KERALA PSC / PHYSICAL GEOGRAPHY / WINDS / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE

 

KERALA PSC / PHYSICAL GEOGRAPHY / WINDS / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE

KERALA PSC / PHYSICAL GEOGRAPHY / WINDS / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE

·      A wind can be defined as a stream of air in a fairly well-defined direction. Winds are generated due to differences in pressure from one place to the other.

·      Wind is ‘air in motion’ and plays an important role in climatic variations on the earth

·      Air always moves from a region of high pressure to a region of low pressure

·      The Auroras are the rolling lights in the atmosphere which are visible in the high latitude regions.

·      It is called Aurora Borealis in the Artic Zone and Aurora Australis in the Antartic zone.

·      Albedo is the percentage of radiant energy reflected back by the surface

·      The winds blowing in the Northern Hemisphere are deflected to their right and those blowing in the Southern hemisphere to their left under the Coriollis effect. This principle of deflection is called Ferrel’s Law. Ferrel’s law is a law postulated in 1856 by the American scientist William Ferrel

·      Planetary winds are permanent winds which blow throughout the year from one latitude to the other in response to the latitudinal differences in air pressure. They blow over the vast areas of continents and oceans. Eg: trade winds and westerlies and polar winds

·      Trade winds refers to the winds that blows from the sub-tropical belts of high pressure towards the equatorial region of low pressure.

·      Trade winds blow towards the equator between 5º and 30ºnorth and south latitude

·      The word ‘trade’ comes from the saxon word ‘tredon’ which means ‘to tread and follow a regular path.’

·      Trade winds are also called tropical easterlies

·      Trade winds are called so because prior to the steamage; sailing ships carrying goods of trade and cargo depended on these winds.

·      Doldrums are equatorial belts of low pressure where the north-east and south-east trade winds converge on and meet each other approximately between 5º south and 5º north latitude. The belt is characterized by extremely low pressure with calm conditions

·      Westerlies or Anti-Trade winds are regular winds which blows outside the tropics in the temperate zone. These winds blow from the sub-tropical high pressure areas to sub-polar low pressure areas and between 35º and 60º North and South latitudes

·      Roaring Forties are powerful westerly winds that blow throughout the year over the oceans of the southern hemisphere between 40º and 60º south latitudes. They are called Best brave winds and bring storms and heavy rainfall.

·      The winds which developed between 45º and 55º are called Furious Fifties and that developed between 55º and 65º are called Shrieking sixties. These are the dreaded terms used by sailors.   

·      Polar Easterlies constitute the wind system characteristic of the arctic and polar zones. They extend from about 60º north and 60º south latitude to the poles.

·      Secondary or Periodic Winds: The winds that change their direction periodically with the change in season, are called secondary or periodic winds. Eg: Monsoon winds

·      Monsoon winds are seasonal winds which blow briefly over India, Sri Lanka, China and North West Australia

·      Monsoon climate is marked by summer rains and winter droughts

·      The word ‘monsoon’ derived its name from the Arabic word ‘mausin’ meaning seasonal winds. Traditionally monsoon has been considered as a result of the differential heating of land and sea

·      According to dynamic theory, monsoon are a result of the shift of the Inter Tropical Convergence Zone (ITCZ) under the influence of the vertical sun.

·      Horse Latitudes are sub-tropical belts of variable winds and columns that lie between the latitudes of 25º and 35º North and South. They coincide with the sub-tropical high pressure belts.

·      Horse Latitude winds are weak and shifting. In early days, the sailing vessels with a cargo of horses found it difficult to sail under such calm conditions. They used to throw horses into the sea to save valuable drinking water and this part therefore came to be called as Horse Latitudes.

·      Local winds develop as a result of the local differences in temperature and pressure. They affect the smaller areas and are restricted to the lowest levels of the troposphere.

·      Local winds include hot, cold, convectional and slope winds

·      The most famous local cold winds that blow from Alps over France towards the Mediterranean sea is the mistral.

·      Loos are very hot and dry local winds that blows from the west in the months of May and June, usually in afternoons in the plains of Northern India and Pakistan. Its temperature invariably varies between 45ºC and 50ºC. It may cause sun stroke to people.

·      Foehn is a hot wind of local importance in the Alps. It is a strong, gusty, dry and warm wind. It develops on the leeward side of a mountain range. Due to regional pressure gradient stable air is forced to ascend the windward side causing precipitation on the mountains.

·      Chinook is a local wind that moves down the Rockies. The word ‘chinook’ literary means ‘snow eater’. It keeps the grasslands clear from snow during much of the winter.

·      Local convectional winds are of two types – Land breeze and sea breeze

·      Land breeze is defined as the process by which cold winds blows from the land to sea during night. Land breeze is not as strong as the sea breeze.

·      During the day time, the land get warmer than the sea producing low pressure over the land into which cooler air moves from over the sea. The local winds that blows from sea to land during the day time is called Sea breeze

·      Valley breeze and mountain breeze are the counterparts of land and sea breeze. During the day time the slopes of the mountain gets heated more than the valley floor. As such the air from the valley flows up the slope. This is called the Valley breeze. After sunset the process is reversed. Rapid loss of heat through terrestrial radiation along the mountain slopes results in the sliding of cold dense air from higher elevations to valleys. This is called the mountain breeze.

·      Jet streams are narrow concentrated bands of meandering high velocity geotropic streams bounded by low speed winds and is a part of upper level westerlies.

·      The Jet streams have an average velocity of 120 km per hour in winter and 50km per hour in summer

·      A hurricane is a strong wind whose speed exceeds 121 km/hr

·      Cyclones are irregular wind movements involving closed air circulation around a low pressure centre. Cyclones are associated with destructive and violent disturbances such as heavy squalls and torrential rainfall.

·      Cyclones are called hurricanes in the South-East Carribean region

·      In the Philippines islands, Eastern China and Japan, cyclones are called Typhoons

·      Around South-East African coast, Madagascar, Mauritius islands and north-West Australia they are called Willie Willies

·      If the speed of cyclone is greater than 250 km/hr, it is known as Super Cyclone

·      Tornadoes are violently rotating storms, characterized by a funnel shaped cloud in which winds whirl around a small area of extremely low pressure. They are generally accompanied by torrential rains

·      Water Spout is a tornado occurring in the sea usually in tropical and sub-tropical regions which connects a whirling cone of dense cloud with a cone of spray raised from sea and thus raises a huge column of water

·      Anti-cyclone is a high pressure wind blowing outwards from the centre, clockwise in the Northern Hemisphere and anti-clockwise in the Southern Hemisphere

·      Coriolis force is a ‘fictious’ force needed to relate the movement of air masses over the earth’s surface to its rotating co-ordinate system (the grid). It was named after the French mathematician Gaspard de Coriolis, who first described it in 1835

·      Coriolis force is absent at the equator and increases towards the poles. The force is responsible for the formation and direction of movement of anti-cyclones and whirlpools.

KERALA PSC / PHYSICAL GEOGRAPHY / WINDS / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE