Contents
Physics Topics cover a broad range of concepts that are essential to understanding the natural world.
What is Wind ? How Wind is Produced ?
Wind is the movement of air which depends on the difference in air pressures (or atmospheric pressures) in the two regions. Air moves (or flows) from the regions of high air pressure to regions of low air pressure in the atmosphere. The greater the difference in air pressure, the faster the air moves.
Thus, the speed of wind depends on the difference in air pressures between the two regions. The greater the difference in air pressures between two regions, the faster the wind blows. The differences in air pressures (or atmospheric pressures) in different regions of the earth which cause wind to blow are created in nature due to the uneven heating (or unequal heating) on the earth in these regions.
Thus, uneven heating on the earth in different regions is the main cause of wind movements. So, in order to understand how winds are produced, we should first know which regions (or areas) of earth get more heat from the sun and which regions of earth receive less heat from the sun leading to an unequal heating on the earth. This is discussed below.
The equator of earth is at the minimum distance from the sun (see Figure), so the region around the equator of earth (called equatorial region) gets the maximum heat from the sun and hence it is very hot. As a region gets more and more away from the equator (towards the poles), the amount of suns heat received by the region goes on decreasing gradually leading to less hot climates (or cooler climates).
The poles of the earth (north pole and south pole) are at the maximum distance from the sun and hence get the minimum heat from the sun. So, the polar regions of the earth are very cold.
The angular distance of a place (or region) north or south of the earth’s equator is represented by ‘latitude’ (which is measured in degrees). Equator of earth has 0° latitude (zero degree latitude); North pole of earth has 90°N latitude (90 degrees North latitude); whereas South pole of earth has 90°S latitude (90 degrees South latitude) (see Figure).
A latitude of 30°N (30 degrees North) means a place on the earth’s surface which is 30 degrees North of equator. A latitude of 60°N (60 degrees North) means a place which is 60 degrees North of equator. A latitude of 30°S (30 degrees South) means a place which is 30 degrees South of equator. Similarly, a latitude of 60°S (60 degrees South) means a place which is 60 degrees South of the equator. Keeping these points in mind, we will now describe how winds are produced (or generated) in nature.
Wind Is Produced Due To Uneven Heating On The Earth By The Sun
Wind blows due to the difference in the air pressures (or atmospheric pressures) in the two regions. These differences in air pressures are created by the uneven heating (unequal heating) on the earth in the two regions. So, we can now say that : Wind is produced due to uneven heating on the earth by the sun. The uneven heating on the earth (which produces winds) can take place under two situations :
- Uneven heating between the equator and poles of the earth, and
- Uneven heating of land and water of oceans.
We will now describe how wind is produced in both these situations, one by one.
1. Wind is Produced by the Uneven Heating Between Equator and Poles of Earth
The regions close to the equator of earth get the maximum heat from the sun, so the air in equatorial regions gets heated and becomes warm (see Figure). The warm air rises in the equatorial regions of earth creating an area of low air pressure.
The cooler air from the regions of up to 30 degrees latitude belt on both the sides of the equator (being at higher pressure), rushes towards the equator to take the place of warm, rising air. This makes the wind to blow from the north and south directions towards the equator (see Figure).
Again, the air at latitudes of about 60 degrees on both sides of the equator is warmer than at the poles (which is very cold). So, the warmer air at about 60 degrees latitudes rises up creating regions of low air pressure and cold air from the polar regions (being at higher pressure) rushes in to take its place.
This makes the winds blow from the poles of the earth towards the warmer regions up to about 60 degrees latitudes. These winds also blow from the north and south directions towards the warmer latitude regions (see Figure).
Please note that the winds shown in Figure 8 (by the arrows) are not blowing in the exact north-south direction? The winds produced by the uneven heating on the earth between the equator and the poles would have blown in the exactly north- south direction (from ‘north to south’ or from ‘south to north’) if the earth did not rotate on its axis.
The winds produced by the uneven heating of the earth between the equator and the poles do not blow in the exact north-south direction because a change in the direction of winds is caused by the rotation of the earth on its axis (see Figure).
2. Wind is Produced by the Uneven Heating of Land and Water in Oceans
In summer, land near the equator of earth heats up faster than the water in oceans, so most of the time, the temperature of land is higher than that of water in oceans. The air over the land gets heated and rises creating a low pressure area. The cooler air from over the oceans (being at higher pressure), rushes towards the land. This causes the wind to blow from the oceans towards the land.
The winds blowing from the oceans towards the land in summer are called monsoon winds. The monsoon winds carry a lot of water from the oceans (in the form of water vapour) and bring large amount of rains on land. The process in which the winds coming from the oceans carry a lot of water vapour and bring rains is a part of the ‘water cycle’ in nature.
In India, the land (especially the Rajasthan desert) gets heated much more in summer than the water in the Indian ocean. This uneven heating of ‘land’ and ‘water in Indian ocean’ during summer, generates monsoon winds from the Indian ocean.
The monsoon winds coming from the south-west direction in summer carry a lot of water vapour from the Indian ocean and bring heavy rains (known as ‘monsoon’ or ‘rainy season’) [see Figure (a)], The summer monsoon is very important to the farmers in our country because most of the annual rainfall occurs at this time and helps in growing crops. Many farmers in our country depend mainly on rains for the irrigation of their crops.
We have just learnt that during summer, wind blows from the oceans towards land. In winter, the direction of wind flow gets reversed. During winter, wind blows from the land towards the ocean. This happens as follows: During winter, land cools down faster than the water in oceans. So, the temperature of water in oceans is higher than that of land.
The warm air over the oceans rises up creating a region of low pressure and cooler air from the land rushes towards the ocean. This causes wind to blow from land towards the oceans. The winds coming from colder land regions (or colder winds) carry only a little of water vapour and hence bring only a small amount of rain in winter season.
In India, the land (especially the north-west region) gets cooled much more in winter than the water in Indian ocean. This uneven heating of land and water in Indian ocean during winter generates winds from the north-west colder land going towards the Indian ocean [see Figure (b)]. The colder winds coming from the north-west direction in winter carry only a small amount of water vapour and hence bring only a small amount of rain in winter season.