Types of Winds
The wind is a direction and speed-dependent air movement. It consists of gusts and eddies that can only be felt, unlike rain and snow. The sand shifts, the trees sway, the leaves fall, and the hair flies due to the wind. Because wind cannot be seen, a weathercock or weather vane is a standard device that is used to estimate wind direction.
Read More: Pressure Belts
Classification of Winds
There are majorly three Types of Winds that exist in the world. The winds are categorized or classified under the following categories:
|Planetary winds/Permanent Winds||Periodic Winds||Local Winds|
Read More: Heat Zones of Earth
Types of Planetary Winds
All year long, primary or planetary winds travel in one direction from high-pressure bands to low-pressure belts. They sweep across vast portions of continents and oceans. The planetary wind circulation is made up of trade winds, westerlies, and polar easterlies. The air in the Inter-Tropical Convergence Zone (ITCZ) rises because of convection currents due to high insolation and low pressure.
1. Trade Winds
The winds from the tropics converge in this pressure zone (ITCZ). The converged air rises along up. It reaches the top of the troposphere. Gradually, it moves towards the poles resulting in the accumulation of air at about 30 degrees North and South. Part of this accumulated air sinks to the ground. It forms a subtropical high. Sinking is also due to the cooling of the air at 30 degrees N and S latitudes. The air flows towards the equator near the land surface as the trade winds. Because of the Coriolis force, their direction becomes north-east and south-east in the northern and southern hemispheres respectively. Easterlies from either side of the equator converge at the Inter Tropical Convergence Zone (ITCZ). Thus, winds originating at ITCZ come back in a circular fashion. Such a tropical cell is called Hadley Cell.
Read More: Temperature Inversion
2. The Westerlies
In the middle latitudes (30 degrees -60 degrees) the circulation is that of sinking cold air. This air comes from the poles and the rising warm air that blows from the subtropical high-pressure belt. These winds are deflected due to Coriolis force and become westerly in both hemispheres. The deflected wind is called westerlies. These winds meet along the sub-polar low-pressure belt to raise high in the troposphere. From here, air moves away in both directions – towards the pole and equator. These winds start descending down above the sub-tropical high-pressure belt and polar high-pressure belt to form cells. These cells are called Ferrel cells and Polar cells respectively.
In terms of intensity and direction, the dominant westerlies vary more than the trade winds. There are more frequent invasions of polar air masses along with the travelling cyclones and anticyclones. These travelling cells of low and high pressures affect the movement of westerlies. The westerlies are stronger in the cold. In the southern hemisphere, westerlies are so powerful and persistent due to the absence of land between 40 – 60 degrees S that these are called ‘roaring forties’, ‘furious fifties’ and ‘screaming sixties’ along 40 degrees S, 50 degree S, and 60 degree S latitudes.
3. The Polar Easterlies
Winds move away from polar high pressure to sub-polar low pressure along the surface of the earth in the Polar cell. Their direction becomes easterlies due to Coriolis’s force. These are called polar easterlies.
Winds coming from the subtropical and the polar high belts converge and produce cyclonic storms/low-pressure conditions. This zone of convergence is called the polar front (see fronts and cyclones).
Read More: Heat Transfer Methods
Types of Periodic Winds
The term “secondary winds” refers to winds that change direction during the year. Other names for secondary winds include seasonal or periodic or cyclical winds. Secondary winds occur all throughout the world in a variety of settings.
Seasonal wind direction reversal is a hallmark of monsoons. They are explained as land and sea breezes on a large scale. A detailed description has been provided on the topic of the Monsoon chapter in the Indian climatology section.
2. Land Breeze and Sea Breeze
It is a diurnal cycle of local wind in coastal areas. It is caused due to the differential heating of land and water, which produces low and high pressures. The land gets heated more quickly than surrounding water during the daytime which results in the rising of warm air and the low-pressure area created over land. And, due to the high specific heat of water, it gets heated slowly. and a high-pressure zone created over the surface of the water. The specific heat of a substance refers to the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.
Different substances have different specific heat values. Compared to the land, the water has a higher specific heat. That means more heat is required to be absorbed by the water than the land to heat up. Thus, the time taken by the land to heat up is much less than the time taken by water to heat up. In other words, the land heats up faster than the water. As the water heats up slowly a thermal high pressure is developed over the water. Thus, the pressure gradient is developed and this causes the air to blow from high pressure to low pressure i.e. from sea to land. This is called Sea breeze, which causes a cooling effect on coastal lands.
The sea breeze starts developing shortly before noon. It generally reaches its greatest intensity during mid-day to late afternoon. At night, the situation gets reversed. The land and the surrounding air cool more quickly than the nearby water body. Thus, land has high pressure while the sea has comparatively a low-pressure area. A gentle wind blows from the land towards the sea. This is known as a land breeze.
Read More: Isotherms
3. Valley Breeze and Mountain Breeze
The mountain and valley breezes are another class of daily wind reversals. During the daytime, the slopes get heated up more than the valleys. Hence, the pressure is low over the slopes while comparatively high in the valleys below. Air moves up from the slope. The wind blows from the valley to the slopes to fill the resulting void created due to the heating of the slopes. This wind is called the valley breeze or anabatic wind.
The valley breeze is accompanied by a cumulus cloud formation near mountain peaks to cause orographic rainfall. During the night, the slopes get cooled. The dense air descends into the valley as mountain wind. The cool air of higher places(high plateaus and ice fields) draining into the valley is called mountain breeze or katabatic wind.
Read More: Structure of the Atmosphere
Types of Local Winds
Local Winds or Tertiary winds is the term used to describe the wind that only blows in a limited area at specific times of the day or year. The difference in temperature and air pressure of a certain area causes the wind type. Tertiary or local winds might be classified as hot, frigid, ice-filled, dusty, or rich. Loo is a particular kind of scorching, ferocious local wind that blows over India’s northern plains. Here we are providing a complete List of Major Local Winds in detail.
Types of Winds Diagram
Below is an illustration of various Types of Winds:
Read More: Heat Waves
Types of Winds UPSC
Planetary or primary winds, trade winds, Westerlies, periodic winds, local winds, monsoon, land, sea, mountain, and valley breeze are some of the several types of winds that might exist. Both for the prelims and the mains of the UPSC IAS Exam, the subject of “Types of Wind” is crucial. Relevant information regarding wind and its types will be provided in this article.