Local Winds


Local winds usually affect small areas and are confined to the lower levels of the troposphere.

Some of the local winds are given below –

[1] Land and Sea Breezes

Land and sea breezes are prevalent on the narrow strips along the coasts or a lake.

It is a diurnal (daily) 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; air expands and rises.

This process produces a local low pressure area on land.

Sea breeze then develops, blowing from the water (high pressure) towards the land (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.

 

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 a low pressure area.

Gentle wind begins to blow from land (high pressure) towards sea (low pressure).

This is known as land breeze.

 

[2] 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 assumes the name of 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.

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

 

[3] Hot 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 wind varies 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.

 

[4] 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.

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.