Let us learn about monsoon winds. You might have learned in geography that regions close to the equator get maximum heat from the sun. It means the Earth�s equatorial and tropical regions are hotter than the polar regions. The air in these regions is warmer than the air of polar regions. The warm air rises up creating a low-pressure area in these regions.

 

The cooler air from the regions in the 0 to 30 degrees latitude belt on either side of the equator moves in. The direction of these winds is from north and south towards the equator. At the poles, the air is colder than that at latitudes about 60 degrees. The warm air at these latitudes rises up and the cold wind from the polar regions rushes in, to take its place.

 

This results in the convection of air. The warm air from the regions close to the equator rises up and the cold air from the polar regions rushes in, to cover this place. The movement of air due to uneven heating of the earth�s surface between the equator and the poles results in the circulation of wind across the globe. See the wind flow pattern because of uneven heating on the earth.

 

Wind Current �Monsoon Winds

 

You have learned that Monsoon winds are produced due to uneven heating of land & water. Monsoon winds from the sea carry water & bring rain. Monsoons are seasonal rains. Winds from the ocean rise up with water vapors. These water vapors condense from clouds resulting in the rain on the earth. This process is termed Monsoon winds.

 

The word �Monsoon� is derived from the Arabic word Mausam which means season. These monsoons bring a lot of happiness to our life. Farmers in our country depend mainly on rains for their harvest. You must have heard many folk songs associated with clouds & rains.

 

We depend on monsoon rains not only for harvesting but for our drinking water too. You would have heard about the problems related to the late monsoon. No rain results in the condition of no food and no drinking water for us. But excess rain also is not good at all. Rains often create problems. It can sometimes cause disasters and pose threat to humans, animals, and plant life. Flooding due to excessive rainfall may be very dangerous.

 

Wind Currents- Direction

 

You have learned that the warm air from equatorial and tropical regions rises up and the cold wind from the polar regions rushes in to take its place. You must be thinking that the direction of these winds is in a straight line from north to south of the equator.

 

But it is not so. Such winds do not flow exactly in the north-south direction. Their direction of flow is changed by the rotation of the earth on its axis. Winds are also caused by the uneven heating of water and land in coastal areas.

 

You have learned about Land Breeze and Sea Breeze in the chapter heat. You know that the air above land and water in the same region has a different temperature. In summers, the land near the equator warms up faster than the sea and most of the time land�s temperature is higher than that of water in the oceans.

 

The air above the land gets heated and rises up, creating a low-pressure area. Now, the air from the sea which is relatively cooler moves in over the land resulting in wind formation. These are Monsoon winds. The direction of these winds is reversed in winters. They flow from the land to the ocean.

 

Measuring Speed of Wind

 

Many times, you would have experienced light winds and many times strong winds too. Have you ever wondered how to measure the speed of the wind? Here is an instrument that is used to measure the speed of the wind. This is called Anemometer.

 

Generally, it is installed at the top of the buildings. This instrument is designed with three or four small hollow metal hemispheres, set so that they catch the wind and revolve around a vertical rod. An electric device records the revolutions of the cups and calculates the speed of the wind.

 

High-speed wind and Reduced pressure

 

You know that there is air all around us. Air travels from high-pressure systems to low pressure systems.

 

Let us do an activity to understand the relationship between high-speed wind and reduced pressure.

 

Activity: Take two sheets of thick paper and fold them in the shape of funnels. Join them in the shape of funnels. Join them as shown in the figure and insert a straw at the joints.

 

Fix a rubber shower at the free end of the straw. Place a table tennis ball on the table. Now, hold the whole arrangement with rubber just above the ball. Now, blow hard from one side of the funnel. See how the ball is rising up towards the straw. High-speed windblown from your mouth reduces the volume of air in the funnel and creates a low-pressure area.

 

Due to this, the air from the surrounding area rushes in through the straw. This flow of incoming air causes the table tennis ball to rise with it. You would have experienced that when the high-speed wind is blowing, the curtains of your corridor are pulled inward.

 

It happens due to low pressure created by strong winds, the air in the surrounding areas moves in and pulls the curtains inward. Always remember that the increased wind speed is accompanied by reduced air pressure. To understand this, let�s do another activity.

 

Make a paper tent and place it on the table. Now, blow air on this paper tent so that it could fly in the air. Why didn�t this paper fly? Because the air moved out with high speed when you blew under it. And you know that high-speed wind is always accompanied by low pressure, the pressure exerted on the tent by the air above it, flattened it.

 

Can you imagine what would happen if the high-speed wind blew over the roofs of buildings? If the roofs were weak, they could be lifted and blown away. This generally happens in the case of thatched roofs.

 

Read More- What is Thunderstorm? Definition and Precaution - Science Class 7