7th Class Science Winds, Storm and Cyclones Wind, Storms and Cyclones

Wind, Storms and Cyclones

Wind

Moving air is called wind. Wind occurs due to the heating caused by the sun. The unequal heating of different parts of the earth causes the wind to blow. When the wind blows with slow speed it is called breeze. When the wind blows with high speed it is called storm.

Air Pressure

Air exerts pressure. Like temperature and humidity, air pressure also determines the weather of a place on a particular day. Air pressure can be measured with an instrument called barometer.

Wind is Produced Due to Uneven Heating on the Earth by the Sun

Uneven heating on the earth can take place by two situations:

1. Uneven heating between the equator and the poles of the earth

Maximum heat absorbed by the regions close to the equator makes the air warm and this warm air rises creating an area of low pressure. The cooler air from the regions of up to \[30{}^\circ \] latitude belt on both the sides of the equator rushes towards the equator. Again, the air at latitudes of about \[60{}^\circ \] on both sides of the equator is warmer than at the poles. So, the cold air from the poles blows towards the warmer regions up to about \[60{}^\circ \] latitudes.

2. Uneven heating of land and water of oceans

In summer land near the equator heats up faster than the water in oceans. The land air heated and rises by creating a low pressure area. 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. In winters wind blows from the land towards the ocean. Rotation of earth is responsible for making the winds blow in an easterly direction, instead of straight north and south direction.

Cyclones

Cyclone is a type of storm that develops over sea. Cyclone has high speed wind swirling around a low pressure centre. The low pressure centre is called the eye of the cyclone. Cyclone develops mostly over tropical sea. The sunlight heated the air that creates the area of low pressure. Cold air moves into the area pushing the hot air in the upward direction. This pushing of hot air by cold air from the surrounding areas continues and thus creates a cycle or current of air. The rotation of the earth drags air current around the low pressure area. In this way, the wind swirls around the centre. The wind swirls anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Cyclones that develop over western Atlantic and eastern Pacific Ocean are called hurricanes. Cyclones that develop over western Pacific are called typhoons. Cyclones that develop over Indian Ocean, Bay of Bengal and Arabian Sea are called cyclones. Cyclones affect India in the months of April and May and then again between October and December.