Air around us is always moving. Sometimes it moves gently as a breeze, and sometimes it rushes violently as a storm or cyclone. The moving air is called wind. In this chapter we study what causes winds, how storms are formed, what cyclones are, and how we can protect ourselves from them. Wind plays an important role in our weather and climate, and understanding it helps us stay safe during disasters.
Wind is moving air. We cannot see air, but we can feel it moving. Air exerts pressure, and when air moves from a region of high pressure to a region of low pressure, wind is created. The greater the difference in air pressure between two regions, the faster the wind blows. Strong winds are dangerous and can uproot trees, damage houses and cause huge loss of life and property. That is why accurate weather forecasting and warnings are very important.
Air pressure is the pressure exerted by the weight of air on everything around us. Air pressure is the highest at sea level because the entire column of air above us presses down. As we go higher, the air pressure decreases. Wind is caused by the difference in air pressure between two regions; air always moves from an area of high pressure to an area of low pressure.
We can observe this in our daily life. When air in a closed bottle is heated, it expands and pushes against the walls of the bottle, increasing the pressure inside. If a lid is tightened on a plastic bottle and the bottle is heated, the air inside expands and the pressure increases. Similarly, a balloon expands when air is blown into it because the pressure of the air inside becomes greater than the air pressure outside. Changes in air pressure help us predict the weather; a sudden drop in atmospheric pressure often indicates the arrival of a storm or cyclone.
A thunderstorm is a storm with lightning and thunder, accompanied by heavy rain, strong winds and sometimes hail. Thunderstorms develop when warm, moist air rises rapidly, expands and cools, forming clouds called cumulonimbus clouds. The rapid rising of hot air creates a low-pressure area below, and air from surrounding areas rushes in, causing strong winds. During a thunderstorm, an electric discharge happens between clouds or between clouds and the ground, which we see as lightning and hear as thunder.
A cyclone is a violent storm with very high-speed winds rotating around a low-pressure centre. Cyclones are called by different names in different parts of the world - 'typhoon' in China and Japan, 'hurricane' in America, and 'cyclone' in India. Cyclones form over warm ocean waters when the sea surface temperature is high. The warm, moist air rises, creating a low-pressure area, and the surrounding air rushes in rapidly. Due to the Earth's rotation, this incoming air rotates, forming the spinning storm. The centre of the cyclone is called the eye, where the weather is calm. Cyclones bring heavy rainfall, strong winds and storm surges, which cause flooding and massive destruction along the coast.
A cyclone forms in stages over warm oceans. First, the ocean water must be warm (above 26°C), so that large amounts of water vapour evaporate. As this warm, moist air rises, it creates a low-pressure area near the surface. The air from the surrounding high-pressure areas rushes in toward the low-pressure centre, carrying more moisture. Due to the rotation of the Earth, this air spirals inward, and the storm grows in strength. When the wind speed becomes very high, the system is called a cyclone.
The whole process involves continuous condensation of water vapour, which releases heat and drives the storm. The centre of the cyclone, called the eye, is calm and has clear skies, while the strongest winds and rains occur in the wall around the eye. Cyclones weaken when they move over land because they are cut off from the warm ocean water that provides their energy. That is why the destruction is usually greatest near the coast and reduces inland.
Cyclones are destructive, but their effects can be minimised by taking proper precautions. Advance warnings given by the meteorological department help people move to safer places before the cyclone arrives. People living in coastal areas should listen to radio and television warnings and move to cyclone shelters or safer buildings. During a cyclone, people should remain indoors, away from windows and doors, and avoid going out in the storm.
Governments also take steps to reduce the damage. Trees should not be planted too close to buildings as they may fall during the storm. Strong and elevated cyclone shelters should be built in coastal areas, and early warning systems should be strengthened. Farmers should be informed about cyclones so that they can harvest their crops or move animals to safe places in time. Educational awareness about what to do before, during and after a cyclone can save many lives.
| Weather System | Cause | Effects |
|---|---|---|
| Wind | Air moves from high to low pressure | Carries weather, wind energy |
| Thunderstorm | Rapid rising of warm moist air | Lightning, thunder, heavy rain |
| Cyclone | Low-pressure centre over warm ocean | High winds, heavy rain, storm surge |
| Name of Cyclone | Region |
|---|---|
| Cyclone | India and Indian Ocean |
| Hurricane | America (Atlantic) |
| Typhoon | China and Japan (Pacific) |
Air is all around us and its movement creates winds, which are caused by differences in air pressure. Severe weather systems like thunderstorms and cyclones develop when warm, moist air rises rapidly, and cyclones grow over warm ocean waters with spinning winds around a calm eye. Although cyclones can cause enormous destruction, their effects can be reduced with advance warnings, proper shelters and public awareness. Understanding the science of winds and storms helps us appreciate the power of nature and prepares us to stay safe during natural disasters.