One of the versions of the plane crash in Rostov-on-Don, which occurred on March 19, is called a rare weather phenomenon - a jet stream of air. What it is and how it affects aircraft flights, read in the "Question and Answer" section.
What is a jet stream?
A high-altitude jet stream is a strong wind in the form of a narrow air stream in the upper troposphere or lower stratosphere. It is characterized by high speeds (usually more than 30 m/s on the axis) and gradients of more than 5 m/s per 1 km in height and more than 10 m/s per 100 km horizontally. Simply put, a jet stream is a fairly narrow, fast-moving stream of air that looks like a jet (hence the name jet). This jet may be thousands of kilometers long, hundreds of kilometers wide, and several kilometers thick. And inside it rages a hurricane with a wind speed of 100 to 900 kilometers per hour. At the same time, there are no changes in the atmosphere around this "pipe".
What causes jet stream?
According to scientists, this is due to the uneven heating of the Earth, during rotation around the Sun. Warm winds blowing from the equator meet cold winds from the poles and a large difference in pressure occurs. It is in such regions that jet streams are formed. These currents are the dividing line between cold and warm regions. And the greater the temperature difference, the stronger these winds.
Why is the jet stream dangerous for aircraft?
A jet stream usually occurs high above the ground - at an altitude of 9144 to 18,288 m. Therefore, they are not dangerous on the ground. But pilots know them very well. At the beginning of the 20th century, pilots reported that they sometimes encountered a kind of air wall, when trying to fly into which the planes hovered in place. Later, scientists gave the name to this phenomenon "jet flow".
According to Wikipedia, high-altitude jet streams are dangerous for aviation due to strong turbulence.
These phenomena are also dangerous during the landing of the aircraft. Since, in an aircraft caught in a jet stream, dynamic controllability can significantly deteriorate.
How do modern pilots use the jet stream?
Tailwinds help aircraft save travel time and fuel. For example, pilots use the North Atlantic jet stream when flying on the New York-London route. On the way back, they have to fly through Iceland and the south of Greenland to avoid the oncoming jet. Approximate calculations: when flying at a speed of 600 km / h in a tail jet stream, the speed of which is 360 km / h, the ground speed of the aircraft increases to 960 km / h. In this case, the aircraft will cover a distance of 600 km in 36 minutes instead of an hour. Accordingly, fuel savings will be about 50%
Why is the jet stream over Rostov a rare occurrence?
The effect of wind on aircraft movement parameters is most significant at high wind speeds, especially in the area of jet streams (JTs).
ST is the transport of air in the form of a narrow current with high velocities, usually in the upper troposphere to the lower stratosphere with an axis near the tropopause. The maximum wind speed (30 m/s and >) is observed on the ST axis. The change in wind speed in the ST area is usually 5-10 m/s per 1 km of altitude and 10 m/s and > 100 km in the horizontal direction.
STs are formed in the zones of closest approach of warm and cold air masses, where significant horizontal pressure and temperature gradients are created. Since the greatest temperature contrasts in the zones atmospheric fronts observed in the hall. half of the year, then during this period STs are most active.
The navigational significance of jet streams can hardly be overestimated. On the one hand, cirrus and cirrocumulus clouds and intense turbulence often occur in the ST zone, and on the other hand, a strong wind in the ST zone significantly changes the aircraft speed.
Intense turbulence is observed mainly on the cold (cyclonic) side of the ST, where the temperature and wind gradients are greater. On the ST axis, strong turbulence is much less common.
If the flight in the ST zone takes place against the wind, then the ground speed decreases sharply, if it goes upwind, it increases. When flying long distances, you can use ST to reduce flight time and to increase the flight range. Currently, there are methods that allow, based on wind field data, to propose the most advantageous route along which the aircraft will arrive at the destination or from least cost time, or with the lowest fuel consumption. All of the above testifies to the great navigational significance of ST.
22. Classification of air masses (a) geographical ( arctic, temperate and tropical air, each of the VM is continental or marine, depending on the conditions of formation); b) according to the conditions for the development of convection (stable and unstable).
a) Depending on the position of the source of air formation in one of the main thermal belts of the globe and taking into account the nature of the underlying surface (ocean or mainland), the following types of air masses are distinguished:
Arctic or Antarctic air (AB) - marine (mAB) and continental (cAB) - is located in the northern and southern polar regions of ice and snow;
Air of temperate latitudes (HC) - marine (mHC) and continental (cHC) - is located in temperate latitudes;
Tropical air (TV) - marine (mTV) and continental (kTV) - is located in the areas of the trade winds of the northern and southern hemispheres;
Equatorial air (EV) - located near the equator between the northern and southern trade winds.
Sea air has high humidity. It is around 80% everywhere. In addition, there are differences in the temperature regime. AT summer time in temperate latitudes it will be colder than continental, and warmer in winter.
Arctic and Antarctic air, due to the predominance of ice fields and land in high latitudes, rarely maritime arctic (MAB). They do not divide into sea and continental equatorial air, since over land and over the sea it is equally warm and humid due to the huge amount of precipitation.
b) An air mass is called stable if there are no conditions for the development of ascending air movements (convection). Vertical movements can only occur in the form of dynamic turbulence with horizontal air movement. This air mass usually includes warm masses.
Unstable is an air mass in which there are conditions for the development of ascending air movements (convection). Cold masses are usually unstable.
23. Wind - direction and speed, classification: weak, moderate, strong, storm, changing, gusty, squall.
Wind- this is a horizontal (advective) movement of air relative to the earth's surface, characterized by direction and speed.
Direction given by an angle (or rhumb δ=22.5 0), counted from the north direction clockwise
Speed value set by the plumage on the arrow (small feather - 2.5 m/s, large feather - 5 m/s, black triangle - 25 m/s)
According to the magnitude of the speed, the wind is distinguished:
1) < 3 м/с – слабый
2) 4-7 m/s - moderate
3) 8-14 m/s - strong
4) 15-19 m/s - very strong
5) 20-24 m/s - storm
6) 25-30 m/s - severe storm, hurricane.
7) The changing wind- in 2 minutes the direction changes by more than 1 rhumb.
8) Gusty– in 2 minutes the wind changes by 4 m/s or more.
9) Squall– short-term sharp increase in wind up to 20 m/s and more with a significant change in direction.
24. Local winds: hair dryer, bora, breeze, intramass squall, blood clots, tornadoes, tornadoes. aviation conditions.
local winds - winds characteristic of certain areas, associated with the peculiarities of local orography, land-water proximity, etc.
1. Breeze - this is the wind coastline seas and small lakes with a sharp diurnal change of direction (layer 1-2 km).
night breeze: daytime breeze:
2.Fen (garmsil) - a warm, dry gusty wind blowing from the mountains into the valley.
Peculiarities:
1. Significantly increases the temperature (by 30 0 in a few hours) and lowers the humidity (up to 4-5%).
2. Duration - from several hours to several days.
3. Causes a strong storm of the sun.
3. Bora – strong (V> 20 m/s) cold gusty wind blowing from low mountain ranges towards the warm sea.
4. Flurries - sharp short-term wind amplification (up to 20 m/s). They are intramass (in convective Cb) and frontal (in several places along the HF, 2nd kind - a line of squalls).
P.S. Ci - cirrus, Cs - cirrostratus, Cb - cumulonimbus, Cu - cumulus,
Ns - stratified rain, St - stratified.
Squall Gate (HF)- a vortex with a horizontal axis that occurs in front of a thundercloud.
5. Thrombus (tornado, tornado) - special small-scale eddies (d=1-100 m, h=1 km, travel speed - 20-30 km/h, lifetime - 1-10 min, pressure in the center is reduced by 10-100 hPa).
Peculiarities:
1. Arises in front of a thundercloud and penetrates from above to the Earth itself;
2. Observed in temperate and tropical latitudes in warm and humid unstable stratified VM;
3. Rotation of air around the axis as in a cyclone with v=70-100 m/s;
4. Presumably - a kind of thunderstorm squall;
5. The energy of a typical tornado with a radius of 1 km and an average speed of 70 m/s is equal to the energy of a standard atomic bomb of 20 kilotons of TNT.
6. Mountain-valley winds (up to 10 m/s) - are expressed in the warm season, fill the entire section of the valley, vertical thickness - the average height of the ridges.
25. Cyclonic activity. Stages of development of cyclones. formation of anticyclones. Flight conditions in different parts of cyclones and anticyclones, in the zone of atmospheric fronts.
Cyclone – region reduced pressure, bounded by closed isobars with minimum pressure in the center.
Anticyclone – region high blood pressure, bounded by closed isobars with maximum pressure at the center.
According to the baric wind law:
1) In a cyclone, the circulation is counterclockwise; in an anticyclone, it is clockwise.
2) The wind speed in a cyclone is on average greater in magnitude than in an anticyclone.
NEED TO COMPLETE
26. Weather minimums.
Minimum weather - a term denoting the extreme weather conditions under which a trained aircraft commander is allowed to fly, operate the aircraft and use the airfield for departure and landing.
Minimum weather defined:
Cloud base height (decision height)
Visibility (visibility on the runway)
P.S. Runway visibility — the maximum distance within which the pilot of an aircraft on the center line of a runway can see its pavement markings or lights delimiting the runway or marking its center line.
Decision Height - the specified relative height at which the go-around maneuver should be started if, before reaching this height, the aircraft commander did not establish visual contact with the landmarks to continue the landing approach, and also if the position of the aircraft in space or the parameters of its movement are not provide a safe landing.
The weather minimum includes the minimums of:
airfield
aircraft
Commander of the Armed Forces
Type of aviation work
Aerodrome minima depend on the geographical location of the aerodrome and its equipment with landing systems.
Consists of minimums:
- for takeoff- these are the minimum allowable values of runway visibility and cloud base height at which it is allowed to take off on an aircraft of this type.
- for landing- the minimum allowable values of runway visibility and decision heights at which it is allowed to land on an aircraft of this type.
- takeoff training (1)
- training for landing(same specifications as for item (2) only for training flights.
Aircraft Minimum due to the availability and quality of special navigation equipment available on board the aircraft.
Consists of minimums:
- for takeoff- the minimum allowable runway visibility values that allow safe takeoff on an aircraft of this type.
- for landing- the minimum allowable values of runway visibility and decision heights that allow a safe landing on an aircraft of this type.
Aircraft commander minimum are determined and determined by the personal training of the pilot.
Consists of minimums:
- for takeoff- the minimum allowable value of visibility on the runway, at which the commander is allowed to take off on an aircraft of this type.
- for landing- the minimum allowable values of visibility on the runway and the height of decision-making (height of the base of the clouds), at which the commander is allowed to land on an aircraft of this type.
- for flight under the rules of visual flight and special rules visual flight– the minimum allowable values of visibility and height of the cloud base, at which the commander is allowed to perform visual flights on aircraft of this type.
Minimum type of aerial work - the minimum allowable values of visibility and height of the lower boundary of the clouds, at which it is allowed to perform aerial work using the flight rules (visual or instrument) established for this type of work.
- first category (60m), runway visibility (800m).
- second category is the height of the lower boundary of the clouds (less than 60m, but not less than 30m), runway visibility (less than 800m, but not less than 400m).
- third category is the height of the lower boundary of the clouds (less than 30m), and runway visibility (less than 400m).
Divided by:
III-A- runway visibility (at least 200m).
III-B- runway visibility (at least 50m).
III-C- runway visibility (equal to 0 meters).
P.S. During takeoff and landing, 3 weather minima are taken into account: the airfield, the aircraft and the aircraft commander, from these three greatest.
With a minimum airfield of 100x1000, a minimum of aircraft 50x500, a minimum of an aircraft commander 80x1500, then this pilot on this the plane can land on this airfield in weather no worse than 100x1500.
27. Influence of temperature and air density on engine thrust, required speed, aircraft ceiling.
The dependence of available thrust on meteorological conditions also determines their influence on other important aircraft performance characteristics - maximum flight speed, rate of climb, aircraft ceiling, as well as fuel consumption.
One of the most important performance characteristics of an aircraft is its ceiling- the highest altitude that an aircraft can climb in a certain flight mode.
Distinguish:
theoretical The ceiling is the height at which the excess thrust and the vertical speed are zero.
Practical The ceiling is the height at which the maximum vertical speed for jet aircraft is 5 m/s, and for piston aircraft - 0.5 m/s.
static ceiling is the highest level flight altitude at a constant speed.
dynamic the ceiling is the highest height achieved by using the kinetic energy of the aircraft, i.e. due to loss of speed.
At these altitudes, fuel consumption decreases and flight range increases. If the ceiling of the aircraft allows you to fly above the tropopause, then this, in addition to the above advantages of flying near the ceiling, helps to overcome the zones of thunderstorm activity, intense turbulence, icing and other adverse meteorological conditions observed in the troposphere. However, it should be borne in mind that near the ceiling, the aerodynamic qualities of the aircraft deteriorate, since high angles of attack are used here, stability and controllability are lost. The ceiling of an aircraft depends on the physical state of the atmosphere. For most modern aircraft, it exceeds the height of the tropopause.
28. Dangerous weather phenomena for aircraft (indicate where the specified phenomenon is formed and what is the danger for flights): Atmospheric turbulence (thermal, orographic, dynamic) and aircraft turbulence. Clear sky turbulence (where is it observed?). Wind shear and its effect on aircraft takeoff and landing. At what wind shear is takeoff and landing prohibited? Aircraft icing, methods of struggle. At what rate of ice buildup on aircraft bearing surfaces is icing considered severe? Thunderstorm activity. Classification of thunderstorms, squall. Static electricity.
Turbulence
Occurs during thunderstorms, at AF, during vertical wind shear ∆v/∆h (during radiative, advective and orographic inversions), in ST zones with a clear sky (CAT on the cyclonic periphery), in mountainous areas (orographic turbulence), in cumulus clouds, in unstable VMs.
Causes overloads (ratio of lift to gravity), impairs aircraft controllability
According to the conditions of education, there are:
1) Thermal turbulence (unstable VM)
2) Dynamic turbulence:
On surface AF with horizontal gradients T more than 2 C per 100 km, horizontal gradients of wind speed - more than 20 km/h per 100 km,
Cloudiness
Near the main (climatological) fronts (PVFZ, ST), more often these are TYN, synoptic situations with significant convergence or divergence of isohypses
3) Mechanical (orographic) turbulence:
(as a result of air friction on the underlying surface), on the windward side often - wind shear, on the leeward - "rotor"),
· With stable stratification and v>10 m/s, increasing with height - mountain waves with a wavelength of 5-50 km, h=(3-4) Hchr, with high humidity - lenticular clouds.
Dimensions and frequency of turbulence zones
85-90% of cases: Δz <1000 м,
(In temperate latitudes Δz <500 м, Δl~40 km 80%
T / o the probability of getting into a bumpy when changing flight levels is higher than in level flight.
In the troposphere: greatest repeatability of turbulence in the 0-2 km layer (thermal and mechanical turbulence) and in the 8-12 km layer (dynamic).
Chatter intensity
Weak - Δn < + 0.5 g at flight level
and Δn < + 0.3 g on glideslope
Moderate - Δn < (0,5-1) g на эшелоне
and Δn < ( 0.3-0.4) g on the glide slope
Strong - Δn> 1 g at flight level
and Δn> 0.4 g on glideslope
Electrification
The defeat of the aircraft by e/st discharges occurs in Cb, Ns, Sc, St - at E> 10 6 V / m
Frequent in the HF zone of the 1st kind, in Cb, not reaching the stage of a thundercloud;
Weak electrization in Ci, St (TF, HF).
The occurrence of radio interference
The yaw of the arrows of radio compasses,
Failures of airborne radars, antennas,
Skin damage
Jet streams of varying intensity and frequency are observed over almost all regions of the globe. According to the latitudinal zones and the height of the axis, the following types of jet streams are distinguished: extratropical, subtropical, equatorial and stratospheric. Each of them has its own characteristic features that distinguish them from each other.
extratropical jet streams are integral part high-altitude frontal zones formed between high warm anticyclones and high cold cyclones. They are more mobile, and their intensity undergoes continuous changes. The height of the maximum wind is most often at the level of 8-10 km in winter and 9-12 km in summer. The wind speeds on the axis of the jet fluctuate over a wide range, depending on the magnitude of the horizontal temperature gradients in the underlying air layers. Most often, maximum wind speeds reach 150-200 km / h, but in individual cases exceed 300 km/h or more. The value of temperature contrasts in the frontal zone, in layer 300 above 1000 mb, usually varies within 10-15°, but sometimes exceeds 20°.
In winter, the contrasts of temperature and wind speeds are on average greater than in summer.
Subtropical jet streams are formed on the northern periphery of subtropical high and warm anticyclones. They are less mobile than extratropical ones and undergo significant movements depending on the nature and intensity of interlatitudinal air exchange; the axis of the jet is located at the level of 11-13 km. In winter and especially in summer, temperature contrasts up to the upper troposphere increase with altitude. During the formation and strengthening of the jet stream, the tropopause undergoes a rupture. The axis of the jet is usually located between the tropical tropopause at altitudes of 16–17 km and the mid-latitude tropopause at altitudes of 9–12 km.
In winter, the jet is mostly between 25-35°N. w, in summer - to the north by 10-16 °, and in some places even more. Average wind speeds on the axis of the jet reach 150-200 km/h. The distribution of wind speeds along the latitudes is different. The maximum wind speeds are observed in winter over the eastern margins of the continents and adjacent parts of the oceans. In particular, over the Japanese islands, wind speeds often exceed 300-400 km/h. The subtropical jet is most weakly expressed over the eastern regions of the Atlantic and Pacific oceans. It intensifies here during meridional transformations of the atmospheric thermobaric field, accompanied by cold advection to low latitudes.
equatorial eastern jet streams are formed on the southern periphery of high subtropical anticyclones (in the northern hemisphere). Western equatorial jets were discovered in winter at 80° W. d. and 11 ° with. sh. at the level of 200 mb. Their average speed is not less than 100 km/h. In summer, their intensity increases, at latitudes of 10-20 °, at the same level in summer, eastern equatorial jets were found in various parts of the northern hemisphere. They are especially intense in southern Asia. Weak eastern jets in the equatorial zone were also found on
Pacific Ocean. The strongest eastern jet is located on the southwestern periphery of the summer high anticyclone over North Africa and Arabia. Here at 15-20° N. sh. and 45°.c. the average wind speed at the level of 150 mb exceeds 100-120 km/h.
Stratospheric jet streams have been detected in winter at altitudes of 25-35 km between 50 and 70°N. sh. Due to the continuous radiation and cooling of air in the ozone layer under the conditions of the polar night, a high and cold cyclone is formed beyond the Arctic Circle with large temperature contrasts at the periphery. Strong westerly winds arise in the zone of these temperature contrasts. The greatest intensification of the jet occurs in December - January. In March, westerly winds at these heights weaken and at the end of May they switch to easterly ones.
The transition of the wind to the east occurs due to the establishment of a new regime of radiant heat transfer in the ozone layer in polar day conditions. As a result of warming air in summer, in In contrast to winter, a powerful anticyclone appears over the Arctic regions at altitudes of 30-40 km. The stratospheric eastern jet stream is located on the southern periphery of this anticyclone. The maximum jet velocities are noticeably lower than the winter stratospheric western jet stream.
Thus, the formation of western and eastern jet streams in the stratosphere is seasonal in nature and is determined by radiation conditions that leave a certain imprint on the thermal field of the season. Shown in fig. 19 and 20, the curves of temperature distribution with height above different latitudes, as well as the average temperature differences between extreme seasons along different meridians (see Figs. 22 and 23), explain the reasons for the formation of a stratospheric jet stream in the cold season and an eastern one in summer. The temperature distribution curves with height show that in winter the largest interlatitudinal temperature differences occur in the surface layer. The temperature differences decrease with height, and near the surface level of 200 mb they reach a minimum. Here in the atmosphere between the equator and the pole there is a position close to the min isotherms. In summer, the interlatitudinal temperature differences also decrease with height and reach a minimum near the surface level of 200 mb. Above these levels, the temperature increases again with height in winter and summer.
According to the conditions of the radiation regime in the lower stratosphere, the zone of the greatest horizontal gradients, like the jet stream, should encircle the globe between 50-70 ° N. and yu. sch. However, according to the temperature and pressure distribution data, seasonal jet streams in the stratosphere in winter are not located strictly along latitudes, but to a large extent repeat the structure of the troposphere thermobaric field known from average monthly maps of baric topography (OT 500 1000).
On fig. 63 shows the average absolute surface topography of 25 mb for January over North America.
From a comparison of Fig. 63 (AT 25) with fig. 37 (AT 500) it is easy to establish on both maps a close similarity in the configuration of isohypses (on map AT 25 the heights are indicated in feet). However, the density of the isohypses and, consequently, the velocities of the currents are much greater at the surface of 25 mb, which is explained by the increase in the temperature difference between the middle and high latitudes in the lower stratosphere.
In July, the picture is somewhat different (Fig. 64). On the same surface, 25 mb above high latitudes, there is a high-pressure region, on the periphery of which an eastern jet stream is formed. The highest jet velocities are observed between 55 and 75° N. sch. Here they are noticeably smaller than in winter. The transition of western winds to eastern ones occurs in the layer between the levels of 18 and 22 km. Therefore, it is natural that the field structure of AT 25 and AT 500 is completely different. At surface levels of 500 and 300 mb, the main direction of transfer is west-east, and at levels of 50 and 25 mb, on the contrary, east-west. Despite the sharp difference between the structure of the field AT in the troposphere and stratosphere, the influence of the lower layers of air on the formation
field AT 25 is very significant. In particular, over the tropospheric ridge over the west of North America (Fig. 64), the anticyclone is more intense, and over the tropospheric trough it is rather weak.
Consequently, the formation of the average seasonal field of the geopotential in the stratosphere, at levels 25-30, is significantly affected by the temperature field of the troposphere, due to the influx of heat from the underlying surface. Moreover, daily high-altitude weather maps show that large baric formations, clearly expressed in the troposphere, are also found at altitudes of 25-30 km. This indicates that the nature of the circulation of the atmosphere, represented by mapsATin the middle and upper troposphere, it slowly weakens with height and the main air currents cover a significant thickness of the stratosphere.
On fig. 65-67 maps of the absolute topography of surfaces 500, 100 and 30 mb during the night of December 7, 1957 are presented. From their comparison, it can be determined that the features of the pressure field and air currents in the middle troposphere are well pronounced at the surface level of 100 mb, and partially even at the level 30 mb.
In particular, traces of a high cold cyclone over the Balkans and Asia Minor and a warm anticyclone over the Atlantic are found at a level of 30 mb, i.e., at heights of about 24 km.
In summer, due to the warming of the air in the stratosphere, it is more difficult to detect common features between the baric field in the troposphere and at the level of 30 mb.
The main types of currently known jet streams and their features have been considered above. In addition to the main species, there is a division of them according to additional features, such as division into frontal and non-frontal, continental and oceanic, etc.
The division of jet streams into frontal and non-frontal ones is devoid of a serious basis. Any jet streams are associated
with atmospheric fronts, with the only difference that in some cases the fronts are easily detected near the surface of the earth, while in others they are blurred.
However, in both cases, the position of atmospheric fronts can always be determined in the temperature field in the troposphere.
Very often, fronts near the earth's surface are washed out in the subtropics, since the frontal cold air here quickly warms up and loses its initial properties. This was the reason for classifying the subtropical jet stream as nonfrontal. In fact, in the system of a subtropical jet, in the zone of greatest temperature contrasts, one can always find a front, even if it is blurred in layers close to the earth's surface. The process of frontal erosion at low latitudes can be traced from daily surface and high-altitude weather maps. Fronts are eroded especially quickly in the warm season over land. An analysis of observational data has shown that only the lower layers of tropospheric air are rapidly heated by vertical turbulent transport. With height, the transformation process weakens. Therefore, the temperature difference in the upper troposphere and the jet stream caused by it persist for a long time. Fronts found in the stratosphere are also determined by temperature contrasts. Stratospheric jet streams are closely related to the location zones of these frontal zones and fronts.
The division of jet streams into oceanic and continental is also not justified. The basis for this division was the difference in the increase in the speed of currents from the level of the gradient wind to the jet axis over the oceans and continents. It was found that in the system of jet streams over the North Atlantic, the wind increases with height by a smaller number of times than over northwestern Europe. However, later it was found that this phenomenon is local. In particular, near the western coast of the North Pacific Ocean the increase in wind with height is more intense than over the adjacent territory of the Asian continent.
In conclusion, we present the layouts of all types of jet streams over the northern hemisphere in winter and summer (Figs. 68 and 69). They are built on the basis of analysis of the distribution of jet streams in recent years.
From fig. 68 and 69 it can be seen that the subtropical jet streams are the most powerful and their frequency is most clearly expressed on the continents. Over the eastern parts of the oceans, a strong subtropical jet stream appears sporadically, mainly in winter, during cyclonic transformation of high-altitude deformation fields and isolation (blocking) of high cyclones in the Azores region over the Atlantic and northwest of California - over the Pacific Ocean. Sporadically emerging jet streams are shown in the diagrams by dashed lines, and the zones of intraseasonal jet movements are shown by hatching.
In southeast Asia and North America, extratropical jets usually merge with subtropical ones and form a wide wind zone with the jet axis at a level of 10–13 km in the south and 8–10 km in the north of the zone (Fig. 68).
In accordance with the large temperature contrasts, the most powerful jets in winter are most often observed over these areas, as well as over Arabia, North India and the British Isles. In a number of places, the diagrams show data on the prevailing heights of the jets and the average maximum wind speeds in them. The strongest subtropical jet streams are observed in winter over the Japanese Islands and the east of South China, where average wind speeds at altitudes of 10-13 km reach 260-320 km/h. High wind speeds here are explained by significant horizontal temperature contrasts in the troposphere due to the strongly cooled mainland of Asia and adjacent warm waters Pacific Ocean and intense cyclonic activity.
In similar conditions is the southeastern part of North America and, in part, the area between Iceland and the British
islands where strong jet streams are constant in all seasons of the year.
The predominant western direction of currents is inherent in subtropical and extratropical jets. However, in accordance with the transformations of the thermobaric field of the atmosphere, extratropical jet streams are subject to significant interlatitudinal displacements. The ramifications of the extratropical jets over Europe and Lanya and other regions indicate that they are not as constant here as the subtropical jet streams.
Note that two jets are found over Europe and Western Asia in winter, while over Far East and often over the eastern half of North America, as a result of the merger, only one powerful jet stream is formed, this is explained by the distribution of continents and oceans with the corresponding conditions of heat inflow and the formation of the temperature field of the troposphere. The cyclonic activity developing under these conditions contributes to the intensification of the subtropical jet stream. The diagrams also show stratospheric and equatorial jet streams. Stratospheric western jet streams in winter are located at altitudes of 25-30 km.
In summer, the position of the jet streams noticeably changes. As follows from Fig. 69, the zone of subtropical jet streams everywhere shifts to the north by 10-15 ° of the meridian, and near the equatorial zone, eastern equatorial jet streams appear in places. In particular, over South Arabia, the average speed of the eastern jets at the level of 13-15 km reaches more than 100 km/h. Weak easterly currents are observed at 20-25 0 s. sh. on the Pacific Ocean.
Subtropical jet streams are well expressed over North America, Western and Central Asia. They are much weaker over the Japanese islands compared to winter. Extratropical tropospheric jets are observed over Europe, North America and northern Asia.
Finally, the same summer diagram shows the stratospheric eastern jet stream at a level of 25–30 km. It arises in the warm season in connection with the establishment in the lower stratosphere of a new regime of radiant heat exchange under polar day conditions.
The speeds of air currents at heights depend mainly on the nature of the temperature field of the underlying air layers. The greater the horizontal temperature gradients in the system of the altitudinal frontal zone, the stronger the jet stream, indicating the presence strong winds in this zone. In other words, the main role in the formation and evolution of jet streams is played by the temperature distribution in the atmosphere and the emerging horizontal temperature gradients.
Jet streams, causally associated with high-altitude frontal zones, arise, intensify or weaken due to the emergence and destruction of tropospheric fronts. In the first case, as a result of the approach of cold and warm air masses, the horizontal gradients of temperature, pressure, and wind speed increase. In the second case, when cold and warm air move away from each other, the temperature and pressure gradients decrease, and the winds weaken.
Jet streams originate in the troposphere and stratosphere. In the troposphere, they are almost constantly observed in the subtropical zone of the northern and southern hemispheres: in winter between latitudes 25 and 35°, in summer between 35 and 45°. Jet streams in the troposphere very often arise and develop in extratropical latitudes, up to the Central Arctic and Antarctic. In accordance with the areas of their origin in the troposphere, subtropical and extratropical jet streams are distinguished.
The highest wind speeds in the troposphere are usually observed near the tropopause. Data on the distribution of wind at heights show that the highest speeds are observed most often under the tropopause and less often above the tropopause. In the stratosphere, they are observed from time to time under certain circulation conditions in winter at altitudes of 25-30 km.
Tropospheric jet streams are observed over almost all parts of the globe, but not everywhere with the same frequency. There are, for example, areas where, at altitudes of 9-12 km, the maximum speeds in the jet almost always exceed 200 km/h. In particular, such areas include the Pacific coast-Asia at a latitude of 30-40 °. Here, especially over the southeastern part of China and the Japanese islands, for 6-8 months, air flow speeds (mainly westward) exceeding 200 km/h at altitudes of 9-12 km are common.
Strong jet streams continuously arise near the eastern coast of the United States and often over Canada. Over Europe, jets are most often formed in the area of the British Isles.
Areas of high recurrence of jet streams coincide with areas of large horizontal temperature gradients. Therefore, the areas of greatest frequency of jet streams in winter lie at the junction of the cold continents of Asia, North America, and Greenland, on the one hand, and warm oceans, on the other. A high frequency of subtropical jet streams is characteristic of northern Africa and South Asia.
The low frequency of tropospheric jet streams occurs in regions with a more or less uniform underlying surface. These are oceans south of 30-40 ° N. sh. and north of 30-40 ° S. sh., the northern parts of the continents Asia and America with the adjacent regions of the Arctic, and in the southern polar region - Central Antarctica.
Jet streams are usually depicted in the horizontal and vertical planes. In this case, wind speeds are represented by isotachs, i.e., lines same speeds wind.
On fig. Figures 69 and 70 show maps of the absolute baric topography of the 200 mb surface for various periods. The first card refers to the middle of winter, the second - to the middle of summer. The baric topography map of the 200 mb surface (altitude about 12 km) reflects the distribution of maximum wind speeds in the upper troposphere and lower stratosphere. It is easy to see that against the background of rare isohypses, a zone of their thickening is clearly visible, encircling the entire northern hemisphere. In these zones, the highest wind speeds are observed - jet streams. In places where the jets merge, an increase in wind speeds is noted. Where the branching of the jets occurs, a weakening of the wind is observed.
In particular, on the evening of January 5, 1956 (Fig. 69), strong jet streams arose at the confluence of the southwestern and northwestern air currents, between Iceland and Scandinavia. The same strong jets are easy to detect over the South and Southeast Asia, Alaska, etc. It should be noted that the thickening of isolines, i.e., high wind speeds, in the winter months can almost always be found south of 40 ° N. sh. (subtropical jets), while in temperate and high latitudes, especially over the USSR, jet streams weaken, break up and reappear in connection with the emergence and development of cyclones and anticyclones.
In summer, south of 40 ° N. sh. jet streams are very rare. They are more often found in temperate and high latitudes. A typical distribution of jets in the northern hemisphere in summer is shown in Fig. 70. As can be seen, the zone of thickening of isohypses and strong winds on the isobaric surface of 200 mb on July 31, 1956 passed through the temperate latitudes of the northern hemisphere, and the winds were weak over low latitudes and the Arctic. However, on some days, jet streams can be intense at high latitudes as well.
The spatial structure of jet flows is also depicted in a vertical plane perpendicular to the flow direction. These are the usual vertical sections of the atmosphere with isotherms and isotachs, sections of fronts and tropopause. On fig. 71 and 72 show two typical examples of vertical sections of jet streams for winter and summer. These sections show subtropical and extratropical jets. In the center of the jet streams, letters indicate the main directions of air currents.
On the average monthly vertical section of the atmosphere, built according to observational data for January 1957-1959. up to approximately 25 km between the equator and the North Pole (Fig. 71), two western jet streams are depicted with axes located at levels of 10 and 12 km. Average maximum wind speeds on the axis of the subtropical jet (left), reaching 180 km/h, were observed over Iraq. The second jet (on the right) was over Moscow at a level of about 9 km. Here, the average maximum wind speeds were 100 km/h. Meanwhile, at the surface of the earth, the average wind speeds did not exceed 10-20 km/h. In the summer (August 29, 1957), the subtropical jet was over Transcaucasia, and the extratropical jet was over Moscow. In the first jet, the maximum speed reached 140 km/h, in the second - 120 km/h. Despite the typical nature of the sections presented here, in some periods the location of the jet streams may be different.
It should be noted that due to the significant discrepancy between the horizontal and vertical scales, the usual oblate shape of the jet is not expressed in the presented sections. However, if we take into account that, for example, in the southern jet system in Fig. If the distance between the low and high positions of the isotachy is 100 km/h, i.e., approximately 10 km vertically and more than 2000 km horizontally, it will become apparent that the jet has the shape of a rather flattened ellipse. The relationships between vertical and horizontal extent are similar in other jet streams.
The characteristic structural features of high-altitude frontal zones and jet streams do not undergo noticeable seasonal changes. Seasonal differences are expressed mainly in the intensity and latitudinal position of the southern (subtropical) jets.
Due to the large temperature contrasts between low and high latitudes, the wind speed in the jet in the cold season is greater than in summer, and the maximum speeds are observed at lower levels. In the warm season, wind speeds are lower, and maximum speeds are observed at more high levels than in winter. Subtropical jet streams experience interseasonal shifts along the meridians. This can also be seen in the sections shown (Fig. 71 and 72).
In addition, in the subtropical jet stream system, the tropopause is always broken, and the jet axis is located between the tropical and extratropical (polar) tropopauses. On the contrary, in the zone of an extratropical jet stream, the tropopause is usually inclined, its rupture is observed in rare cases, and the axis of the jet is most often located under the tropopause. Therefore, in low latitudes, the zone of maximum wind speeds is usually higher than in middle and high latitudes. The rupture and slope of the tropopause are also expressed in the above vertical sections of the atmosphere.
Some data on the vertical and horizontal extent of tropospheric jet streams, as well as on the average maximum velocities in their system, can be found in Table. 27 and 28.
From Table. 27 it follows that the subtropical jet streams are relatively strong. Subtropical jets of large vertical and horizontal extent (within wind speeds of more than 100 km/h) are more common than the same extratropical jets.
In particular, subtropical jets with a width of more than 2000 km and a height of more than 12 km are much more common than extratropical ones. However, in some cases, extratropical jets are powerful, wind speeds in the center of the jet sometimes reach 400 km/h or more.
Most often, the average maximum speeds in the system of extratropical jet streams are 150–250 km/h, and in subtropical ones, 200–300 km/h. In other words, in terms of maximum velocities in the center, subtropical jets are on average more intense than extratropical ones (Table 28).
jet streams are relatively narrow zones of strong winds in the upper troposphere and lower stratosphere. The ST boundary is usually considered to be a wind speed of 30 m/s (100 km/h), a vertical wind shear of 5 to 10 m/s or more per 1 km altitude, and a horizontal wind shear of 10 m/s or more per 100 km. The jet stream resembles a strongly flattened pipe, which is 1-5 km high, 500-1000 km wide and thousands of kilometers long. Sometimes ST goes around the entire globe.
Jet streams are formed in the zones of convergence of warm and cold air masses, where significant pressure and temperature gradients are created, located between high-altitude cyclones and anticyclones.
Maximum speeds reach 350 km/h, over Japan up to 700 km/h. The ST intensity has a pronounced character. In cold weather, jet streams intensify, in summer they weaken.
Depending on the height of the location, there are tropospheric and stratospheric jet streams. Tropospheric STs occur when the surface of the main atmospheric front extends to the tropopause, and the temperature difference of the air masses lying on both sides of the front is 8-10° or more.
Tropospheric ST geographically divided into extratropical, subtropical and equatorial.
The jet streams of temperate latitudes associated with the polar front are extratropical, and the arctic ST is associated with the arctic front. Their predominant direction is west, and the intensity is subject to continuous changes. The axis of the extratropical ST is located at warm air, usually 1-2 km below the tropopause. It lies ahead of the surface line of the warm front at a distance of 400-500 km and behind the line of the cold front at a distance of 100-300 km. ST moves with atmospheric front.
The left side of the ST (in the direction of flow) is colder, located along the high-altitude region of low pressure, and is called cyclonic or cold. The right side is relatively warmer than the left, is located along the altitudinal region of high pressure and is called anticyclonic or warm. At the outer boundaries of the ST, due to the deceleration of the air flow by calmer air, large gradients (differences) in wind speed are observed. Its sharp changes cause the formation of turbulent zones. Such zones are more dangerous and intense on the left cyclonic side of the ST (under the action of two delay layers - the tropopause and the frontal surface). On the right, anticyclonic side, turbulent zones are less common, here turbulence is weak or moderate.
With respect to atmospheric fronts, the axis of the jet stream does not remain constant. In the wave stage, the ST axis is almost not curved and is located to the left of the front line; in the stage of a young cyclone, a bend is noted on the ST axis, while the ST axis is located to the left of the surface center of the cyclone. In the process of cyclone occlusion, the ST axis experiences an even greater bend, while the ST axis crosses the fronts much to the right of the surface front.
subtropical ST is formed on the northern periphery of subtropical anticyclones in winter between 25 and 35°N, and in summer between 35 and 45°N. In areas of great length (thousands of km), it has a stable western direction. Often in the cold half of the year, subtropical ST encircles the entire globe. The ST axis is located above the tropopause at an altitude of 12 km. The tropopause in the subtropical ST zone is ruptured. At a relatively short distance, the difference in its height during the transition of their cold to warm air can reach 4-5 km. The width of the subtropical ST is about 1500 km, the vertical extent is 8-12 km, compared to the extratropical ST, it is more stable and intense.
Equatorial ST are formed in equatorial regions on the southern periphery of high subtropical anticyclones and have an easterly direction.
Stratospheric MT - it is formed in winter at the latitude of the Arctic Circle and has a westerly direction, the axis is at an altitude of about 50 km, and the lower part covers the entire middle and upper atmosphere. average speed in this ST at altitudes of 20-25 km is about 200 km / h. The occurrence of this ST is explained by the presence of large temperature contrasts in the stratosphere at the boundary of the change of day and night. During the polar night (in January, the height of the night over the North Pole reaches 440 km), the stratospheric air in the Arctic cools down and turns out to be much colder than the stratospheric air south of the Arctic Circle. This results in large horizontal temperature gradients between temperate and arctic air.
Turbulence in the ST zone.
On the cold side of the ST, the horizontal wind shear is 12-14m/s for every 100km, on the warm side it is 10m/s. Vertical wind shear in ST is 5-10m/s per 1000m altitude, but can reach 25-30m/s. The presence of such gradients leads to turbulence in the ST region. The thickness of the disturbed layers is 300-600 mJ, sometimes increasing up to 1-3 km, the width usually does not exceed 100 km, and the length is several hundred kilometers. The magnitude of overloads during chattering does not exceed 0.5 - 1g, but sometimes there are cases up to 2g. In these cases, strong turbulence made it difficult to control the aircraft or led to more serious consequences.
Quite often, turbulence in the ST is observed in the area where Ci and Cc are located, which are formed on the right side of the ST, somewhat below its isi. To the left of the axis, clouds are formed less frequently; there are no clouds along the axis. The CT axis is the boundary between cloud systems on both sides of the CT.
Turbulent zones often occur in clear skies and are called TYN.
ST can be detected by changing the drift angle of the aircraft and changing the temperature. When the aircraft enters the left side of the ST, fast growth temperature (2-3° per 100 km of track) and left drift. At the entrance to the ST from the right side, the temperature drops (1-2° per 100 km of the way) and a right drift is observed. When flying along the ST, the air temperature does not change, but the ground speed increases (with a tailwind) or decreases (with a headwind).
When it enters the turbulence zone associated with the ST, they change the flight altitude by 300-400m or deviate from the route by 50-70km. It is recommended to change the flight altitude by decreasing if the flight takes place at altitudes of more than 8 km, and at lower altitudes - by going up. It is safest to deviate from the route to the right (anticyclonic) side of the jet stream.
During the pre-flight consultation, one should get acquainted with the map of maximum winds, with maps of baric topography and vertical sections of the atmosphere.
Weather maps and their analysis.
5.1 Weather maps. Ground and high-rise. Use of the international meteorological code KN-01. Analysis of Surface Maps.
The study of weather processes over a large area is most effectively carried out with the help of special maps, on which the results of simultaneous meteorological or aerological (high-altitude) observations are marked with conventional signs. Such maps are called synoptic (from the Greek word "synopticos" - simultaneously surveying).
A synoptic map on which observation data is plotted near the earth's surface is called a surface weather map, and a map with aerological observation data plotted is called a high-altitude or aerological map. A surface weather map is a meteorological map that reflects the actual state of the weather near the earth's surface at a specific point in time over a specific area. Weather maps are basic and ring.
The main charts are drawn at 0000, 0600, 1200 and 1800 hours Greenwich Mean Time (UTC). These maps cover vast territories and make it possible to analyze atmospheric processes over distances of several thousand kilometers.
On the AMSG, on the main maps, large-scale processes are predicted, such as the formation and movement of cyclones and anticyclones, the movement of atmospheric fronts. Using these maps, they make weather forecasts for a period of 24 ... 36 hours, as well as weather forecasts for long routes.
Ring cards (ring rings) are made every 3 hours: at 00.03, 06.09, 12.15, 18 and 21 GMT.
These are maps of relatively small areas - from several hundred
up to a thousand kilometers, using these maps they refine weather forecasts for several hours, and also draw up warnings about the occurrence of weather phenomena dangerous for aviation.
Weather information is applied to the main and ring maps in the form of numbers and conventional signs (symbols) in a strictly defined order around the circle of the station in accordance with the KN-01 code.
On the synoptic surface weather maps around the circle (point) of the station, the data are applied with code numbers and conventional signs.
TTTtT - air temperature, whole (TT) and tenths (tT) degrees Celsius;
TdTdtd - dew point, whole (TdTd) and tenths (td) degrees Celsius;
VV - horizontal visibility;
h(hh) - the height of the clouds of the lower tier;
Nh is the amount of lower clouds in oktas;
PPP - air pressure reduced to sea level, in hPa;
pp is the magnitude of the baric trend over the last three hours;
a - characteristic of the baric tendency;
N is the total number of clouds;
W is the weather between the periods of observation;
CL is the form of lower clouds;
CM is the shape of the middle tier clouds;
CH - form of clouds upper tier;
dd is the direction of the wind at the surface of the earth (where it blows from);
ff - wind speed is indicated by plumage;
ww - atmospheric weather phenomena since the observation period or during the last hour before the observation period;
Sn - sign negative value air temperature, dew point, pressure tendency.
The nature of the weather over any territory is determined by the properties of air masses, the position of atmospheric fronts, and the type of baric systems. The task of the analysis is to trace the movement of air masses, establish the nature of their stratification, identify pressure systems and determine the trajectories of their movement, as well as clarify the position and type of frontal sections. A complete spatial representation of atmospheric processes can be obtained using the entire complex of aerosynoptic material available at AMSG in the analysis.
Weather analysis usually begins with the analysis of surface synoptic maps - basic and ring, then maps of baric topography, upper-air diagrams, maps of maximum winds, tropopause maps and aviation maps of the AKP.
The analysis of surface weather maps begins with their "rise". The map highlights areas of heavy, drizzling and heavy precipitation, areas of cumulonimbus clouds and thunderstorm activity, areas occupied by fog, snowstorms, dust storms and other phenomena.
Then lines of equal values of baric tendencies are drawn. In the central part of the area of pressure growth, the letter P and the maximum pressure increase are marked in blue, in the central part of the drop, the letter P is written in red and the observed pressure drop. Lines of equal values of baric tendencies are called isallobars or isotrends. Then isobars are drawn - lines of equal pressures, the main forms of baric relief are revealed - cyclones, anticyclones, hollows, ridges, saddles. The centers of cyclones and anticyclones are denoted by the letters H and B, respectively.
All these stages are preparatory for the analysis of atmospheric fronts.
To analyze atmospheric fronts, their position is first studied using surface maps of previous periods, and then, based on the analysis of the baric field, wind fields, temperature, humidity, distribution of cloud systems, precipitation zones, and isallobaric regions, the position of the front and its type are determined. This takes into account all the factors that can lead to changes in weather conditions in the front zone, depending on the time of year and day, the nature of the distribution of pressure, temperature, etc.
The analysis of fronts is not limited to determining their position on a surface map, but maps of baric topography, aerological diagrams and other materials, such as satellite information, airborne weather, are used.
Baric topography maps are used in conjunction with surface maps, which allows a fairly complete analysis of weather processes and phenomena that are observed not only near the ground, but also at various altitudes.
For analysis, AT850, AT700, AT500, AT400, AT300, AT200 and AT100Hpa surface maps are used. For analysis temperature regime for the lower troposphere, OT500/1000 maps are used. The isohypses on this map are at the same time the isotherms of the average temperature of the lower 5-km troposphere layer. To clarify the position of atmospheric fronts, the AT850 map is used, on which frontal surfaces are detected better than on surface maps by temperature contrasts and other elements. To identify the location and characteristics of high-altitude frontal zones and associated jet streams, maps AT300, AT200, and less often AT500 are used.
According to these maps, the altitudinal frontal zone can be found in areas with the greatest concentration of isohypses and isotherms, where the strongest winds are observed, sometimes exceeding 100 km/h - a jet stream.
Typically, zones of intense turbulence are located in places of sharp divergence of air flows, especially if these zones are associated with the ST, and the front of the zone of divergence is located above the cold front.
When analyzing synoptic processes, an aerological diagram is used, from which some data can be obtained.
To predict the development of synoptic processes, the daily and annual variation of meteorological elements (daily variation of temperature, wind, negative temperatures in winter, high temperatures in summer) is taken into account. Taking into account the changes caused by the passage of atmospheric fronts, the development of cyclonic and anticyclonic formations. One of the stages is the prediction of the displacement of baric formations:
1. Cyclones move in the direction of the isobars of its warm sector, leaving warm air on the right;
2. The center of the cyclone moves parallel to the line connecting the center of pressure drop with the center of growth in the direction of fall.
If, in this case, negative tendencies are located only in the front part of the cyclone, not capturing its central part, and an increase of the same intensity is observed in the rear, then this indicates a rapid displacement of the cyclone.
If negative trends capture the center of the cyclone and the warm sector, this indicates its deepening, probable aggravation of fronts, an increase in cloud thickness and precipitation intensity.
3. If cyclones or anticyclones have a common closed isobar, then their centers rotate relative to each other for cyclones counterclockwise, for anticyclones - clockwise.
4. The trough moves with the cyclone to which it is connected and rotates counterclockwise around the cyclone.
5. The ridges move along with the anticyclone and rotate around the anticyclone in a clockwise direction.
When using baric topography maps for analysis, the following rules apply:
1. The surface centers of baric systems move in the direction of the air flow of currents (leading flow) observed in this moment above these centers, at altitudes of 3-6 km, i.e. in the direction of the isohypse on AT700 and AT500.
In this case, the speed of movement of the centers of surface baric formations will be 0.7 of the wind speed on AT700 and 0.5 of the wind speed on AT500.
2. High cyclones (AZn) with a vertical axis remain inactive and fill (collapse). A large tilt of the axis indicates a rapid movement of the baric formation.
3. Cyclones deepen if there is a divergence of flows above them on the AT700 and AT500 charts; are filled if there is a convergence of flows.
4. Anticyclones and ridges are strengthened if there is a convergence of flows above them on the AT700 and AT500 maps, and are destroyed if there is a divergence of flows.
To predict the movement of the front, the AT700 map is used, each point on the surface front line moves along isohypses passing over this point at a speed of 0.8 for warm and 0.9 for cold fronts from the wind speed on this isobaric surface.
Thus, by determining the speed and direction of movement of baric formations and atmospheric fronts, a forecast of the synoptic position is made, i.e. future location of atmospheric objects. Accounting for the evolution of atmospheric fronts and baric systems is an important element in the development of the synoptic position and weather forecast, and the weather forecast proceeds from the basic principle that with the movement of air masses and fronts, their inherent weather conditions are transferred with certain changes. Therefore, in the first approximation, those values of meteorological elements are taken, from which the front movement and air mass transfer are expected.
5.2 Maps of baric topography. Their analysis. tropopause maps.
Baric topography (BT) maps are compiled according to radio sounding data at 00, 12, UTC. These maps determine the meteorological conditions at various altitudes, and also refine the analysis of the weather near the surface of the earth. BT maps are made for surfaces of equal pressure, which are called isobaric.
Isobaric surfaces are not parallel to sea level. Depending on the distribution of pressure at sea level and on the distribution of air temperature, they either rise somewhat upward (above the anticyclone and in the area of heat) or fall down (above the cyclone and in the area of cold) relative to their average height. The height of the isobaric surface is expressed in geopotential meters 1 or decameters (tens of meters). There are an infinite number of isobaric surfaces in the atmosphere. In practice, several are usually distinguished, they are called standard, or main. Depending on the level of reference of the height of the isobaric surface, these maps are divided into maps of absolute topography (AT) - the height of the isobaric surface is measured from sea level and maps of relative topography (OT) - the height is measured from any lower isobaric surface or from the surface of the earth. In practice, they make up only one OT500/1000
1 The geopotential meter differs from the linear one by no more than 0.3%.
.
Isobaric surfaces and maps of baric topography
Absolute topography maps are compiled for the following isobaric surfaces:
850hPa, Nsr≈1.5km (layer 1…2km)
700 hPa, Nsr ≈ 3 km (2…4 km)
500 hPa, Nsr ≈ 5 km (4…6 km)
400 hPa, Nsr ≈ 7 km (6…8 km)
300 hPa, Nsr ≈ 9 km (8…10 km)
200 hPa, Nsr ≈ 12 km (10…12 km)
100 hPa, Nsr ≈ 16 km (12…14 km)
The following data is applied to AT cards:
Here HHH is the height of the isobaric surface, geopotential decameters (gp. dkm); t is the air temperature at the height of a given isobaric surface, °С; Δtd - dew point deficit, indicated by a number. The direction δ and ff is the wind speed and is plotted in the same way as on a surface map:
Points with the same height of a given isobaric surface are connected on AT maps by smooth black lines, which are called isohypses (isos - equal, gypsum - height).
After drawing isohypses on AT maps, the high-altitude centers of baric systems are distinguished. Altitude cyclones and anticyclones are outlined by closed isohypses. In a cyclone, the height of the isobaric surface to the center decreases, and in an anticyclone, the height of the isobaric surface to the center increases.
Using AT cards, the following parameters are determined.
1. Direction and speed of the wind in the area where there are no wind data, i.e. the direction and speed of the gradient wind, the characteristics of which depend on the direction and density of the isohypse.
2. Jet flow (ST). This is a wind current with a speed
100 km/h (30 m/s) and more, which extends for several thousand
kilometers horizontally. Sometimes ST encircles the entire globe.
The ST axis (maximum speed) is located 1.5 ... 2 km below
tropopause.
3. Cloudy and icing zones. On the isobaric surfaces of 850,700 and 500 hPa, cloudiness is likely at Δtd ≤ 2 °С;
on isobaric surfaces of 400, 300, and 200 hPa, cloudiness is likely at Δtd ≤ 4°С;
4. Chatter zones (_/\_ - moderate; -strong). If on a small section of the route there is a sharp change in the direction or speed of the wind, or both, then when flying on this section of the route, bumpiness will be observed;
5. Leading thread. This is the prevailing wind direction over the given region in the middle troposphere (in the 3-6 km layer). It is determined from the AT-700 and AT-500 maps. The leading flow determines the direction and speed of movement of the main baric systems, as well as the speed of movement of atmospheric fronts.
6. Vertical power of cyclones and anticyclones.
7. Position of atmospheric fronts and air masses.
8. Evolution of surface cyclones and anticyclones
tropopause maps.
Maps of the tropopause are made according to radio sounding data at 00 and 12 h GMT. They give an idea of the spatial position of the tropopause.
The following information is included on the cards:
Here PPP is the pressure at the lowest level of the tropopause; t is the air temperature at the tropopause level, °С; Δtd - dew point deficit, indicated by the code number (same as on AT cards).
The direction δ and the wind speed are plotted in the same way as on a surface map. The tropopause map for flights at high levels can determine where the aircraft will cross the tropopause and its inclination.
In places where the slope of the tropopause is equal to or greater than 1/300, strong turbulence will be observed. Crossing the tropopause in such areas is not recommended.
