Types of winds is one one the most important topics in geography. Both UPSC prelims and IAS mains exam GS paper 2 contains these topics. It is really important for the student to undestand the basic concept of this topic as both prelims and mains give equl importance to this topic. The factual data should be remembered with the concept. For such topics aspirants should should make separate notes for IAS prelims and IAS mains exam. also the candidates should be aware of the current affairs related to this topic.
- Classification of Winds
- Primary winds
- Secondary winds
- Local winds
CLASSIFICATION OF WINDS
Permanent winds or Primary winds or Prevailing winds or Planetary Winds
- The trade winds, westerlies and easterlies.
Secondary or Periodic Winds
- Seasonal winds: These winds change their direction in different seasons. For example monsoons in India.
- Periodic winds: Land and sea breeze, mountain and valley breeze.
- These blow only during a particular period of the day or year in a small area.
- Winds like Loo, Mistral, Foehn, Bora.
- The winds blowing throughout the year from one latitude to another in response to latitudinal differences in air pressure are called “planetary or prevailing winds”. They involve large areas of the globe.
- These are the planetary winds which blow extensively over continents and oceans.
- The two most well- understood and significant winds for climate and human activities are trade winds and westerly winds.
- The trade winds are those blowing from the sub-tropical high pressure areas towards the equatorial low pressure belt.
- Therefore, these are confined to a region between 30°N and 30°S throughout the earth’s surface.
- They flow as the north-eastern trades in the northern hemisphere and the south-eastern trades in the southern hemisphere.
- This deflection in their ideally expected north-south direction is explained on the basis of Coriolis force and Farrel’s law.
- Trade winds are descending and stable in areas of their origin (sub-tropical high pressure belt), and as they reach the equator, they become humid and warmer after picking up moisture on their way.
- The trade winds from two hemispheres meet at the equator, and due to convergence they rise and cause heavy rainfall.
- The eastern parts of the trade winds associated with the cool ocean currents are drier and more stable than the western parts of the ocean.
- The westerlies are the winds blowing from the sub-tropical high pressure belts towards the sub polar low pressure belts.
- They blow from southwest to north-east in the northern hemisphere and north-west to south-east in the southern hemisphere.
- The westerlies of the southern hemisphere are stronger and persistent due to the vast expanse of water, while those of the northern hemisphere are irregular because of uneven relief of vast land-masses.
- The westerlies are best developed between 40° and 65°S latitudes. These latitudes are often called Roaring Forties, Furious Fifties, and Shrieking Sixties – dreaded terms for sailors.
- The poleward boundary of the westerlies is highly fluctuating. There are many seasonal and short-term fluctuations. These winds produce wet spells and variability in weather.
- The Polar easterlies are dry, cold prevailing winds blowing from north-east to south-west direction in Northern Hemisphere and south-east to north-west in Southern Hemisphere.
- They blow from the polar high-pressure areas of the sub-polar lows.
- Periodic winds change their direction periodically with the change in season,
- Monsoons are the best example of large-scale modification of the planetary wind system.
- Other examples of periodic winds include land and sea breeze, mountain and valley breeze, cyclones and anticyclones, and air masses.
- Monsoons were traditionally explained as land and sea breezes on a large scale. Thus, they were considered a convectional circulation on a giant scale.
- The monsoons are characterized by seasonal reversal of wind direction.
- During summer, the trade winds of southern hemisphere are pulled northwards by an apparent northward movement of the sun and by an intense low pressure core in the north-west of the Indian subcontinent.
- While crossing the equator, these winds get deflected to their right under the effect of Coriolis force.
- These winds now approach the Asian landmass as south-west monsoons. Since they travel a long distance over a vast expanse of water, by the time they reach the south-western coast of India, they are over-saturated with moisture and cause heavy rainfall in India and neighboring countries.
- During winter, these conditions are reversed and a high pressure core is created to the north of the Indian subcontinent. Divergent winds are produced by this anticyclonic movement which travels southwards towards the equator. This movement is enhanced by the apparent southward movement of the sun. These are north-east or winter monsoons which are responsible for some precipitation along the east coast of India.
- Summer monsoon is called South Westerly Wind and is characterized by highly variable weather with frequent spells of drought and heavy rains. The winter monsoon is a gentle drift of air in which winds blow from the north-east and is known as North Easterly Wind.
- The monsoon winds flow over India, Pakistan, Bangladesh, Myanmar (Burma), Sri Lanka, the Arabian Sea, Bay of Bengal, southeastern Asia, northern Australia, China and
- Outside India, in the eastern Asiatic countries, such as China and Japan, the winter monsoon is stronger than the summer monsoon. (we will study about monsoons in detail while studying Indian Climate)
Land Breeze / Sea breeze
- At night, land masses cool quicker than sea due to rapid radiation which results in high pressure over land and low pressure over sea. And in calm, cloudless weather, air blows from land to sea. This breeze carries no moisture and is little warm and dry.
- In day time, the land being hotter than the sea develops low air pressure and the sea being cool develops high pressure. The air over land rises and is replaced by a cool breeze known as Sea Breeze from the sea, carrying some moisture.
Valley Breeze/ Mountain Breeze
- In mountainous regions, during the day the slopes get heated up and air moves upslope and to fill the resulting gap the air from the valley blows up the valley. This wind is known as the valley breeze. During the night the slopes get cooled and the dense air descends into the valley as the mountain wind. The cool air, of the high plateaus and ice fields draining into the valley is called katabatic wind.
- Another type of warm wind (katabatic wind) occurs on the leeward side of the mountain ranges. The moisture in these winds, while crossing the mountain ranges condense and precipitate. When it descends down the leeward side of the slope the dry air gets warmed up by adiabatic process. This dry air may melt the snow in a short time
- The local difference in temperature and pressure causes local winds. It is of four types: hot, cold, convectional and slope.
- Local differences of temperature and pressure produce local winds.
- Such winds are local in extent and are confined to the lowest levels of the troposphere. Some examples of local winds are discussed below.
COLD WINDS - Pampero, Gregale, Bora, Mistral
WARM WINDS - Loo, Chinook, Zonda, Sirocco
- Beneficial Wind
- Foehn like winds in USA and Canada move down the west slopes of the Rockies and are known as
- It is beneficial to ranchers east of the Rockies as it keeps the grasslands clear of snow during much of the winter.
- Harmful Wind
- Mistral is one of the local names given to such winds that blow from the Alps over France towards the Mediterranean Sea.
- It is channeled through the Rhine valley. It is very cold and dry with a high speed.
- It brings blizzards into southern France.
- Harmful Wind
- Sirocco is a Mediterranean wind that comes from the Sahara and reaches hurricane speeds in North Africa and Southern Europe.
- It arises from a warm, dry, tropical air mass that is pulled northward by low-pressure cells moving eastward across the Mediterranean Sea, with the wind originating in the Arabian or Sahara deserts. The hotter, drier continental air mixes with the cooler, wetter air of the maritime cyclone, and the counter-clockwise circulation of the low propels the mixed air across the southern coasts of Europe.
- The Sirocco causes dusty dry conditions along the northern coast of Africa, storms in the Mediterranean Sea, and cool wet weather in Europe.
Ths article gives you clear idea of the type of winds and its examples. It is the requirement of UPSC exam that aspirants are very well versed with this topic as many quetions in prelims and mains come from this topic. To read more articles on geography and atmosphere click here