The friction layer is a layer of air on the earth’s surface 2000 to 3000 ft (1 km) thick where the horizontal flow of air is disturbed by both thermal and mechanical turbulence.

caused by physical obstructions to the normal flow of air such as hills, mountains, coasts, trees and buildings.

Vertical windshear is change in wind velocity with height. It is typically measured in knots per 100ft. This type of windshear is very common during an inversion, therefore expect them at night and in well developed high pressure systems such as those found under the sub tropical high pressure belt. As an aeroplane fly’s through an inversion, not only will the change of temperature cause the engine performance to change, but the abrupt change in wind speed and direction may significantly alter the flight path.

Altocumulus lenticularis, also known as lenticular cloud, is found downwind of mountainous or hilly areas, and is indicative of the presence of mountain wave activity. Because of its position downwind of high ground, moderate or even severe turbulence may be found beneath altocumulus lenticularis. However, the air in the lenticular clouds, themselves, is always smooth.

Vertical windshear is change in wind velocity with height. It is typically measured in knots per 100ft. This type of windshear is very common during an inversion, therefore expect them at night and in well developed high pressure systems such as those found under the sub tropical high pressure belt. As an aeroplane fly’s through an inversion, not only will the change of temperature cause the engine performance to change, but the abrupt change in wind speed and direction may significantly alter the flight path.

Vertical windshear is change in wind velocity with height. It is typically measured in knots per 100ft. This type of windshear is very common during an inversion, therefore expect them at night and in well developed high pressure systems such as those found under the sub tropical high pressure belt. As an aeroplane fly’s through an inversion, not only will the change of temperature cause the engine performance to change, but the abrupt change in wind speed and direction may significantly alter the flight path.

Vertical windshear is change in  horizontal wind velocity with height. It is typically measured in knots per 100ft.

Horizontal windshear is change in wind velocity with horizontal distance and is common with the passage of fronts

Clear air turbulence (CAT). occurs around the boundaries of jet streams because of the large horizontal and vertical windshears.

Change flight level if you encounter cat

Clear air turbulence (CAT). occurs around the boundaries of jet streams because of the large horizontal and vertical windshears. It is strongest near to, or just below, the jet axis on the cold air (low pressure) side with a secondary area above the axis

During early afternoon low pressure areas form over land masses due to solar heating,

Vertical windshear is change in wind velocity with height

wind velocity is represented in Kt.

height in feet

Altocumulus lenticularis, also known as lenticular cloud, is found downwind of mountainous or hilly areas, and is indicative of the presence of mountain wave activity. Because of its position downwind of high ground, moderate or even severe turbulence may be found beneath altocumulus lenticularis. However, the air in the lenticular clouds, themselves, is always smooth.

Decreasing the speed will give more allowance for the thrust and we can climb faster

CONDITIONS NECESSARY FOR FORMATION OF STANDING WAVES (MOUNTAIN WAVE)

 Windspeed at mountain height must be at least 15 kt (often more than 20 kt is required) increasing with height.

 The wind must blow within 30 degrees of the perpendicular to the range of hills/moun-tains.

 There must be a region of marked stability such as an inversion or isothermal layer at mountain top height with less stable air above and below.

Jet streams are narrow bands of fast moving air commonly found beneath the tropopause. These air currents can be very fast, especially over South East Asia in winter where the highest recorded velocity was 407 kt. Around these fast currents of air are eddies and shear lines, just like around the edge of powerful river. The shear lines are created when there is marked change in wind speed and direction. This is commonly called Wind shear and is creates very dangerous Clear Air Turbulence (CAT).

Turbulence in jet streams is most severe:
 With stronger winds.
 With curved jet streams.

Seasonal and Diurnal Variation
The atmosphere becomes stable at lower levels after sunset due to radiational cooling. At the same time the winds also weaken in the lower layers. This results in the formation of waves, on the lee side of small and medium height mountains, called evening waves. These waves continue throughout, till the warming up after sunrise destroys the stability structure. In the case of large mountains, however, this effect is negligible.
In winters the winds are steady and strengthen with height and the atmosphere has suitable stability. Hence the mountain waves are more frequent in the winters.

in summers in the morning mountain waves are not frequent, hence Vfr should be conducted

Vertical windshear is change in wind velocity with height. It is typically measured in knots per 100ft. This type of windshear is very common during an inversion, therefore expect them at night and in well developed high pressure systems such as those found under the sub tropical high pressure belt

Thunderstorms

If the downdraught descends from beneath a cumulonimbus or cumulus congestus, it may come into contact with the ground, and then spread out, from the cloud itself, sometimes up to distances from the cloud of 15 – 20 miles. This type of phenomenon causes large changes in the direction and speed of the wind in the vicinity of the cloud, both vertically and horizontally, and may, thus, give rise to dangerous low level wind shear.

Clear air turbulence (CAT). occurs around the boundaries of jet streams because of the large horizontal and vertical windshears.

Altocumulus lenticularis, also known as lenticular cloud, is found downwind of mountainous or hilly areas, and is indicative of the presence of mountain wave activity. Because of its position downwind of high ground, moderate or even severe turbulence may be found beneath altocumulus lenticularis. However, the air in the lenticular clouds, themselves, is always smooth.

virga are trails of precipitation that fall from the underside of a cloud but evaporate or sublime before it can reach the earth’s surface

Altocumulus lenticularis, also known as lenticular cloud, is found downwind of mountainous or hilly areas, and is indicative of the presence of mountain wave activity. Because of its position downwind of high ground, moderate or even severe turbulence may be found beneath altocumulus lenticularis. However, the air in the lenticular clouds, themselves, is always smooth.

As an aeroplane fly’s through an inversion, not only will the change of temperature cause the engine performance to change, but the abrupt change in wind speed and direction may significantly alter the flight path.

Altocumulus lenticularis, also known as lenticular cloud, is found downwind of mountainous or hilly areas, and is indicative of the presence of mountain wave activity. Because of its position downwind of high ground, moderate or even severe turbulence may be found beneath altocumulus lenticularis. However, the air in the lenticular clouds, themselves, is always smooth.

Inversion layer is reported just after take of, winds will change abruptly after take off, resulting in lower climb and possible windhear, we should take opposite of the wind being reported as after take off immediate change of wind direction are expected