Cyclostrophic Wind

For a PPL, CPL & ATPL aspirants who wants to become a good pilot, during flying prior to departure or enroute, earth atmosphere plays a vital role for safety of the aircraft.  To ensure this, pilot has to be well versant with earth atmosphere & other topics related to aviation meteorology.  At Gracious Avatar during commercial pilot training classes for PPL, CPL & ATPL aspirants, meteorology will be covered by the expert ground instructors.   Winds is one of the important topics which would be covered under meteorology subject during CPL & APTL pilot training at Gracious Avatar, Gurgaon (India).


Cyclostrophic Wind

1.    If the wind is blowing along curved isobars of radius r with a velocity V it has an acceleration towards the centre, called centripetal force (V2/r). The centripetal force(C) acting on a unit volume of air=ρV2/r. If the Coriolis force is negligible as compared to the forces P & C, then
ρV2/r=P  therefore V= (Pr/ ρ)1/2 . Such a motion is called cyclostrophic. Near the centre of a tropical revolving storm or in a circular tornado, the equation gives a good approximation to the actual wind.
2.    Cyclostrophic wind is defined as wind that blows as a result of balance between PG Force & Cyclostrophic Force.


Gradient Wind

It is the wind that blows parallel to the curved isobars under the balance of Pr Grad Force, Coriolis Force & Centripetal Force. In mid latitudes this wind is closer approximation than geostrophic wind.

Isallobaric Wind

When the pressure changes rapidly, the geostrophic and gradient rules do not apply. In such a case another force called isallobaric force comes into play. This force is directed from higher isallobar to lower isallobar. This deflects the wind towards the falling pressure. The wind under the influence of P, f and isallobaric force is called the Isallobaric wind.

Effect of Surface Friction

The rough terrain causes friction. Depending upon wind speed, lapse rate and roughness of the surface, effect of friction may extend to about 1 km. This layer is called friction layer. Thickness of the layer is variable. Within the friction layer wind slows down and the Coriolis force reduces proportionately and is insufficient to balance Pressure Gradient Force. The wind is therefore, deflected towards the low pressure and the flow become cross isobaric.

As a rough rule, over sea where friction is small, surface wind blows at about 15o to isobars. Over land it is 30o to the isobars with its speed about 1/3 to 1/2 of geostrophic value.

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Why ATMOSPHERIC OBSCURITY Important in Commercial Pilot training

For a PPL, CPL & ATPL aspirants who wants to become a good pilot, during flying prior to departure or enroute, earth atmosphere plays a vital role for safety of the aircraft.  To ensure this, pilot has to be well versant with earth atmosphere & other topics related to aviation meteorology.  At Gracious Avatar during commercial pilot training classes for PPL, CPL & ATPL aspirants, meteorology will be covered by the expert ground instructors.   Atmospheric Obscurity is one of the important topics which would be covered during CPL & APTL pilot training at Gracious Avatar, Gurgaon (India).




Visibility in pure air should be infinite. However, air is never pure and is laden with dust, smoke, industrial pollutants, aerosols etc. Presence of these suspended obscurities reduces the visibility.

Horizontal Visibility

Horizontal Visibility is the maximum distance along the horizontal up to which prominent objects can be seen with the naked eye and are recognized as such under natural light. Visibility may be different in different directions. The visibility reported by Met Office is the lowest Horizontal Visibility. During day Visibility is estimated by seeing objects at pre-measured distances, within and around the airfield. During night existing lights in and around the airfield at known distances are used. These are called Visibility Land Marks.

Runway Visual Range (RVR)

It is the distance up to which the pilot can see from the cockpit along the runway. RVR is reported when the visibility is less than 1500m. RVR is reported in multiples of 25M when between 50M & 150M, in multiples of 50M when between 150 & 800M, in multiples of 100M when between 800 & 1200M, and in multiples of 200M when more than 1200M.


PoorVisibility Phenomena

1.    Haze: Atmospheric obscurity due to very small particles of smoke, dust, water etc., wherein the visibility reduces to 5000M or less (but more than 2000M) is termed as haze. When the Relative Humidity is 75% or more, this is termed as Moist Haze(or simply Haze) whilst if the RH is less than 75% it is termed as Dust Haze or smoke Haze.It gives a milky appearance to the sky.
2.    Dust Haze: Atmospheric obscurity due to dust particles in suspension with RH less than 75% reducing visibility to 500oM or less is termed as Dust haze. It is caused by the strong winds in the desert or arid areas arising due to a steep pressure gradient kicking up dust in the stable lower layers of the atmosphere.
3.       Smoke Haze: Atmospheric Obscurity due to suspended smoke from industrial or domestic sources reducing visibility to 5000M or less is termed as Smoke haze. Smoke Haze occurs when wind is calm and there is strong ground inversion.
4.    Mist: Atmospheric obscurity due to suspended droplets wherein visibility reduces to 1000 M to less than 2000 M, with RH being 75% or more.
5.    Fog: Atmospheric obscurity due minute water droplets suspended in the air reducing visibility to less than 1000M.In Fog RH is nearly 100%. Fog may be termed as thick, moderate or light depending upon visibility.
6.    Smog: When smoke haze & fog co-exist, it is called Smog. In smoke visibility is very poor.
7.    Dust Storm: The visibility in dust storm is 5000M or less. If the dust storm is followed by rain visibility improves fast.    
8.    Precipitation: The visibility in precipitation depends on the size of the drop and intensity of precipitation. In moderate Rain vis may reduce to 1-3 km, in heavy Rain or showers to less than 1000M, in drizzle to 3 km and in snowfall it may reduce to less than 1000M.

Horizontal, Vertical & Slant Visibility

1.    Visibility reported by Met Office is minimum horizontal vis.
2.    Vertical visibility may be much better during shallow fog as it is the distance up to which one can see objects along the vertical.
3.    Slant visibility is the visibility at an angle and can be defined as the distance an object can be seen along the path that is at an an angle to the horizontal( usually glide path or landing path).In shallow fog this visibility is more than horizontal vis but less than vertical vis.


Instrumentsfor Measuring Visibility

1.    Scopograph or transmissometer are used for measuring vis along the different runways on an aerodrome. RVR equipment are installed along various runways to measure RVR.
2.    Close to take off & landing areas.
3.    The equipment consists of a light source and a photo-electric receiver, which generates electric current according to the obscurities present between the transmitter and receiver. The current so generated gives a measure of RVR. The display units are installed in Met Office and ATC Tower.


1.    Fog is composed of tiny water drops or ice crystals. It is nothing but a stratus cloud sitting smack on the ground. Fog occurs due to condensation of water vapour present in the layers of air close to the ground. Condensation can occur either by cooling of the air close to the ground or by feeding moisture in to the air to saturate it. Fog can be various types:
2.    Radiation Fog: Radiation Fog forms due to nocturnal cooling of the ground and the adjacent layers. The conditions favorable for formation of Radiation Fog are: a.    Clear skies b.    High relative Humidity e.g. after Rain c.    Light  freshening wind  of 3 to 8 kt 3.       Radiation fog is most frequent at about sunrise and dissipates within 2-3 hours after sunrise due to heating. If the Fog is thick it may take longer to lift. Generally fog lifts in to low stratus clouds before dissipating. Radiation Fog in India occurs mostly during winters after the passage of active western disturbances. It is almost a daily feature in winter season in the Valley of Brahmaputra River where adequate moisture is present and katabatic flow provides the required degree of turbulence and extra cooling. The most susceptible areas for radiation fog are NW India, UP, Bihar, Bengal and Assam (particularly south of Brahmaputra River).
4.    Vertically radiation Fog extends to only a few hundred feet whilst sometimes it can extend up to about 1500ft.
5.    Advection Fog: Advection Fog forms when warm moist air from elsewhere is transported over the cold surface (ground or water) where the surface temperature is less than the dew point of the advected air. Advection Fog forms both over land & sea. Coastal fogs over Bengal and Orissa during winters are due to a combined effect of advection from sea and radiation cooling. The Brahmaputra valley, the coastal areas and hills of Indian Peninsula experience advection Fog.
6.    Frontal Fog: Frontal Fog forms near the front due to saturation of air in the area of continuous rain ahead of the front. It also forms due to lowering of the cloud to the surface with the passage of a front.
7.    Steaming Fog: This type of Fog is common in higher latitudes when cold air mass flows over a warm sea surface. The water vapour from warm sea when comes in contact with the cold air aloft condenses to form steaming fog. It is common over frozen land, ice covered Polar Regions and over Icelandic and Norwegian regions. Over sea it is often referred to as sea smoke. It looks like steam coming out of the surface.

Fog Dispersal:

1.    Thermal Dispersion: When air is heated to temperatures above dew point, fog or cloud will dissipate.
2.    Dispersal using Hygroscopic Nuclei: When hygroscopic particles are injected into fog water drops form. This lowers the relative humidity of the air and fog dissipates.
For More Info :-

How Do I Become a Pilot

For a PPL, CPL & ATPL aspirants who wants to become a good pilot, during flying prior to departure or enroute, earth atmosphere plays a vital role for safety of the aircraft.  To ensure this, pilot has to be well versant with earth atmosphere & other topics related to aviation meteorology.  At Gracious Avatar during commercial pilot training classes for PPL, CPL & ATPL aspirants, meteorology will be covered by the expert ground instructors.   Humidity is one of the important topics which would be covered during CPL pilot training.


  1. Water vapor is always present in the air to a greater or lesser extent, in the troposphere.
  • Water evaporates into the air from oceans, lakes, vegetation etc. It ascends and forms clouds which cause precipitation.
  • Water exists in three phases: the gas (water vapor), liquid (rain, drizzle, shower) and solid(snow, hail).
  • The capacity of air to hold water vapor depends largely on temperature and to some extent on pressure. Higher the temperature, higher is the capacity of air to hold water vapor.
  • Dry Air: Air that contains no water vapor. Exists in upper troposphere or stratosphere.
  • Moist Air: The normal air that we breathe. It is also called unsaturated air.
  • Saturated Air: When air holds maximum water vapor, it is called saturated air.
  • Vapor Pressure: The partial pressure exerted by water vapor in the air. If p is the total pressure of air and e is the vapor pressure, then p-e is the pressure of dry air.
  • Saturated Vapor Pressure: It is the pressure exerted by water vapor when air is saturated.
  1. Absolute Humidity: It is the actual amount of water vapor contained in a given volume of air at a given temperature. It is expressed as g/m3.
  1. Humidity Mixing Ratio: It is defined as the mass of water vapor contained in a given mass of air. It is expressed as g/kg.
  1. Humidity Mixing Ratio for Saturated Air: It is defined as the maximum mass of water vapor that can be contained in a given mass of air at a particular temp and pressure. It is expressed as g/kg.
  1. Relative Humidity: It is defined as the ratio, in percentage, of the actual water vapor present in the air to the maximum it can hold at the same temperature and pressure.
  1. RH= HMRx100/HMR for saturated air.
  1. RH=Vapor pressure of Airx100/Saturation vapour pressure of Air.
  1. Wet Bulb Temperature (Tw Tw): It is the lowest temperature which air would attain by evaporating water into it to saturate it. Desert Coolers work on this principle.
  1. Dew Point Temperature (Td Td): It is the lowest temperature to which air should be cooled at constant pressure to saturate it with respect to water. Cooling below dew point causes condensation.
  1. Frost Point: It is the temperature to which air must be cooled to reach saturation with respect to ice. Cooling below the frost point causes formation of hoar frost.

Important Points

  1. As the temperature of the air increases, the amount of water vapour required to saturate it also increases.
  • At subzero temperatures water molecules have more energy and greater degree of freedom than ice, consequently the saturation vapour pressure over water drops is more than that over ice particles.
  • If water drops and ice particles co-exist, water drops will evaporate and condense on the ice particles. This explains rainfall from clouds which extend above 0oC and have both super cooled water drops and ice crystals co-existing.
  • Small water drops can exist in super cooled state up to -40o C.
  • For saturated Air( in Fog, Rain ) Air Temp(TT)=TwTw=TdTd
  • For unsaturated air: Dry Bulb Temp>Wet Bulb Temp>Dew Point

For more info :-

How to TEMPERATURE Effect in Commercial Pilot Training

For a PPL, CPL & ATPL aspirants who wants to become a good pilot, during flying prior to departure or enroute, earth atmosphere plays a vital role for safety of the aircraft. To ensure this, pilot has to be well versant with earth atmosphere & other topics related to aviation meteorology. At Gracious Avatar during commercial pilot training classes for PPL, CPL & ATPL aspirants, meteorology will be covered by the expert ground instructors. Temperature is one of the important topics which would be covered during CPL pilot training.


  1. Temperature is a measure of heat.
  • It is measured by means of thermometer in degrees Celsius or Fahrenheit. These scales are arbitrarily fixed with reference to the melting point of ice and the boiling point of pure water at normal pressure. On the Celsius scale these are respectively as 0⁰ C and 100⁰ C and in Fahrenheit scale as 32⁰ F and 212⁰ F. Celsius scale is used internationally, in aviation and science. Use of Fahrenheit scale is confined to English- speaking countries only.
  • Heat is a form of energy. As heat is extracted from a substance, its internal energy is reduced and the random motion of its molecules slows down. The molecules get arranged in a more orderly pattern than before. As more heat is extracted the cooling and orderliness increases. Finally a state is reached when no more heat can be extracted and the molecules reach their maximum orderliness and the molecular motion almost ceases. The lowest temperature is reached. This minimum temperature is the same for all substances, and is accordingly called the absolute zero (K). 1K=-273.16 ⁰ C.

Conversion to C, F & K

  1. F= 9C/5 + 32
  2. C= 5/9 (F-32)
  3. K= C+ 273
  4. Note that -40 ⁰ C = -40 ⁰ F


Instruments for Measurement

  1. Dry Bulb Thermometer, Wet Bulb Thermometer (the bulb is covered with a muslin cloth which is kept moist), Maximum Thermometer (like doctors Thermometer), Minimum Thermometer and Thermograph, are used for measuring temperature.
  • Mercury is used in thermometers except in Minimum Thermometer in which alcohol is used instead of mercury.
  • In Thermographs and in Upper Air temperature measurement, bi- metallic strips are used.
  • A minimum thermometer has dumbbell shaped iron index, which permits alcohol to pass through it when the temperature rises. When temperature falls the alcohol, which has a conclave meniscus, drags the index back to indicate minimum temperature.
  • Surface temperature is recorded at a height of 4 ft(1.25m) from the ground in shade(inside a Stevenson’s Screen).

Dry Air & Moist Air

  1. Air which has no water vapour content is called dry air. Such air may exist at very high levels. For all practical purposes unsaturated air is called dry air.
  • With water vapour <4 % (RH <100%) air is called unsaturated or dry.
  • With water vapour >4 %(RH 100%) air is called saturated air.


Heat & Temperature

  1. Specific Heat: It is defined as the heat required to raise the temperature of unit mass of a substance by 1⁰C. The specific heat of water, regarded as the highest is 1, that of ice 0.5 and of soil 0.2.
  • Latent Heat: It is defined as the amount of heat absorbed or released during change of phase from/to solid/liquid/vapour. It is absorbed during change from solid to liquid and liquid to gas and released during change of phase from vapour to liquid and liquid to solid.
  • When water changes to vapour, a certain quantity of heat is supplied. To change boiling water into vapour, more than five times as much heat is required as is needed to bring the temperature of ice cold water to a boil. Once the boiling begins, the temperature remains constant and the heat released is stored as latent heat. It is released as latent heat when the water vapour condenses to water.

Heat Transfer Processes

  1. Heat is transferred from one place to the other by conduction, convection and radiation.
  • Conduction: In this Process heat is physically transferred by the molecules by contact. Conduction is important process of heat transfer very close to the ground.
  • Convection: In this process heat is bodily transferred to the colder part of the fluid. As more than 70% of the earth is covered with water, hence the importance of convection.  In the atmosphere free Convection is triggered by intense solar heating and the forced Convection by topography.
  • Radiation: Everybody radiates heat at its temperature. In this process of heat transfer the medium is neither affected nor required. The solar radiation directly heats up the earth without affecting the atmosphere.
  • Other Methods: Advection, Latent Heat release, Turbulence, Up and downward motion of air are the other methods of heat transfer.

Diurnal Variation of Surface Temperature

  1. Diurnal variation of temperature is more over land areas than over sea/coastal areas.
  • Sea Surface temperature shows an average variation from day to night of less than 1⁰C, whereas over land the variation may average as much as 20⁰C.
  • Variation is max when wind is calm.
  • Due to nocturnal cooling the surface temperature continues to fall even after sunrise till a balance is reached between the incoming and outgoing radiation. The balance occurs a little after sunrise.
  • Cloud cover can hamper both cooling and heating.
  • Cloudy nights are warmer than clear nights
  • Cloudy days are less warm than clear days.

For more info :-

Aptl Integrated Course

For a PPL, CPL & ATPL aspirants who wants to become a good pilot, during flying prior to departure or enroute, earth atmosphere plays a vital role for safety of the aircraft.  To ensure this, pilot has to be well versant with earth atmosphere & other topics related to aviation meteorology.  At Gracious Avatar during commercial pilot training classes for PPL, CPL & ATPL aspirants, meteorology will be covered by the expert ground instructors.   Pressure is one of the important topic which has to be covered during commercial pilot training.



Static & Dynamic Pressure

1.      When the air is at rest its molecules are in random motion all over. The pressure exerted by these molecules is uniform in all directions. This Pressure is called Static Pressure or Barometric Pressure.
2.      If the air is in motion an additional pressure is exerted in the direction opposite to the flow. This is called Dynamic Pressure or Wind Pressure. Wind pressure is used in the design of air speed indicator.

Pressure as Weight of the Air Column

1.      The atmospheric Pressure at any level is the weight of the column of air of unit cross-section extending vertically upwards to the top of atmosphere.
2.         As the weight decreases with height, the pressure also decreases with height.
3.         ICAO has adopted hector Pascal (hPa) as the unit of atmospheric pressure. The other units are mm, and inches.



  Relationship between Pressure & Altitude

1.      Roughly 1 hPa change in Pressure is equivalent to :

at MSL 27 ft
at 20000 ft 30 ft
at 30000 ft 50 ft
at 40000 ft 100 ft

2.      The pressure decreases with height from sea level to 600m at 4%, up to 1.5 km at 3% and up to 3.0 km at 2.5%. At 6 km it reduces to half the value at sea level and is negligible at 100 km.

Variation of Pressure in Warm & Cold Air

1.    Warm Air is less dense than the Cold Air.
2.    Pressure falls at a faster rate over a cold column of air than a warm column of air.
3.    Where upper Air Mean Temperatures are higher upper Air Mean Pressures are higher and where mean Temps are lower mean pressures are lower.

Diurnal Variation of Pressure

1.    Atmospheric Pressure follows a wavy pattern during 24 hours, showing maxima at 1000h & 2200h and minima at 0400h & 1600h local time. Such variations are very small at poles and large at equator.
2.    When the temperature is highest in the afternoon, the density of air close to the ground is low. Hence the pressure is lowest. At about sunrise when the temperature is lowest, the pressure is highest. There is a phase difference of about 3 hours between the temperature and the pressure.
3.    Diurnal variation of pressure is probably a natural oscillation of the atmosphere, having a period of almost 12 hours.
4.    As the air is continuous, if there is a high pressure at one place there has to be a low pressure on the opposite side of the globe. With the rotation of the earth the pressures also rotates. Hence, two maxima and two minima in 24 hours.



Pressure Systems

1.    Low (Cyclone): It is an area enclosed by an isobar with lowest pressure at the centre. When there are two or more closed isobars at an interval of 2 hPa, it is called a Depression. Winds around a low blow in anticlockwise direction in N hemisphere converging towards the centre. There is convergence and upward motion at a low. Hence it is associated with bad weather.
2.    Trough of Low: A tongue like extension of isobars from a low is called trough of low. Pressure along the trough is lower than on either side. Isobars along the trough are V- shaped and wind direction abruptly changes and backs.
3.    High: It is a region enclosed by isobars with highest pressure at the centre. Wind in a high moves in a clockwise direction. It is associated with fair weather but visibility is poor due to subsidence.
4.    Ridge: It is a wedge like extension of isobars from a high pressure area. Pressure is higher along the ridge than on either side.


Height Vs Pressure

Sea Level 1013 hPa
10000 ft 700 hPa
18000 ft 500 hPa
24000 ft 400 hPa
30000 ft 300 hPa
34000 ft 250 hPa
38000 ft 200 hPa
44000 ft 150 hPa
53000 ft 100 hPa

QFE: Pressure measured at the airfield setting point.
QNH: Pressure reduced to mean sea level using ISA specifications.
QNE: 1013 set on altimeter sub scale, will, on landing give an altitude known as the QNE value.
QFF: Pressure reduced to mean sea level using standard met practices (temperature at the station, which is isothermal lapse rate).
For more info :-


For a PPL, CPL & ATPL aspirants who wants to become a good pilot, during flying prior to departure or enroute, earth atmosphere plays a vital role for safety of the aircraft.  To ensure this, pilot has to be well versant with earth atmosphere & other topics related to aviation meteorology.  At Gracious Avatar during ground classes for PPL, CPL & ATPL aspirants, meteorology will be covered by the expert ground instructors.   
The atmosphere of the earth is an envelope of air around earth and it is bound to the earth due to the gravitational pull of the earth. Effectively, it is part of earth and moves with the earth as the earth rotates on its axis. Air is a mixture of gases, and this mixture is quite homogeneous upto about 80km due to turbulent flow, whilst above 80 km the atmosphere is heterogeneous.
Composition & Characteristics
1.         Since atmosphere is made up of air and air has weight, so the atmosphere has weight and it exerts pressure. Atmosphere has no definite shape. It occupies space. Air is a mixture of gases- the most prominent being Nitrogen and Oxygen. The ratio of gases present in the air is :- Nitrogen 78.08%, Oxygen 20.95%, CO2 0.035%, Argon (A2) 0.03% and traces of Helium, Methane, Hydrogen, Nitrous Oxide, Ozone, Xenon etc.
2.         Nitrogen And Oxygen making up most of the atmosphere can be said to have a ratio which is :- Nitrogen: Oxygen= 3:1 (By Weight) Nitrogen: Oxygen= 4:1 (By Volume)
3.         Even though atmosphere is quite homogeneous, it shows remarkable variable quantities of water vapour in the lower troposphere and of ozone in the lower stratosphere (20-25km). 4.         Water vapour, Carbon dioxide and Ozone, though present in small quantities have significant effect on weather and life. These gases are called Green House Gases. Ozone in the stratosphere absorbs harmful ultra-violet radiation from the sun and protects us. 5.         Air which has no water vapour is called dry air. A mixture of Dry air and water vapour is called Moist Air. The air which has >4% water vapour (=100% RH) is called saturated. Similarly, the air which has <4% water vapour (RH<100%) is called unsaturated. In meteorology, all air that is unsaturated is called Dry Air.

Vertical Distribution of Air

Due to the gravitational attraction of the earth, most of the atmospheric mass is concentrated in the lower portion and the density decreases rapidly with height. As a rough estimate :-         ·         1/2 of the atmospheric mass is contained in the lower 6 km ·         3/4 of the atmospheric mass is contained in the lower 10 km ·         99% of the atmospheric mass is contained in the lower 35 km

Thermal Structure of the Atmosphere

1.    Sun is the main source of energy for the earth. It gets heated up by the sun’s rays during day and then heats the layers above by conduction, convection, radiation and latent heat.
2.    Sensible Heat (Conduction, Convection & Radiation) – 23%.
3.    Latent Heat (Evaporation, Condensation & Sublimation) 77%.
4.    Due to absorption of solar radiation the atmospheric layers close to ground are warmer than layers above.
5.    The temperature falls with height. This trend however does not continue till the end of atmosphere.
6.    Based on temperature distribution the atmosphere is divided into layers viz. troposphere, stratosphere, mesosphere & Thermosphere (which includes ionosphere).
7.    The top of the troposphere where the temperature stops falling is called tropopause. It is a boundary layer between troposphere & stratosphere.
8.    Higher the temperature at surface higher will be tropopause.
9.    Above (not at) 8km there is a reversal of temperature & density and above this height poles are warmer than equator.


1.    Lowest layer of atmosphere is troposphere. 2.    Extends to 16-18 km over equator and 8-10 km over poles. 3.    Temperature falls with height at a uniform rate of 6° C/km. 4.    In day to day conditions temp may fall (lapse), rise (inversion) or stay constant (isothermal).Troposphere is generally unstable and thus most weather occurs in this layer. 5.    70% of the atmosphere lies within this layer. 6.    Tropopause is top of troposphere and a boundary between troposphere and stratosphere. 7.    At tropopause the temperature stops falling with height. Lapse rate, if any, reduces to just 1-2°/km. 8.    Height of tropopause is 16-18 km over equator and 8-10 km over poles. 9.    There are breaks in Tropopause where jet stream occurs.
10. Polar tropopause- Pole ward of 45-600 N 300 hPa. 11. Tropical tropopause- Equator to 350 N 100 hPa. 12. Jet Stream at 200 hPa between the two tropopause.


1.    The layer above troposphere which is much stable and in which temperature rises with height is stratosphere. 2.    Nacreous clouds or mother of pearl clouds are seen in upper stratosphere in higher latitudes. 3.    The temperature in lower stratosphere slowly decreases with height in high latitudes in winters, remains nearly constant in the mid-latitudes and increases with height in lower latitudes. 4.    In the upper stratosphere (above 30 km) there is general increase of temperature with height due to absorption of UV rays by Ozone and Oxygen.
5.    The top of stratosphere where once again the temperature has stopped rising and has reached about 0° C is called Stratopause. It occurs at a height of 50 km.


1.    Mesosphere extends from Stratopause to about 80 km. Lack of absorption of solar radiation and weak vertical mixing causes temperatures to fall with height in this layer.
2.    On rare occasions Noctilucent clouds are seen in upper Mesosphere.
3.    The level at the top of Mesosphere where temperatures after reaching about -90° C stop falling is called Mesopause. It generally occurs at about 80 km.


1.    The region extends from Mesopause to the outermost fringes of the atmosphere in which temperature increases with height up to 200 km.
2.    In this layer air is very thin and very few molecules are present. However, there are ionized particles that move rapidly and strike each other thus increasing temperature.
3.    The temperatures are about 600° C at 200 km which increases to 2000° C during sunspot maxima.

International Standard Atmosphere
ISA has been defined by ICAO. Its specifications are:-
1.    Air is Dry.
2.    Temp at MSL 15°C.
3.    Pressure at MSL 1013.25 hPa.
4.    Acceleration due to gravity 980.665 cm/sec2.
5.    Lapse rate up to 11km 6.5° C/km.
6.    Temp assumed constant at -56.5° C from 11km to 20 km.
7.    From 20 to 30 km there is a rise of temp at the rate of 1° C/km with a temp of -44.5° C at 32 km.

 For more info :-

What Is Airborne Weather Radar?

It is very interesting to know that nowadays majority of aircraft’s fly a high altitude. But there are lots of clouding too, in such high altitudes. So, how the aircraft manages to avoid or penetrate such clouds. Here it is how.

Nowadays almost all the commercial aircraft are fitted with Airborne Weather Radar system.

It is basically a Primary Radar whose antenna is fitted on the nose of aircraft and scans the forward area ahead of aircraft track.

Weather Radar transmits pulses which are reflected by the water droplets which are present on the clouds. The denser the cloud, more will be the content of water droplets and hence more of the transmitted pulses will be reflected back to the aircraft and the intensity of reflected pulses will be displayed accordingly.

You will study further in details during CPL & ATPL training modules.

For more info :-

What Is Navigation

Finding the way from one place to another is called NAVIGATION.

Aircraft Navigation is the art and science of getting from a departure point to a destination in the least possible time without losing your way.

In the past, plotting on the paper or on the map a course towards a specific area of the earth used to be a task assigned to a specialized member of the aircraft’s crew such a navigator. Such a task was quite complicated and not always accurate. Since it depended on the observation, using simple maps and geometrical instruments for calculations.

Today, aerial navigation has become an art which nears to perfection. Both external Navaids (Navigational Aids) and on-board systems help navigate any aircraft over thousands of miles with such accuracy that could only be imagined a few decades ago.

Pilots have various navigation aids that help them take-off, fly, and land safely.

One of the most important aids is a series of air route traffic control, operated throughout the world.

Most of the traffic control uses a radar screen to make sure all the planes in its vicinity are flying in their assigned airways.

Airliners carry a special type of radar receiver and transmitter called a transponder.

It receives a radar signal from control center and immediately bounces it back.

When the signal got to the ground, it makes the plane show up on the radar screen.

There are various navigational aid equipment and system which you will study further in details during pilot training modules.

For more info :-

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