class 7th lesson number 8 Winds Storms and cyclones essay
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Air: Air is a mixture of gases.
Wind: Moving air is called wind.
Air exerts pressure: The fact that Air exerts pressure can be understood by many examples.
Tube of bicycle gets inflated when air is filled in it. This happens because air exerts pressure.
It is difficult to move the bicycle against the direction of wind. Similarly, a sailor feels it difficult to sail his boat against the direction of wind. This happens because air exerts pressure.
When boiled water is filled in a tin can and its mouth is closed with the lid; followed by cold water being poured over it, the can gets distorted. This happens because air inside the can gets condensed and creates low pressure. The higher pressure from outside distorts the shape of the can.
You can fly a kite because air exerts pressure from the rear portion of the kite.
Aeroplane can fly because air exerts pressure.
Birds can fly because air exerts pressure.
High speed wind creates area of low air pressure:
Thatched roof is blown off because of high speed wind. This happens because high speed wind creates an area of low pressure. Due to this, the thatched roof is sucked up and finally gets blown away. Thus, increase in wind speed is associated by decrease in air pressure.
Movement of air:
Air moves from high pressure zone to low pressure zone of air. Air; from high pressure zone; rushes towards the low pressure zone; to fill the gap. Thus, greater is the pressure difference greater will be the speed of wind and vice-versa.
Cause of Wind Movement:
Pressure difference in the air is cause by differential heating. Warm air rises up because it becomes lighter. This creates an area of low pressure below the rising air. The area of low pressure is quickly filled in by cooler air from around. That is how the wind movement is created on the earth. Thus differential heating of air creates pressure difference; which makes the wind movement.
Movement of Air Because of Uneven Heating on Earth:
Movement of Air in Equatorial Region: The Equatorial region gets the highest amount of sunshine throughout the year. Due to this, the air near the equatorial region gets heated. The warm air rises up and creates an area of low pressure. The cooler air; from the higher latitudes; rushes towards the equator to fill the gap. This results in the wind movement from tropical zones towards the equator. Similarly, wind movement is caused in other parts of earth.
Movement of Air Because of Uneven Heating of Land and Water:
Sea Breeze: In coastal areas, the land warms up faster than the ocean surface. Warm air from the land rises up and creates an area of low pressure near the ground. The low pressure zone is filled in by cooler air from the ocean surface. This gives rise to the sea breeze.
Land Breeze: During night, the land cools down faster than the ocean surface. The warmer air from the ocean surface rises up and creates an area of low pressure near the surface. This is filled in by cooler air from the land. This gives rise to the land breeze.
Monsoon: The flow of moist air from ocean towards land in summer is called Monsoon or Monsoon wind. The word Monsoon came from Arabic word ‘mausim’, which means weather. The term ‘Monsoon’ had traditionally been used to describe the typical climate of the Indian Peninsula during the rainy season. Now-a-days, the term ‘Monsoon’ is being also used to describe the similar climate in other parts of the world.
Monsoon winds carry water vapour which falls over the land in the form of rain after cooling down. In India, the harvest depends on the monsoon wind because it is the major factor towards bringing rainfall in India.
Thunderstorm: Many a times, rain is associated with lightning. Rain with lightning is called thunderstorm. This happens mostly in the summer. Thunderstorm occurs frequently in hot and humid tropical areas, such as India.
In summer, the air rises up along with lot of moisture. After rising up to a certain height water vapour cools down and starts coming down in the form of water droplets. The swift drifting of water droplets creates electricity among clouds. This manifests in the form of lighting and sound. This is known as thunderstorm.
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Winds, Storms and Cyclones
Air Pressure
The pressure exerted by air on all bodies at all times in all directions is called air pressure.
Air Pressure
The pressure exerted by air on all bodies at all times in all directions is called air pressure. When air moves at high speeds, it creates a low pressure area. The air inside a balloon exerts pressure in all directions, and makes it blow up. Air opposes the motion of a moving object. This is called air resistance. That is why you have to exert yourself and pedal hard when you ride a bicycle. Another example in which air pressure can be observed: Take a glass and fill only 1/3 of it with water. Cover the mouth of the glass with an index card. Now hold the card in place and invert the glass over a sink and remove your hand from the card. The card sticks to the glass. This is due to air pressure. The air outside exerts an upward pressure on the index card. This air pressure is more than the weight of the water in the glass.
Winds
Winds are caused by variations in air pressure. A wind blows from a region of high pressure to a region of low pressure. The speed of the wind mainly depends on the difference between the pressures of the air in the two regions.
High speed winds are known to blow away thatched and tiled roofs in rural and semi-urban areas. Strong winds can uproot trees and electric poles, and even snap cables.
Anemometer
The instrument used to measure the speed of wind is called the anemometer. It is usually fixed on the top of a building.
Winds
Air expands on heating,and the expanded air pushes for more space.
Air expands on heating, and the expanded air pushes for more space.
Monsoon Winds
The word monsoon is derived from the Arabic word "mausam," which means season. The winds from the ocean carry water in the form of vapours, resulting rains over land. These are called monsoon winds.
Thunderstorms
A storm with lightning and thunder is called a thunderstorm. It occurs due to the convection of air in hot and humid areas.
Cyclone
A natural calamity caused by difference in air pressure in the atmosphere is called a cyclone. A cyclone is a violently rotating windstorm. Cyclones are dangerous. Cyclones begin as thunderstorms.
In tropical regions like India, thunderstorms are common, but very few thunderstorms convert into cyclones. In India, the eastern coast is more vulnerable to cyclones than the western coast.
In different parts of the world, cyclones are known differently. For example, in America, a cyclone is referred to as a hurricane, while the Filipinos and Japanese called it a typhoon.
The largest tropical cyclone recorded was Typhoon Tip that struck Japan in 1979. At its peak strength, the diameter of its eye wall was 2220 kilometres. The wind speeds were recorded at 305 kilometres per hour.
Formation of Cyclones
The formation of a cyclone depends on the speed and direction of the wind, temperature and humidity. A cyclone also arises:
Due to the difference in the temperatures of the two regions.
A low pressure is created as the air in the high temperature region becomes warm and rises.
The gap in the low pressure area is filled by cold air rushing in from the surrounding areas.
When the warm air arises, it cools, condenses and forms clouds.
When the water vapour in the clouds turns into raindrops, the heat possessed by the water vapour is released into the atmosphere.
The process repeats and the release of heat from the water vapour continues.
During a thunderstorm, do not:
Rest under a tree
Take shelter under an umbrella with a metallic end
Lie down flat, if in an open place
Sit near a window
Eye of a Cyclone
The calm and clear area at the centre of a cyclone is called the eye of the cyclone.
Tornado
A rotating column of high speed winds that appears as a dark funnel-shaped cloud reaching from the ground to the sky is called a tornado. A tornado may form within a cyclone. A tornado forms due to the effect of low pressure in the eye of a cyclone. Objects near the base of a tornado, such as cars, dust, debris and even houses, are sucked into its funnel and thrown out at the top.
More than a thousand tornadoes occur every year across the world. Most occur in the United States. Tornadoes occur regularly in the regions around the Atlantic Ocean. Weak tornadoes travel with wind speeds of 50 to 60 km/hr, while a violent tornado can travel at a speed of about 400 km/hr. A tornado is a natural disaster, but not as dangerous as a cyclone.
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