Chapter - 8 Winds, Storms and Cyclones

·      Air around us exerts pressure.

·      Air expands on heating and contracts on cooling.

·      Warm air rises up, whereas comparatively cooler air tends to sink towards the earth’s surface.

·      As warm air rises, air pressure at that place is reduced and the cooler air moves to that place.

·      The moving air is called wind.

·      Uneven heating on the earth is the main cause of wind movements.

·      Winds carrying water vapor bring rain moving air is called the wind.

·      Air moves from the region where the air pressure is high to the region where the pressure is low. The greater the difference in low pressure, the faster the air moves.

·      On heating the air expands and occupies more space. When the same thing occupies more space, it becomes lighter. The warm air is therefore, lighter than the cold air. That is the reason that the smoke goes up. In nature there are several situations, where warm air rises at a place. The air pressure at that place is lowered. The cold air from the surrounding areas rushes in to fill its place. This sets up convection in air.

·      Wind speed plays an important role in the formation of storms. It is, therefore, important to measure the wind speed. The instrument that measures the wind speed is called an anemometer.

Uneven heating between the equator and the poles

Regions close to the equator get maximum heat from the Sun. The air in these regions gets warm. The warm air rises, and the cooler air from the regions in the 0–30 degrees latitude belt on either side of the equator moves in. These winds blow from the north and the 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 and the cold wind from the polar regions rushes in, to take its place. In this way, wind circulation is set up from the poles to the warmer latitudes.

Uneven heating of land and water

In summer, near the equator the land warms up faster and most of the time the temperature of the land is higher than that of water in the oceans. The air over the land gets heated and rises. This causes the winds to flow from the oceans towards the land. These are monsoon winds.  In winter, the direction of the wind flow gets reversed; it flows from the land to the ocean.

THUNDERSTORMS AND CYCLONES

Thunderstorms develop in hot, humid tropical areas like India very frequently. The rising temperatures produce strong upward rising winds. These winds carry water droplets upwards, where they freeze, and fall down again. The swift movement of the falling water droplets along with the rising air creates lightning and sound. It is this event that we call a thunderstorm.

If a storm is accompanied by lightning, we must take the following precautions:

ü Do not take shelter under an isolated tree.

ü If you are in a forest take shelter under a small tree.

ü Do not lie on the ground.

ü Do not take shelter under an umbrella with a metallic end.

ü Do not sit near a window. Open garages, storage sheds, metal sheds are not safe places to take shelter.

ü A car or a bus is a safe place to take shelter.

ü If you are in water, get out and go inside a building.

Structure of a cyclone

The center of a cyclone is a calm area. It is called the eye of the storm. A large y cyclone is a violently rotating mass of air in the atmosphere, 10 to 15 km high. The diameter of the eye varies from 10 to 30 km. It is a region free of clouds and has light winds. Around this calm and clear eye, there is a cloud region of about 150 km in size. In this region there are high-speed winds (150–250 km/h) and thick clouds with heavy rain. Away from this region the wind speed gradually decreases. The formation of a cyclone is a very complex process.

CYCLONE

Before cloud formation, water takes up heat from the atmosphere to change into vapor. When water vapor changes back to liquid form as raindrops, this heat is released to the atmosphere. The heat released to the atmosphere warms the air around. The air tends to rise and causes a drop in pressure. More air rushes to the center of the storm. This cycle is repeated. The chain of events ends with the formation of a very low-pressure system with very high-speed winds revolving around it. It is this weather condition that we call a cyclone. Factors like wind speed, wind direction, temperature and humidity contribute to the development of cyclones. Cyclones can be very destructive. Strong winds push water towards the shore even if the storm is hundreds of kilometers away. These are the first indications of an approaching cyclone. The water waves produced by the wind are so powerful that a person cannot overcome them. The low pressure in the eye lifts water surface in the center. The rising water may be as high as 3–12 meters. It appears like a water-wall moving towards the shore. As a result, the seawater enters the low-lying coastal areas, causing severe loss of life and property. It also reduces the fertility of the soil. Continuous heavy rainfall may further worsen the flood situation. High-speed winds accompanying a cyclone can damage houses, telephones and other communication systems, trees, etc., causing tremendous loss of life and property.

Tornadoes:

 A tornado is a dark funnel shaped cloud that reaches from the sky to the ground. Most of the tornadoes are weak. A violent tornado can travel at speeds of about 300 km/h. Tornadoes may form within cyclones. The whole coastline of India is vulnerable to cyclones, particularly the east coast. The west coast of India is less vulnerable to cyclonic storms both in terms of intensity and frequency of the cyclones.

EFFECTIVE SAFETY MEASURESES ƒ

ü A cyclone forecast and warning service.

ü Rapid communication of warnings to the Government agencies, the ports, fishermen, ships and to the general public.

ü Construction of cyclone shelters in the cyclone prone areas, and Administrative arrangements for moving people fast to safer places.

ü Action on the part of the of people: We should not ignore the warnings issued by the meteorological department through TV, radio, or newspapers. ƒ

ü We should — make necessary arrangements to shift the essential household goods, domestic animals and vehicles, etc. to safer places;

ü avoid driving on roads through standing water, as floods may have damaged the roads;

ü and keep ready the phone numbers of all emergency services like police, fire brigade, and medical centers.

ü Some other precautions, if you are staying in a cyclone hit area -Do not drink water that could be contaminated. Always store drinking water for emergencies. Do not touch wet switches and fallen power lines. Do not go out just for the sake of fun. Do not pressurize the rescue force by making undue demands. Cooperate and help your neighbors and friends.