My Science School

          The formation of clouds has always been very important to man. You must be curious to know how the clouds are formed and how many kinds of clouds are there.

          We know that the water of rivers, ponds, lakes and seas is converted into vapour by the solar heat and this vapour moves in air. Hot air, mixed with water vapour, being lighter, goes up high in the sky. When the air mixed with water vapour accumulates at one place, it gives the appearance of smoke. We call it a cloud. 

          On the basis of their different shapes and sizes, clouds have been divided into mainly four kinds:

1. Cirrus clouds: Cirrus clouds are formed at great heights. They are white in colour and look like birds’ feathers. Their height ranges from 8,000 to 11,000 metres. They are made up of small ice particles.

 

 

 

2. Stratus clouds: Stratus clouds are formed at a height of about 2,438 metres. They look like layers of fog. They foretell bad weather and drizzle.

 

Continue reading "How are clouds formed? "

             When wind moves with great speed and creates disturbance in the atmosphere, it is called a storm. Storms of summer are mainly caused by the rise in atmospheric temperature. Due to high temperature, air expands and there is a fall in the atmospheric pressure in that area. To balance it, air from colder regions where there is more pressure, rushes to the hotter regions. Carrying with it a large amount of dust and we call it a dust-storm.

              Tornadoes, cyclones and hurricanes are some of the dangerous storms in which wind makes fast whirling motion. When the temperature of a small area rises to a high degree and, consequently, the atmospheric pressure falls, air from surrounding areas rushes in to fill this vacuum. Because of its fast velocity, wind’s motion in that area becomes whirling. The hot air goes up fast, forming a funnel-shaped cloud. This is called a tornado. The pressure inside a tornado is so low that any object coming in its way gets sucked in. Wind velocity of a tornado goes up to 200 kilometres per hour.

 

               Hurricanes generally belong to tropical areas. They engulf areas within a radius of 80 to 320 kilometers and the wind-speed goes up to 120 to 200 km per hour. The central portion of the hurricane extending from 5 to 15 kilometers is completely calm. This is called the eye of the hurricane. When this portion reaches a particular area the air there comes to a standstill: This gives the impression that the hurricane is over. But, as soon as it leaves the area, it is followed by strong gusts of wind. Since hurricane also is a kind of whirling storm, it advances with a very fast whirling motion. It is called typhoon in east India and in the areas adjoining the Chinese Sea.

 

                The cyclone is also a very dangerous storm. It devastates very large areas. It is caused by the rush of air towards low-pressure areas resulting in large-scale destruction. The violent cyclone which hit East Pakistan (now Bangladesh) on November 13-14, 1970 claimed lives of one million people.

 

             Occasionally, you must have seen, some round balls of ice accompanying heavy rains. These round balls are called hails. They are seen more often in summer than in winter. Hailstones are of varying sizes. You may be curious to know how hails are formed in the atmosphere!

              When raindrops start falling from the clouds towards the Earth, sometimes they have to pass through very cold regions and due to this low temperature, these raindrops get frozen. These frozen raindrops are called snow flakes. Sometimes these snow flakes are lifted up by strong winds to regions already having raindrops. As a consequence they get stuck to these snow flakes. When they fall through colder regions of the atmosphere, they are again frozen. This way the size of the frozen raindrops goes on increasing. When the weight of these frozen drops is more than the up thrust of the air, they fall down on the Earth in the form of hailstones.

            If you cut a hailstone into slices, you will notice many layers of transparent and semi-transparent snow. These layers are formed by the repeated freezing of the water-drops. The diameter of hailstones varies from 1 cm to 8 cm. A hailstone may weigh even more than half a kilogram. On 6 July, 1928, a very big hailstone fell at a place named Potter, Nebraska. It weighed 717 gm and had a diameter of 15 cm.

            Hailstones can cause extensive damage. It has been observed that some animals and human beings have even succumbed to the injuries caused by hailstones. Hailstones are very damaging to the crops - they destroy the standing crops. On 30th April 1886, 246 people died of injuries caused by hailstones in Moradabad in UP (India).