Classification of Winds | Geography for UPSC 2024 (Pre & Mains) PDF Download

 Page 1


 
 
CLASSIFICATION OF WINDS 
PERMANENT WINDS  
? The winds that blow almost in the same direction throughout the year 
are called Prevailing or Permanent winds. 
? They are really large air masses that are created mainly as a result of 
the earth’s rotation, the shape of the earth and the sun’s heating 
power. 
These include : 
1) Trade winds  
2) Westerlies  
3) Polar Easterlies 
( ALREADY DISCUSSED IN DETAILS – REFER TO PREVIOUS 
LECTURE FOR THE SAME) 
 
NOTE: 
1. Primary circulation  
planetary wind systems  
2. Secondary circulation  
cyclone, anticyclones, monsoons and air masses.  
3. Tertiary circulation  
 local winds 
VARIABLE WINDS  
Seasonal Wind  
The pattern of wind circulation is modified in different seasons due to the 
shifting of regions of maximum heating, pressure and wind belts. The most 
pronounced effect of such a shift is noticed in the monsoons, especially over 
southeast Asia 
Land and Sea Breezes  
Page 2


 
 
CLASSIFICATION OF WINDS 
PERMANENT WINDS  
? The winds that blow almost in the same direction throughout the year 
are called Prevailing or Permanent winds. 
? They are really large air masses that are created mainly as a result of 
the earth’s rotation, the shape of the earth and the sun’s heating 
power. 
These include : 
1) Trade winds  
2) Westerlies  
3) Polar Easterlies 
( ALREADY DISCUSSED IN DETAILS – REFER TO PREVIOUS 
LECTURE FOR THE SAME) 
 
NOTE: 
1. Primary circulation  
planetary wind systems  
2. Secondary circulation  
cyclone, anticyclones, monsoons and air masses.  
3. Tertiary circulation  
 local winds 
VARIABLE WINDS  
Seasonal Wind  
The pattern of wind circulation is modified in different seasons due to the 
shifting of regions of maximum heating, pressure and wind belts. The most 
pronounced effect of such a shift is noticed in the monsoons, especially over 
southeast Asia 
Land and Sea Breezes  
 
The land and sea absorb and transfer heat differently. During the day the 
land heats up faster and becomes warmer than the sea. Therefore, over the 
land the air rises giving rise to a low pressure area, whereas the sea is 
relatively cool and the pressure over sea is relatively high. Thus, pressure 
gradient from sea to land is created and the wind blows from the sea to the 
land as the sea breeze. In the night the reversal of condition takes place. 
The land loses heat faster and is cooler than the sea. The pressure gradient is 
from the land to the sea and hence land breeze results. 
Mountain and Valley Winds 
 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 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. 
Local Winds 
 Differences in the heating and cooling of earth surfaces and the cycles 
those develop daily or annually can create several common, local or 
regional winds. 
 
 
 
 
Page 3


 
 
CLASSIFICATION OF WINDS 
PERMANENT WINDS  
? The winds that blow almost in the same direction throughout the year 
are called Prevailing or Permanent winds. 
? They are really large air masses that are created mainly as a result of 
the earth’s rotation, the shape of the earth and the sun’s heating 
power. 
These include : 
1) Trade winds  
2) Westerlies  
3) Polar Easterlies 
( ALREADY DISCUSSED IN DETAILS – REFER TO PREVIOUS 
LECTURE FOR THE SAME) 
 
NOTE: 
1. Primary circulation  
planetary wind systems  
2. Secondary circulation  
cyclone, anticyclones, monsoons and air masses.  
3. Tertiary circulation  
 local winds 
VARIABLE WINDS  
Seasonal Wind  
The pattern of wind circulation is modified in different seasons due to the 
shifting of regions of maximum heating, pressure and wind belts. The most 
pronounced effect of such a shift is noticed in the monsoons, especially over 
southeast Asia 
Land and Sea Breezes  
 
The land and sea absorb and transfer heat differently. During the day the 
land heats up faster and becomes warmer than the sea. Therefore, over the 
land the air rises giving rise to a low pressure area, whereas the sea is 
relatively cool and the pressure over sea is relatively high. Thus, pressure 
gradient from sea to land is created and the wind blows from the sea to the 
land as the sea breeze. In the night the reversal of condition takes place. 
The land loses heat faster and is cooler than the sea. The pressure gradient is 
from the land to the sea and hence land breeze results. 
Mountain and Valley Winds 
 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 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. 
Local Winds 
 Differences in the heating and cooling of earth surfaces and the cycles 
those develop daily or annually can create several common, local or 
regional winds. 
 
 
 
 
 
 
IMPORTANT EXAMPLES: 
 
CHINOOK  
? Foehn like winds in USA and Canada move down the west slopes 
( leeward side) of the Rockies  
? It is beneficial to ranchers east of the Rockies as it keeps the 
grasslands clear of snow during much of the winter.This is why 
Chinook is also called as Snow Eater.   
? The rise in the temperature due to Chinook helps in early sowing 
of spring wheat in the USA. 
 
FOEHN  
? It is a strong, gusty, dry and warm wind which develops on the 
leeward side of  Alps mountains in Switzerland. 
Page 4


 
 
CLASSIFICATION OF WINDS 
PERMANENT WINDS  
? The winds that blow almost in the same direction throughout the year 
are called Prevailing or Permanent winds. 
? They are really large air masses that are created mainly as a result of 
the earth’s rotation, the shape of the earth and the sun’s heating 
power. 
These include : 
1) Trade winds  
2) Westerlies  
3) Polar Easterlies 
( ALREADY DISCUSSED IN DETAILS – REFER TO PREVIOUS 
LECTURE FOR THE SAME) 
 
NOTE: 
1. Primary circulation  
planetary wind systems  
2. Secondary circulation  
cyclone, anticyclones, monsoons and air masses.  
3. Tertiary circulation  
 local winds 
VARIABLE WINDS  
Seasonal Wind  
The pattern of wind circulation is modified in different seasons due to the 
shifting of regions of maximum heating, pressure and wind belts. The most 
pronounced effect of such a shift is noticed in the monsoons, especially over 
southeast Asia 
Land and Sea Breezes  
 
The land and sea absorb and transfer heat differently. During the day the 
land heats up faster and becomes warmer than the sea. Therefore, over the 
land the air rises giving rise to a low pressure area, whereas the sea is 
relatively cool and the pressure over sea is relatively high. Thus, pressure 
gradient from sea to land is created and the wind blows from the sea to the 
land as the sea breeze. In the night the reversal of condition takes place. 
The land loses heat faster and is cooler than the sea. The pressure gradient is 
from the land to the sea and hence land breeze results. 
Mountain and Valley Winds 
 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 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. 
Local Winds 
 Differences in the heating and cooling of earth surfaces and the cycles 
those develop daily or annually can create several common, local or 
regional winds. 
 
 
 
 
 
 
IMPORTANT EXAMPLES: 
 
CHINOOK  
? Foehn like winds in USA and Canada move down the west slopes 
( leeward side) of the Rockies  
? It is beneficial to ranchers east of the Rockies as it keeps the 
grasslands clear of snow during much of the winter.This is why 
Chinook is also called as Snow Eater.   
? The rise in the temperature due to Chinook helps in early sowing 
of spring wheat in the USA. 
 
FOEHN  
? It is a strong, gusty, dry and warm wind which develops on the 
leeward side of  Alps mountains in Switzerland. 
 
? The weather becomes quite pleasant in the valleys due to melting 
of snow. The wind helps animal grazing by melting snow .These 
winds helps in early sowing of wheat, ripening of grapes and 
check autumn frost. 
? This is why valleys of Switzerland are called "Climatic Oasis" 
during winter season .  
 
 
HARMATTAN 
The warm and dry winds blowing from north-east and east to west in 
the parts of Sahara Desert are called Harmattan.  
These winds become extremely dry because of their journey over 
Sahara desert.  This is why Harmattan is known as "Doctor' in the 
Guinea coastal area of western Africa  
 
SIROCCO  
? Sirocco is a Mediterranean wind that comes from the Sahara and 
dusty local winds, which blows in northerly direction from 
Sahara desert and after crossing over the Mediterranean sea it 
reaches Italy, Spain etc.  
? Sirocco, while passing over the Mediterranean Sea picks up 
moisture and yields rainfall in the southern part of Italy, where 
the rain associated with Sirocco is called "Blood Rain" because 
of fallout of red sands with falling rains. 
? The Sirocco causes dusty dry conditions along the northern coast 
of Africa, storms in the Mediterranean Sea, and cool wet 
weather in Europe. 
? It is apparent that Sirocco is very much injurious to agricultural 
and fruits crops.  
 
 
Page 5


 
 
CLASSIFICATION OF WINDS 
PERMANENT WINDS  
? The winds that blow almost in the same direction throughout the year 
are called Prevailing or Permanent winds. 
? They are really large air masses that are created mainly as a result of 
the earth’s rotation, the shape of the earth and the sun’s heating 
power. 
These include : 
1) Trade winds  
2) Westerlies  
3) Polar Easterlies 
( ALREADY DISCUSSED IN DETAILS – REFER TO PREVIOUS 
LECTURE FOR THE SAME) 
 
NOTE: 
1. Primary circulation  
planetary wind systems  
2. Secondary circulation  
cyclone, anticyclones, monsoons and air masses.  
3. Tertiary circulation  
 local winds 
VARIABLE WINDS  
Seasonal Wind  
The pattern of wind circulation is modified in different seasons due to the 
shifting of regions of maximum heating, pressure and wind belts. The most 
pronounced effect of such a shift is noticed in the monsoons, especially over 
southeast Asia 
Land and Sea Breezes  
 
The land and sea absorb and transfer heat differently. During the day the 
land heats up faster and becomes warmer than the sea. Therefore, over the 
land the air rises giving rise to a low pressure area, whereas the sea is 
relatively cool and the pressure over sea is relatively high. Thus, pressure 
gradient from sea to land is created and the wind blows from the sea to the 
land as the sea breeze. In the night the reversal of condition takes place. 
The land loses heat faster and is cooler than the sea. The pressure gradient is 
from the land to the sea and hence land breeze results. 
Mountain and Valley Winds 
 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 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. 
Local Winds 
 Differences in the heating and cooling of earth surfaces and the cycles 
those develop daily or annually can create several common, local or 
regional winds. 
 
 
 
 
 
 
IMPORTANT EXAMPLES: 
 
CHINOOK  
? Foehn like winds in USA and Canada move down the west slopes 
( leeward side) of the Rockies  
? It is beneficial to ranchers east of the Rockies as it keeps the 
grasslands clear of snow during much of the winter.This is why 
Chinook is also called as Snow Eater.   
? The rise in the temperature due to Chinook helps in early sowing 
of spring wheat in the USA. 
 
FOEHN  
? It is a strong, gusty, dry and warm wind which develops on the 
leeward side of  Alps mountains in Switzerland. 
 
? The weather becomes quite pleasant in the valleys due to melting 
of snow. The wind helps animal grazing by melting snow .These 
winds helps in early sowing of wheat, ripening of grapes and 
check autumn frost. 
? This is why valleys of Switzerland are called "Climatic Oasis" 
during winter season .  
 
 
HARMATTAN 
The warm and dry winds blowing from north-east and east to west in 
the parts of Sahara Desert are called Harmattan.  
These winds become extremely dry because of their journey over 
Sahara desert.  This is why Harmattan is known as "Doctor' in the 
Guinea coastal area of western Africa  
 
SIROCCO  
? Sirocco is a Mediterranean wind that comes from the Sahara and 
dusty local winds, which blows in northerly direction from 
Sahara desert and after crossing over the Mediterranean sea it 
reaches Italy, Spain etc.  
? Sirocco, while passing over the Mediterranean Sea picks up 
moisture and yields rainfall in the southern part of Italy, where 
the rain associated with Sirocco is called "Blood Rain" because 
of fallout of red sands with falling rains. 
? The Sirocco causes dusty dry conditions along the northern coast 
of Africa, storms in the Mediterranean Sea, and cool wet 
weather in Europe. 
? It is apparent that Sirocco is very much injurious to agricultural 
and fruits crops.  
 
 
 
MISTRAL  
? 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. 
? These stormy winds adversely affect airflights.  
? The arrival of mistral causes sudden drop in air temperature to 
below freezing point. 
 
Santa Ana 
? Santa Ana is a dry and warm local wind that occurs in the Santa Ana 
Valley of Southern California and it is almost similar to Chinook or 
Foehn with regard to thermal and moisture characteristics. 
? Santa Ana winds are so dry and warm that they pose a great danger to 
the Californian Orchards and are considered as Climatic Hazard 
since they desiccate (dry) the soil and vegetation moisture and may 
even result into widespread forest fires. 
 
Khamsin 
? These are warm, dry, dusty (containing sand particles) local winds 
that blow in Northern Africa (Egypt) and Arabia. 
 
Loo 
? It originates from the Thar desert and has north-westerly to a westerly 
direction. 
? They dominate during early summer in the months of March to May and 
create heat waves like condition in Northern India and adjoining parts.