a cyclone and began to descend, guided only by time. When the cyclone was passed, it became clear that they were flying straight onto the rock and there was no way to avoid the collision. As a result, the plane caught the top of the peak with its tail. Due to impacts with rocks and the ground, the car lost its tail and wings. The fuselage rolled at great speed down the slope until it crashed nose-first into blocks of snow.

More than a quarter of the passengers died when they fell and collided with a rock, and several more died later from wounds and cold. Then, of the remaining 29 survivors, 8 more died in an avalanche.

The crashed plane belonged to the special transport aviation regiment of the Polish Army, which served the government. The Tu-154-M was assembled in the early 1990s. The plane of the President of Poland and the second similar government Tu-154 from Warsaw underwent scheduled repairs in Russia, in Samara.

Information about the tragedy that took place this morning on the outskirts of Smolensk still has to be collected bit by bit. The Polish President's Tu-154 plane was landing near the Severny airfield. This is a first-class runway and there were no complaints about it, but at that hour the military airfield was not accepting planes due to bad weather. The hydrometeorological center of Russia predicted heavy fog the day before, visibility 200 - 500 meters, these are very bad conditions for landing, on the verge of a minimum even for the best airports. Some ten minutes before the tragedy, dispatchers deployed a Russian transporter to a reserve site.

None of those on board the Tu-154 survived.

The plane crash occurred in northeast China - according to various estimates, about 50 people survived and more than 40 died. The Henan Airlines plane, flying from Harbin, overshot the runway in heavy fog when landing in the city of Yichun, broke into pieces on impact and caught fire.

There were 91 passengers and five crew members on board. The victims were taken to the hospital with fractures and burns. The majority are in a relatively stable condition, their lives are not in danger. Three are in critical condition.

6. Aviation weather forecast

In order to avoid aircraft crashes due to atmospheric phenomena, aviation weather forecasts are developed.

The development of aviation weather forecasts is a complex and interesting branch of synoptic meteorology, and the responsibility and complexity of such work is much higher than when preparing conventional forecasts for general use (for the population).

The source texts of airport weather forecasts (code form TAF - Terminal Aerodrome Forecast) are published as they are compiled by the weather services of the corresponding airports and transmitted to the worldwide weather information exchange network. It is in this form that they are used for consultations with airport flight control personnel. These forecasts are the basis for analyzing the expected weather conditions at the landing point and making a decision on departure by the crew commander.

The weather forecast for the airfield is compiled every 3 hours for a period from 9 to 24 hours. As a rule, forecasts are issued at least 1 hour 15 minutes before the start of their validity period. In case of sudden, previously unpredicted weather changes, an extraordinary forecast (adjustment) may be issued; its lead time may be 35 minutes before the start of the validity period, and the validity period may differ from the standard one.

Time in aviation forecasts is indicated in Greenwich Mean Time (Universal Time - UTC), to obtain Moscow time you must add 3 hours to it (during summer time - 4 hours). The name of the airfield is followed by the day and time of the forecast (for example, 241145Z - on the 24th at 11:45), then the day and period of validity of the forecast (for example, 241322 - on the 24th from 13 to 22 hours; or 241212 - on the 24th from 12 o'clock to 12 o'clock the next day; for extraordinary forecasts, minutes can also be indicated, for example 24134022 - on the 24th from 13-40 to 22 o'clock).

The weather forecast for an aerodrome includes the following elements (in order):

b wind - direction (from where it blows, in degrees, for example: 360 - north, 90 - east, 180 - south, 270 - west, etc.) and speed;

b horizontal visibility range (usually in meters, in the USA and some other countries - in miles - SM);

b weather phenomena;

b cloudiness by layers - amount (clear - 0% of the sky, isolated - 10-30%, scattered - 40-50%, significant - 60-90%; continuous - 100%) and the height of the lower boundary; in case of fog, snowstorm and other phenomena, vertical visibility may be indicated instead of the lower limit of clouds;

b air temperature (indicated only in some cases);

b presence of turbulence and icing.

Note:

Responsibility for the accuracy and accuracy of the forecast lies with the weather forecasting engineer who developed this forecast. In the West, when compiling airfield forecasts, data from global computer modeling of the atmosphere are widely used; the weather forecaster only makes minor clarifications to these data. In Russia and the CIS, airfield forecasts are developed mainly manually, using labor-intensive methods (analysis of synoptic maps, taking into account local aeroclimatic conditions), and therefore the accuracy and accuracy of forecasts is lower than in the West (especially in complex, sharply changing synoptic conditions).

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