Methods for determining average wind. The concept of average wind. Determination of wind direction and speed.

Wind is the movement of air that occurs parallel earth's surface and is horizontal in nature. The main property of such a flow is its velocity vector. In practice, this value represents numeric value. Additional characteristics are the direction and strength of the wind. There are several classifications based on these criteria.

General concepts

Wind on planet Earth is a flow of air that predominantly moves horizontally. A similar phenomenon is observed in other cosmic bodies. However, in this case we are already talking about the flow of atmospheric gases. This is how solar and planetary winds are distinguished.

Air flows on Earth are classified by speed, scale, strength, impact on objects and areas of distribution. Nevertheless, main characteristic the wind direction still remains. Also, we should not forget about its duration. It is by these criteria that winds are classified in the first place. For example, short-term and long-term, strong and weak, etc. Powerful short-term flows are called squalls. Their duration rarely exceeds 1 minute. The longest lasting ones include breeze, storm, storm, typhoon and hurricane. All of them are additionally characterized by the forces of origin and impact. In turn, the duration of the wind can be from a couple of seconds to several months. This phenomenon depends on the difference in heating of air particles, relief features, and atmospheric circulation.

In rare cases, vertical winds occur. Their movement is directed from bottom to top or vice versa. Such flows are called downward or upward.

Methods for measuring characteristics

To find out what direction the wind is, you need to use one of the special devices. Each of these instruments shows the azimuth of the stream's origin point. The resulting values ​​will be in the range of 180 degrees.

Wind speed and direction can be measured with an anemometer. This device has found application in the energy industry. The flow hits a special membrane. The push is detected by a sensor, the data is processed and displayed on the screen.

To measure purely the direction of the wind, you can use a regular weather vane. This tool works even with the slightest breeze. As a result, the arrow will indicate the direction of the wind. The error depends on the quality of the weather vane. On average, it varies between 2-3%.

If you don't have the necessary tools at hand, you can use index finger. Just wet it and put it up. Your finger will quickly feel cool. Thus, it is possible to determine from which side the flow is moving. On the other hand, this technology does not work in hot, humid climates.

Direction of the wind

The movement of the air flow is determined horizontally along the side from which it originates. If it blows north, then the wind direction is south. Such movement directly depends on the force of rotation of the planet and the distribution atmospheric pressure. The closer the flows are to the Earth's surface, the more variable they are.

As you know, water and land heat up with at different speeds. IN summer time The temperature of the earth's surface is rising rapidly. As a result of this phenomenon, the air heats up, expands and becomes much lighter. In turn, it is always colder above the surface of the water. Consequently, air flows become heavier and more compressed. Therefore, it is from the direction of the water that the cool wind always blows. At night, flows often come from the shore.

Another place where winds arise can be mountainous areas. In this case, a dry and warm flow is called a “fen”, and a strong and cold flow is called “bora”.

Classification by wind speed

This characteristic is measured in points or meters per second. Depends on the so-called pressure gradient. The smaller its value, the lower the flow rate. For reference: 1 point is approximately equal to 2 m/s.

It is true that the strength of the wind directly depends on its speed. In addition, the greater the pressure difference between the involved surface areas, the more powerful the flow will be. Today there is a Beaufort scale, which determines the strength of the wind:

The most powerful winds

Several years ago, the Beaufort scale was expanded by the American National Weather Service. Additions apply only to the “hurricane” category:

12.1 points - strong windfall. Its speed ranges from 35 to 42 m/s. At the same time, the wind changes direction constantly. The destructive impact extends to telegraph poles and wooden buildings.

- 12.2 points. Such a hurricane has a speed of up to 49 m/s. There was damage to the roofs, doors and windows of stone buildings.

12.3 points. Wind at a speed of up to 58 m/s destroys the lungs of houses, causing waves with a height of up to 3.5 m. Flooding is possible.

12.4 points. Such a windfall is characterized by a movement speed of 59-70 m/s. The stream uproots medium-sized trees and causes severe damage to strong buildings.

12.5 points. Wind speeds exceeding 71 m/s destroy powerful buildings, including stone ones. Deep craters remain in the ground. Heavy objects rise into the sky. Flooding is inevitable.

Local winds

Most often, such flows form on the plains of the continent or over the sea. One of the most common types is breeze. In this case, the prevailing wind direction is characterized by local circulation of warm air. Formed due to the difference low pressure at positive temperatures.

Local wind speeds rarely exceed 4 m/s. More intense flows come from mountain ranges. Formation occurs at heights, and blowing occurs primarily in valleys.

Global winds

We are talking about monsoons and trade winds. The first type of global winds is seasonal. It changes its direction only 2 times a year. Tropical monsoons move from mid-latitudes. They are mostly warm. Extratropical winds blow from polar and temperate latitudes, significantly reducing air temperatures.

Trade winds depend on atmospheric pressure. Most often they blow from the west. On rare occasions, easterly and southerly trade winds can be observed. The main location of distribution is the equator zone.

1. Wind speed and direction.

2. Forces acting on the wind. Theoretical types of wind.

3. Wind conditions in the Republic of Belarus.

1. Wind speed and direction

Wind – horizontal movement air relative to the earth's surface.

Movements of various scales are observed in the atmosphere - from tens to hundreds of meters (local winds) to hundreds and thousands of kilometers (cyclones, anticyclones, trade winds, monsoons). Air currents are directed from areas of high pressure towards low pressure. The outflow of air continues until the pressure difference disappears.

1.1. Wind speed

Wind is characterized by a speed vector. Wind speed can be measured in different units: meters per second (m/s), kilometers per hour (km/h), knots (nautical miles per hour), points. There are smoothed wind speeds (over a certain period of time) and instantaneous ones.

Ground speed average speed wind speed is usually 5–10 m/s and rarely exceeds 12–15 m/s. In tropical hurricanes it reaches up to 60–65 m/s, in gusts – up to 100 m/s; in tornadoes and blood clots – 100 m/s or more. The maximum measured speed is 87 m/s (Adelie Terre, Antarctica).

Wind speed at most weather stations is measured by rotating cup anemometers, invented in 1846. In addition to cup or vane anemometers, wind speed can be estimated using a Wild board. One of the first anemometers was invented in 1450 by the Italian Leon Alberti. It was a lever anemometer: the wind pushed a ball or plate in the device, moving it along a curved scale with divisions. The stronger the wind, the more the ball shifted. Instruments for measuring wind speed are installed at a height of 10–12 m.

1.2. Direction of the wind

Direction of the wind in meteorology, the direction from which it blows. It can be indicated by naming the point on the horizon from which the wind blows (i.e., the direction) or the angle that the horizontal wind speed vector makes with the meridian (i.e., the azimuth).

The direction of the wind in high layers of the atmosphere is indicated in degrees, and in surface layers - in horizon points (Figure 54). During observations, the wind direction is determined by 16 points, but during processing, the observation results are usually reduced to 8 points.

Figure 54 – Horizon points

Main directions (8): north, northeast, east, southeast, south, southwest, west, northwest. Intermediate directions (8): north-northeast, east-northeast, east-southeast, south-southeast, south-southwest, west-southwest, north-northwest.

International names of directions: north – N – north; east – E – east; south – S – south; west – W – west.

In some places, the winds are named after the direction from which they blow. Example: Russian wind – wind from the central regions European Russia, in the north of European Russia it is a south wind, in Siberia it is a westerly wind, in Romania it is a northeast wind. In the Caspian region, the northern wind is called Ivan, and the southern wind is called Mohammed.

The wind direction is determined using weather vane 1 (from hol. vleugel– wing) – one of the oldest meteorological instruments. The weather vane consists of a weather vane and a cross of rhumbs. A Wild weather vane 2 is often installed at weather stations. It consists of a metal flag rotating around a vertical axis above a cross of rhumbs, and a Wild board. Anemographs use a Saleiron wheel - 2 mills mounted on a movable axis, and an arrow indicating the direction of the wind.

As with speed, a distinction is made between instantaneous and smoothed wind direction. Instantaneous wind directions fluctuate significantly around a certain average (smoothed) direction, which is determined by observations from a weather vane. However, the smoothed direction of the wind in each place on Earth is constantly changing, and in different places at the same time it is also different. In some places, winds of different directions have almost equal frequency over a long period of time, in others there is a well-defined predominance of some wind directions over others throughout the entire season or year. This depends on the conditions of the general circulation of the atmosphere and partly on local topographic conditions.

When climatologically processing wind observations, it is possible to construct for each given point a diagram representing the distribution of the frequency of wind directions along the main directions, in the form of a so-called wind rose (Figure 55).

Figure 55 – Frequency of wind direction in Brest, % (wind rose)

From start polar coordinates directions are plotted along the horizon points (8 or 16) in segments, the lengths of which are proportional to the frequency of winds in a given direction. The ends of the segments can be connected by a broken line. The frequency of calms is indicated by the number in the center of the diagram (at the origin). If we plot segments proportional to the average wind speed from the center of the diagram, we get a rose of average wind speeds. When constructing a wind rose, you can take into account 2 parameters simultaneously (by multiplying the frequency of wind directions and the average wind speed in each direction). Such a diagram will reflect the amount of air carried by winds of different directions.

For presentation on climate maps, wind direction is generalized in different ways:

compass roses can be plotted on the map in different places;

it is possible to determine the resultant of all wind speeds (considered as vectors) in this place for one or another calendar month over a multi-year period and then take the direction of this resultant as the average wind direction;

indicate the prevailing wind direction. To do this, the square with the greatest repeatability is determined, middle line the square is the predominant direction.

Wind usually refers to the longitudinal directional movement of atmospheric flows. This natural phenomenon is observed on all planets where there is an atmosphere, and the direction of atmospheric flows can be unpredictable. On Earth, the atmosphere is relatively calm, so it is customary to separate ordinary winds that blow longitudinally along the surface from phenomena such as tornadoes or vertical flows.

According to modern meteorological standards, all terrestrial objects are divided depending on the following parameters:

• scale and area of ​​distribution;
• strength and speed;
• nature of occurrence;
• duration;

Formation of atmospheric flows, their scale

First important characteristic— scale and associated area of ​​distribution (influence) of winds. There are global atmospheric currents: monsoons, trade winds, easterly and westerly winds, polar and subtropical atmospheric fronts. They belong to the so-called constant winds of the planet and are formed as a result of large-scale climate shifts when the seasons change.

Local winds are formed against the background of local climatic features— with temperature changes, along reservoirs or mountain ranges. The most famous local winds are boron, foehn, breeze, dry winds and many other atmospheric currents characteristic of a particular area. Their occurrence is determined by both interseasonal changes in air flows and various geographical features.

Duration is another parameter characterizing Various types winds. Long-term winds with a wide coverage area were considered above, but there are also short-term limited atmospheric disturbances. These include various local anticyclones and cyclones, thunderstorms, tornadoes, seasonal winds and some others. This type of wind is the most common and fickle, it can form within a few days and die out just as quickly.

The influence of wind on weather conditions

Atmospheric flows are one of the fundamental natural factors, which is directly related to the majority natural phenomena. Cyclones and anticyclones, which cause local climate changes, are local atmospheric formations. They can lead to sudden changes in weather that are uncharacteristic for a certain region.

Another example of the influence of winds on weather is thunderstorms and hail. It is under the influence of hot rising winds that strong thunderstorm winds are formed and electrification occurs between water molecules. According to the latest data, all weather phenomena are influenced by atmospheric fronts: including rains, droughts, natural fires, hurricanes.

In addition, local winds produce phenomena such as turbulence and icing, which makes it important to study and timely monitor them.

Wind speed and strength, Beaufort scale

Considering the characteristics of winds, one cannot help but touch upon their strength, which is directly dependent on speed. It is measured in meters per second, and the average value within 10 minutes of continuous measurement is usually taken as the final speed. The record figure for our planet was recorded in 1996, in Australia, and was about 113-115 m/s or approximately 410 kilometers per hour. The strongest constant winds blow in Antarctica: their speed reaches 90 m/s.

Since wind speed and strength are its main potential dangerous characteristics, the international Beaufort classification scale was developed. It evaluates the approximate impact of wind speed on buildings, various ground structures, humans, nature and technology. Currently, the standard scale with 12 points has been adopted:

Please note that this table shows average speed indicators and approximate manifestations, which may differ slightly from real ones.

Wind is the horizontal component of air movement relative to the earth's surface. Occurs due to the appearance of a horizontal pressure gradient. Wind is characterized by speed (strength) and direction. Speed ​​is measured in m/sec,km'H, i’3, strength - in conventional units - points. The direction is measured in degrees of the circular division of the horizon or bearings. The direction of the wind is given a name (count) based on the point on the horizon from which the wind blows.

The wind arises under the influence of the pressure gradient force, the friction force, the deflecting force of the Earth's rotation and centrifugal force. The frictional force appears almost only up to a height of 500 m from the surface of the Earth.

If we express the wind speed V V m/sec and pressure gradient G in mb at 60 soap, That

where φ is the latitude of the place.

Pressure law of wind. If you stand with your back to the wind, then in the northern hemisphere low pressure is to the left, and high pressure is to the right of the wind direction. IN southern hemisphere vice versa.

Wind speed determined on the ship hand anemometer. With the anemometer counter turned off, count and record the arrow readings on three dials (thousands, hundreds, tens and units); stand on the windward side of the bridge, where the deckhouse fence and superstructure do not distort the wind, raise the anemometer above your head to a vertical position right hand, and on the left take the stopwatch ready for action; when the hemispheres unwind, turn on the anemometer counter and simultaneously start the stopwatch. After 100 sec, stop the anemometer counter, count a new arrow reading on all three dials of the anemometer. Subtract the initial reading from the final reading and divide the resulting difference by 100 (calculate the number of divisions in 1 sec); then in the calibration certificate find the wind speed corresponding to this number of divisions.

Direction of the wind determined at anchor or while drifting in the direction of the pennant, flag or smoke from the chimney with an accuracy of 5″. The wind is determined by the direction it is blowing from, so add 180″ to the direction of the pennant (smoke).

rcjih the speed and direction of the wind are determined as ships move, then I get!’ elements of the apparent or observed wind, which is the total vector of both the true wind and the “wind” created by the movement of the ship - the heading wind. True wind is calculated using a wind gauge (SMO circle) or graphically on a maneuverable tablet or graph paper. The procedure for determining the elements of true evening using a wind gauge is given in back side circle SMO. On a maneuverable tablet (Fig. ‘32.1, a) from the center of the tablet in the selected scale, lay reverse vector ship speed - in i/sec and apparent wind speed vector W V m/sec. Connect the end of the vector - with the end of the vector - we get the true wind vector . Vector magnitude intend

using a compass on the selected scale, determine the direction using the outer scale of the tablet, moving the vector in parallel to the center of the tablet.

Draw a line of the true meridian on graph paper (Fig. 32.1, b) and from arbitrary point On this line on the selected scale, plot the reverse vector of the ship's speed - V m/sec and apparent wind vector on the same scale. The vector will be the true wind vector; its direction will be from the end of the heading wind vector to the end of the apparent wind vector. With such constructions, we obtain the direction in which the wind is blowing, so we must add 180° to the resulting direction.

Anemorumbometer measures average true wind speed and direction.

Daily variation of the wind. The wind speed increases in the morning and weakens in the evening. In mid-latitudes this change is of the order of 3-5 m/sec. In summer, the daily variation of wind speed is greater than in winter, in clear days more than on cloudy days. Over the ocean, the daily variation of the wind is almost imperceptible.

Due to the heterogeneity of heating of different zones of the earth, there is a system of atmospheric currents on a large planetary scale ( general circulation atmosphere).

Trade winds are winds that blow all year round in one direction in the zone from the equator to 35° N. w. and up to 30° south. w. Stable in direction: in the northern hemisphere - northeast, in the southern hemisphere - southeast. Speed ​​up to 6 m/sec. Vertical power on average up to 4 km from sea level.

Monsoons are winds of temperate latitudes, blowing from the ocean to the mainland in summer and from the mainland to the ocean in winter. Reach speed 20 m/sec. Monsoons bring dry, clear and cold weather, in summer - cloudy, with rain and fog.

Breezes arise due to uneven heating of water and land during the day. At 9-10 h wind arises from sea to land (sea breeze). Night1,;o from the chilled coast ( high pressure) - on the sea (shore breeze). Wind speed in sea breezes up to 10 m/sec, for coastal - up to 5 m/sec. Breezes are observed on the shores of the Baltic, Black, Azov, Caspian and other seas. As you move further out to sea, the strength (speed) of the breeze noticeably weakens, but when favorable conditions it can be observed up to 100 miles from the shore.

Local winds arise in certain areas due to the characteristics of the relief and differ sharply from the general air flow: they arise as a result of uneven heating (cooling) of the underlying surface. Detailed information about local winds is given in sailing directions and hydrometeorological descriptions.

Bora is a strong and gusty wind directed down a mountain slope. Brings significant cooling. Observed in areas where low mountain range borders the sea, during periods when atmospheric pressure increases over land and temperature decreases compared to the pressure and temperature over the sea. In the area of ​​the Novorossiysk Bay, the bora (Novorossiysk Nord-East) operates in November - March - on average about 50 days a year - with average wind speeds of about 20 m/sec(individual gusts can be 50-60 m/sec). Duration of action is from one to three days. A sign of the presence of bora in this area is the cloud descending from the Markhot Pass. Similar winds are observed on Novaya Zemlya (“mountainous” or “vetok”), on the Mediterranean coast of France (“mistral”) and off northern shores Adriatic Sea.

Sirocco - hot and humid wind of the central part Mediterranean Sea; accompanied by clouds and precipitation.

Baku Nord - a strong cold and dry north wind, reaching speeds of up to 20 and sometimes 40 m/sec. It is observed in the Baku region both in summer and winter.

Norder is a north or northwest wind blowing in the Gulf of Mexico.

Bayamos - a strong squall wind with rain and thunderstorms south coast Cubes.

Tornadoes are whirlwinds over the sea with a diameter of up to several tens of meters, consisting of water spray. They exist for up to a quarter of a day and move at speeds of up to 30 knot The wind speed inside a tornado can reach up to 100 m/sec. Occur most often at low latitudes; l temperate latitudes can occur in summer.

Ballistic (reduced) wind is a calculated wind, which is assumed to be constant in speed and direction within a given thickness of the atmosphere and in its effect is equivalent to the total effect on the projectile (missile) of all actual winds in this thickness.

Ballistic wind calculation:

Using balloon observations, determine the actual wind at different altitudes:

The wind speed and direction in different layers are calculated using an aerometeorological tablet (AMP) or, as it is called, a Molchanov circle. The operating procedure on this tablet is always attached to it.

According to "Aviation Meteorology"

Topic 1 “Structure of the atmosphere” (1 hour).

Various classifications layers of the atmosphere.

International standard atmosphere.

Various classifications of atmospheric layers

1. Division of the atmosphere into layers, which is based on the vertical division of temperature:

a). Troposphere (0-11 km).

The temperature decreases with altitude (6.5* per 1000m): from 8*-10* (at the poles) to 16*-18* (in the tropics).

The lower layer of the troposphere (boundary, or friction layer) - up to 1-1.5 km. In this layer the influence of the earth's surface is especially pronounced.

Below the lower layer there is a ground layer (up to 200 m).

b).Stratosphere (up to a height of 50 km).

The temperature in the stratosphere is constant (-56*), but then begins to rise (up to +20*).

c).Mesosphere (up to 50-80 km).

The temperature begins to decrease (3.5* per 1 km).

d).Thermosphere (up to 800 km).

The temperature rises very quickly and reaches 100*.

d).Exosphere (more than 800 km).

Temperature above 100*C.

2. Dividing the atmosphere into layers according to air composition.

a).Homosphere is a layer where the composition of the air is constant.

b).Heterosphere is a layer where the composition of the air changes with altitude.

c).Ozonosphere - highly rarefied air, ozone layer(from 15 to 50 km).

3. Division of the atmosphere into layers based on interaction with the earth’s surface:

a).Boundary layer (1-1.5 km).

b).Free atmosphere.

International standard atmosphere.

The standard atmosphere is conditional distribution by height of the average values ​​of the main physical parameters of the atmosphere (pressure, temperature, density, speed of sound for dry and clean air permanent staff, the indicator of which is used in calculations when bringing test results to the same conditions).

GOST MSA:

H = 2km - 50 km;

latitude - 45*32 33;

t*C = 15*C (T=288.15K);

VTG (vertical temperature gradient) - 6.5* per 1 km;

P(pressure) = 760 mm Hg. Art. (1013.25 hPa);

p(air density) = 1.225 kg per cubic meter;

in this case, the readings of VTG, P, p are given at a height of H=0.

All the most important weather phenomena for a pilot develop mainly in the troposphere.

The mass of the atmosphere is 5.27x10 to the 15th power of tons.

Topic 2 “Meteorological elements

And their analysis. Meteorological codes and weather maps."

General provisions;

Meteorological elements:

a) atmospheric pressure and air density;

b) air temperature;

c) air density and humidity;

d) wind direction and speed;

e) amount, shape and height of clouds and precipitation;

f) visibility;

Weather phenomena:

a) fogs and haze;

b) icing;

c) thunderstorms and squalls;

Weather maps:

a) ground maps;

b) altitude maps.

The state of the atmosphere at a certain point in time is characterized by a number of physical quantities, which are called meteorological elements or parameters (atmospheric pressure, temperature, air density and humidity, wind direction and speed, number, shape and height of clouds).

In addition to meteorological elements, aviation meteorology also studies atmospheric phenomena (thunderstorm, blizzard, fog, etc.).

The set of meteorological elements and atmospheric phenomena observed at any point or period of time is called weather.

The main parameters of the atmosphere influence hourly fuel consumption, engine thrust, aircraft climb rate and ceiling, its stability, take-off run and mileage.

Meteorological elements.

Atmosphere pressure

This is the weight of a column of air from a given surface to upper limit atmosphere per 1 sq.cm. cross section this pillar; atmospheric pressure is measured by a mercury barometer, for aviation needs in millimeters of mercury, and for weather needs in millibars (mb). The relationship between these units is as follows: 1 mb corresponds to 0.75 mm Hg. Art. (3/4), 1 mm Hg. Art. corresponds to 1.33 MB (4/3).

Standard atmospheric pressure is 760 mmHg. Art. (at a temperature of 0* at a latitude of 45*), which is equal to 1013.25 mb.

To characterize atmospheric pressure, a concept called baric gradient is used. Pressure gradient - change in pressure per unit length (used to characterize the change in pressure with height and horizontally).

The positive pressure gradient is directed towards the pressure drop along the shortest path.

To characterize the change in pressure with altitude, a pressure stage is used. The pressure stage is the vertical distance in meters at which the pressure changes by 1 mmHg. Art. or by 1 MB, i.e. the height to which you need to rise or fall for the pressure to change by 1 unit. So near the ground you should rise by an average of 8 m so that the pressure changes by 1 mm, at an altitude of 5 km - by 15 m, and at an altitude of 18 km - by 70-80 m.

The value of the pressure level depends on pressure and temperature: with increasing pressure and decreasing temperature it decreases, with decreasing pressure and increasing temperature it increases.

Effect of atmospheric pressure on flight:

1).it is necessary to take into account the change in pressure when determining the flight altitude;

2).an increase in atmospheric pressure leads to a decrease in the separation speed;

Atmospheric pressure values ​​are plotted on a synoptic map in the form of lines of equal atmospheric pressure, called isobars.

When estimating atmospheric pressure, the barometric tendency should be taken into account, i.e. change in atmospheric pressure over the last 3 hours.

Air density

This is the ratio of the mass of air to the volume it occupies, expressed in g/cub.m. Air density can be calculated if the air pressure and temperature are known. It increases with decreasing temperature and increasing pressure, and vice versa.

Air density also depends on the amount of water vapor in the air. Water vapor density less density dry air, and therefore moist air at the same pressure will have less density than dry air. So, at a pressure of 750 mm Hg. Art. and a temperature of 20*C, the density of dry air is 1189 g/cub.m, and the density of air saturated with water vapor under the same conditions is 1178 g/cub.m, i.e. 11 g/cub.m less.

Density varies throughout the year depending on latitude, as well as changes in temperature and air pressure. In the troposphere, the air density is generally less in summer and more in winter.

With height, air density decreases. This decrease is mainly determined by changes in atmospheric pressure.

Air pressure, density and temperature are the main physical parameters, characterizing the air as the environment in which the aircraft flies.

Air temperature

This is a parameter characterizing the degree of air heating.

Air temperature is measured at H=2m with liquid thermometers.

Most countries use a centigrade scale (Celsius scale - *C), in which 0*C is the melting temperature of ice, and +100*C is the boiling temperature of water at a pressure of 760 mm Hg. In theoretical meteorology, aerodynamics and others scientific disciplines applies absolute scale temperature (T) proposed by Kelvin (K*). Temperatures on the Kelvin and Celsius scales are related by the relationship:

Т= 273.15 + t*С,

where the value 273.15 is called absolute zero temperature, and t* is the temperature on the centigrade Celsius scale.

Air temperature is a very variable weather element, depending on many factors: the amount of heat supplied at a given geographical latitude from the Sun, from the nature of the underlying surface, from the time of year and day, from atmospheric circulation, etc.

Under the influence of these factors, temperature experiences periodic (daily and annual) and non-periodic fluctuations.

The amplitude of the daily temperature variation is the difference between the maximum and minimum temperature within 24 hours.

The annual temperature range is the difference between the maximum and minimum temperatures during the year.

The correct daily temperature variation is the most heat from 13 to 15 hours local time, minimum - before sunrise.

Heating and cooling of air occurs from the Earth's surface. The air warms up from the bottom up and rises, while at the same time the colder air falls down and is compressed. As a result, air is mixed vertically.

An increase in temperature with height in a certain layer is called an inversion. A layer where the air temperature does not change with height is called isometry. Inversion and

isometry is called delay layers because they impede the vertical movement of air. These layers are regularly observed on different layers in the troposphere, especially in the cold half of the year and at night. These layers have a significant influence on weather formation. Below them there can always be clouds, poor visibility, icing, bumps, and wind shear.

The change in temperature with height for every 100m is called the vertical temperature gradient. According to the ISA, the vertical temperature gradient in the troposphere is 0.65* when rising by 100 m.

Air temperature is plotted on the weather map as solid lines. equal temperatures- isotherm.

The influence of air temperature on aviation operations is significant. Air temperature affects the required and maximum speed flight, rate of climb and ceiling, engine power and thrust, takeoff and run length, instrument readings.

Tall and low temperatures near the ground, it makes it difficult for technical staff to prepare equipment; in severe frosts, it becomes difficult to start aircraft engines.

Bad influence The operation of aircraft is also affected by sharp changes in air temperature, especially when after severe frosts a thaw is coming.

With positive deviations of air temperature from the ISA data, the flight characteristics of aircraft deteriorate, and with negative deviations, they improve.

When the air temperature near the ground is 0*C - (-3*C) ice is possible on taxiways, runways, and ground structures; When flying in clouds, precipitation, where the temperature is 0*C- (-10*C), icing occurs. When flying to air mass, where the vertical temperature gradient is greater than 0.65 * per 100 m, bumpiness is observed, thunderstorms and phenomena associated with it occur.

Air humidity

This is the degree of saturation of air with water vapor. It is an important quantity in assessing the weather, because... promotes the formation of clouds, precipitation, fog, thunderstorms, etc.

Various characteristics are used to estimate the water vapor content in the air.

Absolute humidity (a) - the amount of water vapor contained in 1 cubic meter. meter, expressed in grams.

Water vapor pressure (e) is the partial pressure of water vapor contained in the air, expressed in mmHg. Art. or mb. Numerically, both of these quantities are close to each other.

Absolute humidity is mainly taken into account in the spring and summer when forecasting thunderstorms. If a=15mb, thunderstorm should be expected; a=20mb - the thunderstorm will be with showers, and more than 23mb - the thunderstorm will be with a squall.

Relative humidity (r) - percentage the actual amount of water vapor in a given volume of air to the amount of water vapor saturating this volume of air at the same temperature, expressed as a percentage:

r =------- x 100%, where

a is the actual amount of water vapor;

A - maximum possible quantity water vapor at a given air temperature.

Maximum amount The amount of water vapor that can be contained in the air (100% relative humidity) depends only on the temperature: the higher the temperature, the more water vapor is needed for saturation, and vice versa.

On surface weather maps, instead of the air humidity values ​​discussed above, Dew point(t*d) is the temperature at which the air reaches a state of saturation at a given water vapor content and constant pressure. The dew point is equal to the air temperature at relative humidity 100%. Under these conditions, condensation of water vapor occurs (transition of water vapor into liquid state) and the formation of clouds and fogs. The drier the air, the greater the difference between the air temperature and the dew point (dew point deficit - delta td). Cooling air containing water vapor can cause sublimation (the transition of water vapor into a solid state, bypassing the liquid phase).

Dew point deficits are plotted on absolute topography maps and are used to determine the potential for cloud formation. At altitudes up to 5 km, we can assume the presence of 10 points of clouds with deficits of 0*, 1*, 2*. Based on the deficit, one can determine the level of water vapor condensation, i.e. level where air reaches 100% saturation:

hк= 123 (t*C-t*d),

where hk is the condensation level.

Water vapor plays an exceptional role important role in determining the meteorological conditions of flight in the troposphere. The presence of water vapor in the atmosphere is a necessary condition formation of clouds, precipitation, fog. Atmospheric phenomena- thunderstorms, snowstorms, icing, etc. optical phenomena, like rainbows, halos, crowns, are also inextricably linked with the presence of water in the atmosphere. Such an important meteorological element as visibility is in most cases determined by the presence in the atmosphere of tiny drops of water, ice crystals, or both.

Wind direction and speed.

Wind is the horizontal movement of air relative to the earth's surface. But the air flows are not strictly horizontal, because... There are almost always vertical components to these movements.

Wind is a vector quantity and is determined by two components: direction and speed.

Wind direction is the azimuth of the point on the horizon from which the wind is blowing, measured in degrees.

Wind speed - the speed of air movement over a selected time interval. Usually measured in meters per second. For aviation calculations, wind speed is expressed in kilometers per hour. (1 m/sec = 3.6 km/h). The concept of wind force is inextricably linked with wind speed:

2-3 m/sec - weak (slightly felt);

4-7 m/sec - moderate (thin tree branches sway);

10-12 m/sec - strong (thick tree branches sway);

More than 15 m/sec - storm;

More than 20 m/sec - storm;

30 m/sec - hurricane.

The wind is not a stable current and changes both in speed and direction over short periods of time. This wind variability is especially pronounced near the earth's surface and is directly related to the turbulent state of the air flow.

Air movement occurs under the influence of the rotational force of the earth (Coriolis force), the pressure gradient force arising due to uneven distribution horizontal air pressure, friction and gravity.

Under the influence of these forces in a layer up to 1000-1500m, the time vector is directed towards the isobar under acute angle, the magnitude of which is greater over land and less over the sea, is greater at low latitudes and decreases towards the poles.

In a cyclone in the Northern Hemisphere, the winds at the ground blow in a spiral from the periphery to the center counterclockwise, in an anticyclone - in a spiral from the center to the periphery clockwise.

Wind speed and direction depend on the height above the ground, geographical area, time of year and day, on pressure distribution.

The diurnal variation of wind speed near the ground is most clearly expressed over land and is almost imperceptible over the sea. It is more pronounced in the warm half of the year and in clear weather, weaker in cold and cloudy weather.

With increasing altitude, the wind speed increases on average, and at an altitude of 500 m it is almost twice as high as at the ground; in the friction layer the wind turns to the right, and in the free atmosphere it blows almost strictly along the isobars (if you stand with your back to the wind, then less pressure will be on the left).

The wind has great importance for aviation:

The wind significantly affects takeoff and landing; with a headwind, the length of the takeoff and run is reduced;

When there is a crosswind, forces arise that make it difficult to control the aircraft. So, for example, if the wind blows to the right of the take-off direction, then an additional lift force appears on the right plane, and on the left it decreases, resulting in a heeling moment; in addition, the crosswind creates a force tending to turn the aircraft relative to its longitudinal axis, and therefore away from the runway axis;

More great difficulties a side wind is created when landing an aircraft, because makes it difficult to accurately maintain the aircraft on the descent glide path and during the runway run;

Wind significantly affects aircraft navigation (correction for wind is necessary when maintaining direction);

The wind causes chatter, dust storms, blowing snows that impair visibility and complicate the takeoff, flight, and landing of aircraft.

When assessing specific weather conditions, it is necessary to take into account local winds that arise under the influence of local physiographic and thermal conditions.

Serious difficulties for piloting an aircraft on the descent glide path, during takeoff, and landing are caused by

wind shear.

Wind shear is a change in wind direction or speed, or both, horizontally, or one layer of the atmosphere relative to another vertically.

There are horizontal and vertical wind shears:

Vertical wind shear (the vertical component of the wind gradient) is a change in the direction and speed of the wind with height (for example, at H=200m the wind direction is 280* and its speed is 18 m/sec, and at H=100m the wind direction is 80* and the speed is 8 m /sec).

Horizontal wind shear (horizontal component of the wind gradient) is a change in wind direction and speed at different horizontal points at the same height.

To assess the intensity of wind shear, you should use the terms and their numerical categories that are recommended by ICAO (see Table 1).