Periodic Winds, Monsoon Winds, Local Winds, Hot Winds Part 3

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Periodic Winds: The direction of these winds changes with the change of seasons. The most important periodic wind is monsoon winds.

Monsoon Winds

The word Monsoon has been derived from the Arabic word Mausim meaning season. The winds that reverse their direction with the change of seasons are termed monsoon winds. During summer the monsoon winds blow from sea towards land, and during winter from land towards seas. The monsoon is generally accepted as seasonal modification of the general planetary wind system.

The Asiatic monsoon is the result of the interaction of both planetary wind system and regional factors, both at the surface and in the upper troposphere. India, Pakistan, Bangladesh, Myanmar, Sri Lanka, the Arabian Sea, the Bay of Bengal, south-east Asia, north Australia, China, and Japan are important regions where monsoon winds are prevalent.

Image of winter and summer monsoon

Image of Winter and Summer Monsoon

Image of winter and summer monsoon

Local Winds: Local winds usually affect small areas and are confined to the lower levels of the troposphere. Some of the local winds are as follows:

Land and Sea Breezes: Land and sea breezes are prevalent on the narrow strips along the coasts or a lake. It is a diurnal cycle in which the differential heating of land and water produces low and high pressures. During the day when landmass gets heated more quickly than the adjoining sea or large lake, the air expands and rises. Sea breeze then develops, blowing from the water having high pressure towards the land having low pressure. The sea breeze begins to develop shortly before noon and generally reaches its greatest intensity during mid-day to late afternoon. These cool winds have a significant moderating influence in coastal area.

Image of sea breeze

Image of Sea Breeze

Image of sea breeze

At night, the land and the air above it cools more quickly than the nearby water body. As a result, land has high pressure while the sea has comparatively low-pressure area. Gentle wind begins to blow from land having high pressure towards sea having low pressure. This is known as land breeze.

The Mountain and Valley Breezes: On a warm sunny day the mountain slopes are heated more than the valley floor. Hence, the pressure is low over the slopes while it is comparatively high in the valleys below. As a result, gentle wind begins to blow from valley towards slopes and it is termed as valley breeze.

After sunset, the rapid radiation takes place on the mountain slopes. Here, high pressure develops more rapidly than on the valley floor. Cold arid heavy air of mountain slopes starts moving down towards the valley floor. This is known as the mountain breeze.

Valley Breeze and Mountain Breeze

Valley Breeze and Mountain Breeze

Valley Breeze and Mountain Breeze

The valley and mountain breezes are also known as anabatic and katabatic breezes, respectively.

Hot Winds: The important hot winds of local category are:

  • Loo: Loo are hot and dry winds, which blow very strongly over the northern plains of India and Pakistan in the months of May and June. They blow from west to east and are usually experienced in the afternoons. Their temperature varies between to .

  • Foehn: Foehn is strong, dusty, dry, and warm local wind which develops on the leeward side of the Alps mountain ranges. Regional pressure gradient forces the air to ascend and cross the barrier. Ascending air sometimes causes precipitation on the windward side of the mountains. After crossing the mountain crest, the Foehn winds starts descending on the leeward side or northern slopes of the mountain as warm and dry wind. The temperature of the winds varies from which help in melting snow. Thus, making pasture land ready for animal grazing and help the grapes to ripe early.

  • Chinook: Chinook is the name of hot and dry local wind which moves down the eastern slopes of the Rockies in U.S.A. and Canada. The literal meaning of chinook is snow eater as they help in melting the snow earlier. They keep the grasslands clear of snow. Hence, they are very helpful to ranchers.

Cold Winds: The local cold winds originate in the snow-capped mountains during winter, and move down the slopes towards the valleys. They are known by different names in different areas.

S Mistral

Mistrals are most common local cold winds. They originate on the Alps, and move over France towards the Mediterranean Sea through the Rhone valley. They are very cold, dry, and high velocity winds. They bring down temperature below freezing point in areas of their influence. People in these areas protect their orchards and gardens by growing thick hedges and build their houses facing the Mediterranean Sea.