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. Study Kwik eLearning module helps the PPL, CPL & ATPL aspirants, to go through the winds chapter in detail which is one of the important aspect of aviation flying.
In the atmosphere air moves horizontally and vertically. The horizontal movement of air is called WIND. It has two components- direction and speed.
The direction of the wind is the direction from which wind is blowing or coming from. A southerly wind blows from south to north, Easterly wind blows from east to west & southwesterly wind blows from southwest to north east. Wind directions are indicated on 16 points of compass. It is also expressed in degrees at an interval of 10o e.g. 330o/15kt; 280o/40kt etc.
1. It is expressed in terms of nautical miles per hour (knot). It can also be expressed in terms of meters per second (mps) and km per hour (kmh).
3. 1kt=0.5 mps=2kph.
4. Wind speed is reported at an interval of 5 kt as follows:
• 0-2 kt as calm
• 03-07 kt as 5kt
• 08-12 kt as 10 kt —– and so on.
Runways are oriented along the most prevalent wind directions of a locality, based on climatological records. However, sometimes, especially during adverse weather and transition seasons, the winds deviate from these directions. A wind 90o to the runway in use is called cross wind component. Critical cross wind component for each aircraft are specified. Cross wind tends to swing the ac during take-off and landing.
1. Anemometer for surface wind speed
2. Wind Vane for surface wind direction
3. RAWIN & P B Ascents for Upper Winds- by tracking hydrogen filled balloons by Radar & Optical Theodolite respectively.
Wind Vane & Anemometer
Exposure of Wind Instruments
Surface wind is recorded by installing wind vane and anemometer at a height of 10m in area free from obstructions. The wind is averaged for 10 minutes for all weather observations. For take offs & landing surface wind is averaged for 2 minutes.
Gust & Lull
A gust is an irregular and rapid fluctuation in the wind speed. Gusts are caused by turbulence due to ground friction and by uneven heating of the ground, especially in hot afternoons. The +ve fluctuations are gusts and –ve fluctuations are lulls.
1. is defined as sudden increase in wind speed by 32 kmh (16kt), should last for one minute or more and speed should increase to 44 (kmh) or more. Squall is associated with large CB clouds and violent convective activity, Squalls extend some km horizontally and several thousands of feet vertically. Both speed and direction in squall may differ significantly from prevailing winds.
2. Violent squalls are associated with Norwesters, Thunderstorms & Dust storms from March to June.
Gale is defined as persistent mean wind of speed 34 kt or more. It is associated with depressions and cyclonic storms.