Winds, Storm and Cyclones
Science Class Seven
Uneven Heating on Earth
Wind Currents Are Generated Due to Uneven Heating on the Earth
Equator is an imaginary line that divides the earth into two parts. The latitude of the equator is considered as 0o.
Regions near the equator get more sun shining throughout the year. Because of heat the air above the equatorial regions gets warmer and rises up in the air creating a low pressure zone. To fulfill the gap in the low-pressure zone colder air from 30o latitude on either side of the equator rush towards the equator. This cycle continues and wind from 30o north and 30o south latitudes blow towards equator.
On the other hand, air over Polar Regions is colder than the air near 60o latitude. So, air near 60o latitude is warmer and rises up in the air creating a low pressure zone, to maintain the pressure air from Polar Regions rush towards the 60o latitude. This cycle continues and air flows from Polar Regions to 60o latitude.
In this way we can see that wind moves from one area to another due to uneven heating of the earth.
Apart from differential heating, another factor is important for wind movements. This is called the Coriolis Effect. The Coriolis Effect takes place because of the rotation of the earth around its axis. As the earth rotates from west to east, air flows from east to west, in both hemispheres. The figure given below shows wind movements in both hemispheres of the earth.
Uneven Heating on Land and Water
Air flows between land and water also because of uneven heating.
Land becomes warm faster than water.
In summer, near the equator the temperature is high most of the time. Because of high temperature land near the equator gets heated faster than the water in the ocean. As land gets warmed faster, the air above the land areas also gets warmed. The warmer air rises up creating a low pressure zone. To fulfill this gap colder air from the ocean/sea or other bigger water sources rush towards the land. This process continues and air blows from water to land.
In the winter, the direction of the wind gets reversed. It starts flowing from land to the ocean.
Sea Breeze and Land Breeze
Sea Breeze
You have read about the land and sea breezes. In coastal areas land heats up faster than water. The hot air on land moves up, leaving an area of low pressure. To fill these gaps cool air moves from the sea to the land areas. As a result, the wind starts blowing from the ocean to land and, is called the sea breeze. People who live in coastal areas prefer sea facing houses so that they can enjoy the sea breeze because of this reason.
Land Breeze
During the night, in coastal areas the land cools faster than water. This makes air over water warmer than that of over land areas. As warmer air over the water moves up creating a gap. To fulfill this gap, the colder air from land areas starts moving toward the water. This cycle continues and creates the flow of wind from land to ocean or sea or large water bodies. This is called land breeze.
Monsoon
The word 'Monsoon' came from the Arabic word 'Mausam' which means season. Still in India, the word 'Mausam' is used for the season.
As we know, in the summer, most of the time the temperature of land is higher than that of the ocean. Because of getting more heat air above the land gets lighter and rises up leaving a gap over the land. To fulfill this gap air from the ocean rushes towards land. This is similar to the sea breeze.
The air above the ocean is full of moisture, so after reaching over the land moisture gets vaporised and rises up. This cycle continues and a cloud is formed.
This is called "Monsoon Winds".
Thus, "Monsoon Winds" brings rain.
Direction of "Monsoon Wind"
In India, in summer, "Monsoon Winds" came because of uneven heating of land, especially in the hot desert of the State of Rajasthan. The "Monsoon Winds" from Southwest direction.
Country like India depends on rain for agriculture, so "Monsoon" is very important.
In India "Monsoon" comes in the month of June.
In the winter, because of uneven heating of land and water winds are generated from the Northwest direction from colder land.
These winds have less moisture, so carry less rain.
Monsoon and Happiness
Country like India depends on rain for agriculture, so "Monsoon" is very important.
So, "Monsoon Winds" bring happiness. Farmers wait for "Monsoon". With the starting of rain, the process of agriculture is started.
There are many songs and poems associated with "Monsoon".
Monsoon and Sorrow
Monsoon does not bring happiness always. There are other consequences of monsoon also.
Sometimes more rain causes floods. And flood disturbs life. Many times flood becomes devastating. This poses threats to humans, animals, and plant life.
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