13. Wind

13. WIND Defination • Due to horizontal abnormalities, air moves from the areas of high pressure to the areas of low pressure. • This horizontally moving air is called wind. Movement of the wind (a) Because of Coriolis force all winds are deflected to the right clockwise in the Northern Hemisphere. (b) While they are deflected to the left anticlock wise in the Southern Hemisphere with respect to the rotating earth. • Coriolis force also increases with the increasing wind velocity. • Since this phenomenon was firstly proved by a Frence scientist Ferrel, it is called Ferrel's Law Types of winds Type of Wind Prevailing wind Trade wind Westerlies wind Seasonal wind Local wind Polar wind Prevailing wind • It's other name is planetary wind • It's also known as permanent wind • The winds blowing almost in the same direction throughout the year are called pervailing winds. • Prevailing wind are three types (a) Trade winds (b) Westerlines winds (c) Polar winds (a) Trade winds– • These are the permanent winds blowing in both the hemispheres. • Trade winds are the winds having fixed paths. • Trade winds converge and rise causing convectional rainfall in the equatorial region near the equator. (b) Westerlies winds– • These winds are best developed in the 40º–65º latitudes. • Westerlis wind known as veries name due to its nature. (a) On 40º SLatitudes- These wind known as Roaring forties. (b) On 50ºS Latitudes- These wind known as Furious Fifties. (c) On 60º SLatitudes- These wind known as Shrieking Sixties. • These names are given by the sailors who wer being effected by those westerlies. (c) Polar winds– • Polar wind blows from the polar high-perssure belts to the sub-polar low pressure belts. • These wind have very low temperature. 2. Seasonal winds • Seasonal winds change their direction of blowing with the changing seasons. • These are also calee as Periodic winds. • Seasonal winds are of three types(a) Monsoon winds. (b) Land and Sea Breezes. (c) Mountain and Valley Breezes. 3. Local winds • This winds blow due to local variation in the tem perature and pressure. • These wind influence a very small area. • Hot local winds raise the temperature of the blowing area 27 • Cold local winds sometimes bring the temperature of the affected area below the freezing points. • These local winds blow in the lower layers of the Troposphere. Some important local winds are Chinook– • Chinook means the 'snow-eater' (adoped from the language of Red Indians). • This is the hot and dry wind blowing along the eastern slope of the Rockies • Chinook covers an area from the southern part of Colorado in the south to British Columbia in Canada in the North. • Due to its effect, the snow melts and green grass sprouts even in the winter. • This wind is helpful for the animal rearing as it makes the grasslands snow free. Foehn– • This is similar to Chinook and blows along the northern slope of the Alps. • It affects the Switzerland most. • It melts the snow, makes the weather pleasant and helps in early ripening of the grapes. Sirocco– • This is a Warm, dry and dusty wind. • It is blows in northerly direction from the Sahara Desert. • It's crossing over the Mediterranean Sea reaches Italy, Spain etc. • It is also known as Blood rain because of its redish sand brought alongwith it from Sahara desert. • It is very much destructive to agricultural and fruit crops. • There are different local names for Sirocco in Africa e.g. (a) Khamsin in Egypt (b) Gibli in Libya (c) Chilli in Tunisia. (d) Levanter in Spain (e) Leste in Maderia island Black Roller— • These are the warm and dry dusty winds, blowing in the great plains of North America. Yoma– • This is the warm and dry wind like 'Santa Ana', blowing in Japan. Temporal– • This is the monsoon wind blowing in the Central America. Simoom– • This is the warm and dry wind blowing in the Arabian Desert. • It causes dust storms and obstructs visibility. Samoon– • This is the wind blowing in the Kurdistan region of Iran and Iraq. • It has the characteristics similar to Foehn. Shamal– • This is the warm, dry and sandy wind, blowing in the deserts of Iran, Iraq and UAE. Seistan– • This is the high velocity northerly wind blowing in the eastern parts of Iran in summer. Haboob– • This is the fast blowing wind full of dust and sand. • It is blowing in the northern parts of Sudan, especially near Khartoum. • It obstructs visibility. • It is Causes rain with thunder storm. Karaburan– • These are the dust laden fast blowing winds in the Tarim Basin in the Central Asia. • These winds blow towards the North-East. Koimbang– • These are winds similar to Foehn. • It is blowing in Java (Indonesia). • It is harmful to the tobacco crop. Harmattan– • This is the warm and dry wind blowing from northeast and east to the west in the Sahara desert. • The weather becomes suddenly dry and pleasant in the western coast of Africa, at the arrival of Harmattan. • Therefore, it is called 'Doctor' in the Guinea coastal area. Brick Fielder– • This is the warm and dry wind blowing in the Victoria province of Australia. 28 Norwester– • This is the warm, dry and gusty wind blowing in northern New Zealand. Loo– • This is a hot and dry wind blowing in the northern India from the north west and west to the east. • It is sometimes called 'heat wave'. Santa Ana– • This is the warm and dry wind blowing in California (USA). Mistral– • This is the cold local wind blowing in Spain and France from north-west to south-east direction. • While blowing through the narrow valley of the Rhone River, they become stormy northerly cold winds. • The arrival of Mistral causes sudden drop in air temperature to below freezing point. Bora– • It is an extremely cold and dry north-easterly Sea. • It is similar to mistral and affects ltaly and Yugoslavia. Blizzard– • It is a violent stormy cold polar wind laden with dry snow. • It is prevalent in north and south Polar Regions. • These winds affect Canada and USA. • On the arrival of Blizzards, the air temperature drops below the freezing point. • In the Tundra and Siberian regions of Russia, it is known as Purga and Burran, respectively. Pampero– • These are the cold polar winds blowing very fast in the pampas region of South America. Juran– • These are the cold and dry winds. • It is blowing from the Jura Mountains (Switzerland) to the Geneva Lake (Italy), in night. Southern Burster – • This is a fast blowing cold and dry wind in New South Wales (Australia). JET STREAM • These are the winds blowing with great velocity near the Tropopause. • The jet streams are active in 150 km wide and 2-3 km thick transition belt. • The general velocity of these winds is about 150200 km/hour. • But sometime the velocity at the core of the jet stream is found to be 325 km/hour. • Jet streams are generally found in the North Hemisphere only. • They are found over the South Pole In the South Hemisphere. • They are found in the form of light Rossby Waves over other latitudes also. • The reason behind the origin of these jet streams is the difference in surface temperature and pressure gradient. • North- east Jetstream is responsible for rain is summer in India. 29