Winds: Classification and types

What are winds? How do winds originate? What are the classifications and types? Read to know more.

The horizontal movement of air is described as the wind caused by the heating of the sun and the rotational movement of the earth.

Flow and direction are controlled by the following geographical factors and processes:

1. Pressure gradient force: This force provides initial flow and direction to the wind. The flow is from high pressure to low pressure and it is at right angles to isobars. The velocity of wind is directly proportional to pressure gradient force.
2. Coriolis force/deflection force: The force that deflects the direction of the wind is called deflection force. They are deflected to the right (concerning their source) in the northern hemisphere and the left in the southern hemisphere.
3. Friction force generated by surface: It is a restraining force on the flow of the wind. The amount of friction is an outcome of surface irregularities and the orientation of natural landforms. Friction is least above smooth oceanic surfaces. The frictional force is effective up to a height of a few thousand meters only.

Classification

Permanent winds

These are also called invariable or planetary wind systems because they blow over larger areas of the Earth. They blow in the same direction throughout the year.

Trade wind

• These flow from subtropical high-pressure belts to equatorial low-pressure belts in both hemispheres north and south.
• These are known as Northeast trade winds in the northern Hemisphere and southeast trade winds in the southern Hemisphere.
• Their direction of movement is NE to SW in the northern hemisphere and SE to NW in the southern hemisphere.

Westerlies

• Westerlies flow from subtropical high-pressure belts to sub-polar low-pressure belts to both hemispheres north and south.
• Their direction of movement is SW to NE in the northern hemisphere and NW to SE in the southern hemisphere.
• The dominance of land in the northern hemisphere makes westerlies less effective due to obstruction.
• Westerlies are vigorous in the southern hemisphere, hence due to the sound, they generate they are also called-
  1. Roaring forties between 40º-50ºS latitudes
  2. Furious fifties at 50ºS latitude
  3. Shrieking sixties at 60ºS latitudes

• These are on-shore throughout the year on the west coast of continents in mid-latitudes, hence causing rains over the western coasts.

Polar wind

• They flow from polar high-pressure belts to subpolar low-pressure belts in both hemispheres north and south.
• Their direction is NE to SW in the northern hemisphere and SE to NW in the southern hemisphere.
• They are stronger and intensified during the winter season and are responsible for causing blizzards.

Secondary or seasonal winds

These winds change their directions with the seasonal changes or periodically.

Monsoon wind

• A monsoon wind is a seasonal wind found especially in Asia that reverses direction between summer and winter and often brings heavy rains.
• The Asiatic monsoon is the result of the interaction of both the planetary wind system and regional factors, both at the surface and in the upper troposphere.

Land and sea breeze

• The periodicity of land and sea breezes change according to day and night and these are winds of coastal regions.
• The land and sea absorb and transfer heat differently. During the day the land heats up faster and becomes warmer than the sea.
• Over the land, the air rises giving rise to a low-pressure area, whereas the sea is relatively cool and the pressure overseas is relatively high. Thus, a 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.

Valley and mountain breeze

• In the mountains, during the day the slopes get heated up and air moves upwards and the air from the valley blows up the valley to fill the resulting gap. 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 from mountains draining into the valley is called katabatic wind.
• Another warm wind occurs on the leeward side of the mountain ranges. The moisture in it, while crossing the mountain ranges condenses and precipitates. When it descends the leeward side of the slope the dry air gets warmed up by the adiabatic process. This dry air may melt the snow in a short time.

Tertiary or local wind

These are the types of wind blowing in a particular locality. Local differences in temperature and pressure produce local winds. Such type of wind is local in extent and is confined to the lowest levels of the troposphere.

Some examples are discussed below:

The Wind system causes the evolution of various landforms on the earth’s surface as it is the main geomorphic agent shaping various landforms. You can read more about the Erosion and Depositional action of winds here.