Pressure Winds Storms and Cyclones — Question 11

(i) During the rainy season, when land gets heated in hot, humid, and tropical regions of India, the warm and moist air being lighter rises, thus creating a low-pressure area. Cooler air from surrounding high-pressure areas flows to take its place. This air again gets heated and rises, thereby resulting in a continuous process of wind circulation. As the rising air expands, it cools and moisture in it condenses to form water droplets forming clouds. The water droplets merge to form heavier drops, which come down as rain, hail, or snow. The strong winds accompanied by rain are called a storm. (ii) During a storm formation, under certain conditions, warm air rises to great heights, and the low temperature there changes water droplets into ice particles. Strong winds blowing upwards and downwards result in rubbing between water droplets and ice particles. This generates electric charges within clouds. Ice particles are positively charged, and they move upwards in the upper part of the clouds. Water droplets are negatively charged and occupy the lower part of the clouds. When negatively charged water droplets in the lower part of the cloud move closer to the ground, trees, buildings, and the ground become positively charged. Normally, air acts as an electrical insulator and does not let opposite charges meet. This insulating property of the air breaks down when the build-up charges becomes very large. A sudden flow of charges takes place, resulting in a bright flash of light called lightning. Lightning can occur as opposite charges collide within a cloud, between clouds, or between clouds and the ground. Lightning rapidly heats the air around it. This results in expansion of air to produce a loud sound called thunder. A storm accompanied by lightning and thunder is called a thunderstorm.