Local Winds

Loo, Foehn and Chinook are important hot winds of local category.

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.
• Their direction is from west to east and they are usually experienced in the afternoons.
• Their temperature varies between 45°C to 50°C.

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 vary from 15°C to 20°C 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.

The Santa Ana

• A hot, dry, strong, blustery, föhn-type wind which blows from the north-east or east over southern California and carries with it large quantities of dust.
• It is most frequent in winter but may also occur in spring or autumn.
• It may get its name from the Santa Ana Mountains or the Santa Ana Canyon but other possibilities are that it derives from santanas, meaning ‘devil winds’, or the Spanish Satanás, meaning Satan.
• These winds can cause a great deal of damage.
• As they are hot and dry, they cause vegetation to dry out, so increasing the risk of wildfires; and once fires start the winds fan the flames and hasten the spread of the fires. In spring, Santa Ana winds can cause considerable damage to fruit trees.

Sirocco

• Sirocco is a Mediterranean windthat 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.

Harmattan

• The warm and dry winds blowing from north­east and east to west in the eastern parts of Sahara desert are called harmattan.
• These winds become ex­tremely dry because of their journey over Sahara desert.
• While blowing over Sahara desert these winds pick up more sands mainly red sands.
• The western coast of Africa is warm and moist and hence the weather becomes unpleasant because the weather con­ditions characterized by high temperature and high relative humidity become injurious for human health.
• The weather becomes suddenly dry and pleasant at the arrival of harmattan as the relative humidity of the air is remarkably reduced due to high temperature and hyperaridity of harmattan.
• This is why harmattan is known as ‘doctor’ in the Guinea coastal area of western Africa.
• In fact, harmattan is very dusty and stormy wind blowing with so gusty speed that trees are up­rooted.
• These winds are usually associated with dust storms resulting into marked reduction in the visibil­ity.
• Harmattan becomes more vigorous during summer months.
• In fact, harmattan is a special type of north­east trade wind.
• It becomes extremely warm wind because of hot and dry desert of Sahara.
• Similar warm, dry, very strong and dust-laden winds arc called ‘brick-fielder’ in Victoria province of Australia, ‘black-roller’ in the Great Plains of the USA, ‘shamal’ in Mesopotamia and Persian Gulf, and ‘norwester’ in New Zealand.

The Khamsin

• A hot, dry, dust-laden, southerly wind over Egypt, the Red Sea and eastern parts of the Mediterranean Sea ahead of eastward-moving depressions.
• It occurs during the period February to June, being most frequent in March and April.
• The Khamsin is a Sirocco wind, whose name comes from the Arabic word for ‘fifty’, which is approximately the length of time the wind blows for. In the nineteenth Century, the plague was worst in Egypt when the Khamsin was blowing.