Wind and Wind Types UPSC Notes: Classification of Winds

The wind is defined as the movement of air mass from an area of high pressure to an area of low pressure. In other words, the horizontal movement of the air in response to the difference in pressure is known as wind. This variation in pressure is due to the rotation of the earth and the heating of air by the sun. Although both winds and air currents are formed as a result of the movement of air, they differ from each other. Winds are formed when the air moves horizontally in response to pressure, whereas the air moving in the vertical or nearly vertical direction is referred to as the air currents. Broadly, there are three types of winds – prevailing winds, seasonal winds and local winds.

In this article on types of winds, we shall discuss the broad classifications of winds and types of winds under each classification. This is an important topic under geography for UPSC CSE exams. It will be helpful for the aspirants in the upcoming examinations.

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What is Wind?

The heating of the Earth’s surface is uneven because the land gets heated up faster than the water bodies. As a result of this, the air above the hot surface rises and develops a low atmospheric pressure. This low-pressure area is filled by the cold air which moves from the area of high atmospheric pressure. Due to this horizontal movement of air, the winds are formed. The uneven distribution of pressure in the atmosphere is balanced by the winds. An instrument named Anemometer is used to measure the speed of the wind and another instrument called a wind vane is used to measure the direction of the wind.

Major Causes of Wind

The unequal temperature of two locations is the primary source of wind generating. Here are a few instances of the uneven warmth we observe in our environment:

• Seawater heats up more slowly than land does. 
• Conduction heats the air above the land as its temperature rises. 
• Warm air rises because its density is lower than that of the surrounding air, leaving a vacuum in its wake. 
• A chilly coastal wind is produced as the colder air from the sea rushes to fill the void. 
• There is a temperature differential between onshore and offshore during the night because the land cools down faster. 
• Once more, a pressure drop is brought about by this temperature differential, creating a land wind.

Factors Affecting the Movement of Winds

The winds generally move in all directions and at various speeds. There are 3 major forces which affect the horizontal movement of the air. They are the Coriolis force, the pressure gradient force and the frictional force. However, the Coriolis force is the major factor which affects the direction of winds.

Coriolis Force

• Due to the rotation of the Earth, the wind gets deflected from its original path rather than crossing the isobars at right angles as directed by the pressure gradient force. This effect on wind is known as the Coriolis effect.
• As a result of this effect, the wind in the southern hemisphere gets deflected towards the left side of their path and in the northern hemisphere, it gets deflected towards the right side of their path.
• This force is generally zero at the equator and maximum at the poles.

Pressure Gradient Force

• The force which is generated as a result of differences in horizontal pressures is known as the pressure gradient force.
• This force operates from a high-pressure area to a low-pressure area, which results in the movement of the wind.
• Whenever the isobars are closer, the pressure gradient force is strong and thus the wind also moves at a strong speed.

Frictional Force

• The movement of the wind is resisted by the frictional force that is developed due to the irregularities of the earth’s surface. The speed of the wind is retarted by this force.
• The horizontally moving air experiences less friction over the sea surfaces when compared to the uneven terrain.

Check the NCERT notes on extra tropical cyclones here.

Classification of Wind

The winds are broadly classified into three types. They are

• Permanent winds
• Seasonal winds
• Local winds

Let us have a brief overview of all the three types of winds.

Primary Or Permanent Winds

The permanent winds are the winds which blow from high-pressure belts to low-pressure belts constantly in the same direction throughout the year. They are also known as the primary or planetary winds. They not only blow over the continents but also over the seas and oceans.

There are three types of planetary winds and they are

• Trade winds
• Westerlies
• Polar Easterlies

Trade Winds

• These types of winds blow from subtropical high-pressure belts to equatorial low-pressure belts. Thus, the trade winds are confined to the region that lies between 30°N and 30°S.
• Since the trade winds mostly blow from the east, they are also known as the Tropical easterlies.
• Due to the Coriolis effect, the trade winds in the northern hemisphere blow in the north-east direction and in the southern hemisphere, they blow in the south-east direction.

Read the NCERT notes on factors controlling temperature distribution here.

Westerlies

• The Westerlies blow from subtropical high-pressure belts towards the sub-polar low-pressure belts.
• In the northern hemisphere, they blow from the south-west to the north-east and in the southern hemisphere, they blow from the north-west to the south-east. For this reason, they are named westerlies.
• Comparatively, the westerlies that blow in the southern hemisphere are stronger than that of the northern hemisphere. This is because in the southern hemisphere most of the region is covered by the ocean, whereas in the northern hemisphere, uneven relief of vast landmass is present whose frictional force retards the wind speed.

Polar Easterlies

• These winds blow from polar high-pressure belts to sub-polar low-pressure belts.
• In the northern hemisphere, the polar easterlies blow from the north-east to the south-west direction and in the southern hemisphere, they blow from the south-east to the north-west direction.

Study the NCERT notes on types of clouds here.

Secondary Or Seasonal Winds

The winds which change their direction periodically with the change in seasons are known as seasonal or periodic winds. One of the most important periodic winds is the monsoon wind.

Monsoon Winds

• These winds are characterized by the reversal of direction with the change in season.
• During winter, the monsoon winds blow from land towards the sea and during summer, they blow from the sea towards the land. On a large scale, land and sea breeze takes place during the winter and summer seasons.
• In short, they are the general planetary winds which undergo seasonal modifications.
• Such types of winds are more prevalent in countries like India, Bangladesh, Pakistan, Sri Lanka, the Bay of Bengal, the Arabian sea, China, North Australia, Japan and Southeast Asia.

Also, check the NCERT notes on types of rainfall here.

Tertiary Or Local Winds

Apart from the planetary winds and seasonal winds, several local and regional winds are developed on a daily basis. These kinds of winds affect the local weather. They are mostly confined to the lower levels of the troposphere and affect small areas. Some of the local winds are discussed below.

Land And Sea Breezes

• During the day, the landmass gets heated up quickly when compared to the adjoining sea or lake. The hot air above the landmass rises and develops a low-pressure area, whereas the sea is cool and has relatively high pressure. This creates a pressure gradient from sea to land and thus the cold air from the sea moves towards the land. This is known as a sea breeze.
• At night, reversal of conditions takes place. The cold air blows from the land (high-pressure area) towards the sea (low-pressure area). This is known as a land breeze.
• Such types of wind cycles take place on a daily basis and are prevalent on the narrow strips along the coasts and lakes.

Read the article on the ocean floor and its features here.

Mountain And Valley Breezes

• Another diurnal cycle of winds is the mountain and valley breeze.
• On sunny days, the mountain slopes get heated up more quickly than the floors of the valley. As a result, the air above the mountain slope rises and relatively low pressure is created over the slope. Thus, the wind begins to flow from the valley (high-pressure area) to the slope (low-pressure area). This is known as the valley breeze.
• In the evenings, the conditions get reversed and high pressure is developed over the mountain slope and low pressure over the valley. Thus the cold arid heavy air blows from mountain to valley and this is known as the mountain breeze.
• The mountain and valley breezes are also known as katabatic and anabatic breezes respectively.

Hot Winds

The winds which are generated by the mechanism of adiabatic heating are known as the hot local winds. Following are some of the examples of hot local winds that are prevalent in different parts of the world.

Check the article on pressure belts of India here.

Cold Winds

The winds which are dust-laden and have temperatures below the freezing point are known as cold local winds. Following are some of the examples of cold local winds that are prevalent in different parts of the world.

Also, check the NCERT notes on earthquakes here.

Measuring of Wind

The wind, a whisper or a mighty roar, is more than just air in motion. It has a parameter, defined by both its speed and direction. To understand this enigmatic character, there are two tools: anemometers and wind vanes.

Anemometers: These devices are the speedometers of the wind world. Imagine, if you will, a spinning cup or a dancing feather responding to the wind's every whim. That's the essence of an anemometer, capturing the wind's pace in units like miles per hour or knots. Different types, like the classic cup anemometer or the high-tech laser doppler, cater to various needs and environments.

Wind vanes: Ever seen a weathercock perched atop a building, faithfully pointing with its arrow? That's a wind vane, the whisperer of direction. It motions with the wind, its arrow aligning with the source of the breeze, be it a gentle north wind or a blustery west wind.

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