Question 1 What is a thunderstorm? Describe the damages caused by a tornado? What precautions should be taken for protection from a tornado?
Question 2 What is a cyclone? Where is a cyclone formed?
Question 3 Name any five factors which help in the development of a cyclone? What is the centre of cyclone known as?
Question 4 Describe how a cyclone causes widespread destruction leading to a great loss of life and property?
Question 5 State the various precautions to be observed by a person living in a cyclone hit areas?
Question 6 What is a thunderstorm? Explain how thunderstorm is formed?
Question 7 What type of areas are suitable for the frequent development of thunderstorm?
Question 8 State the precautions which should be observed to protect ourselves from lightning during a thunderstorm?
Question 9 Which coast of India is more vulnerable to cyclones?
- 1 Thunderstorm
- 2 Precautions To be Taken During a Thunderstorm
- 3 Cyclone
- 4 Effective Safety Measures By the Government
- 5 Action on the Part of People Before a Cyclone Hits Their Area
- 6 Precautions to be Taken After the Cyclone Hits an Area
- 7 Tornado
A storm with thunder and lightning is called thunderstorm. A thunderstorm is accompanied by heavy rains or hail.
Thunderstorms develop in hot and humid tropical areas very frequently. This is because the heat of tropical area warms up the air and makes it rise up, whereas humidity provides the water vapour for the formation of clouds.
The sun heats the surface of earth. The hot surface of earth warms the air in contact with it. The warm air rises up creating a low pressure area. And cool air rushes in to take its place in the form of strong winds. As the warm air rises, it transfers heat to the upper levels of atmosphere and begins to cool.
The water vapour present in the rising air cool and condense to form a cloud. The cloud grows upwards into areas where the temperature is close to the freezing point of water (0°C). Some of the water vapour of cloud forms tiny water droplets and some of it turns into ice particles. The friction between fast rising ‘water droplets’ in the cloud and falling ice particles produces opposite electric charges on them.
Due to this, the top of cloud becomes positively charged and the bottom of cloud becomes negatively charged. When a large amount of opposite electric charges build up in the cloud, a tremendous amount of electric current passes through the air in the cloud which produces a big electric spark within the cloud. This electric spark is the lightning. The spark of lightning heats the nearby air too
This extremely hot air expands explosively causing a loud sound called thunder. When electric charges from the bottom of the electrically charged cloud flow down through the air to the ground, then we see the flash of lightning coming towards the earth. A thunderstorm brings strong winds, thunder, lightning and heavy rains (or hail).
Precautions To be Taken During a Thunderstorm
When lightning strikes the earth, it can kill people. It also damages buildings.
We should take the following precautions during a thunderstorm to protect ourselves from lightning:
(1) We should not sit near a window during lightning. Open garages, storage sheds and metal sheds are also not safe places to take shelter during lightning.
(2) We should not take shelter under an umbrella with a metallic end during lightning. This is because metallic end of umbrella may act as a conductor for lightning and harm us.
(3) We should not take shelter under an isolated and tall tree. This is because an isolated tall tree is more likely to be hit by lightning due to its nearness to the clouds. We should take shelter under a small tree.
(4) A car (or a bus) is a safe place to take shelter during lightning (because its metal body can conduct lightning to earth safely, without harming us).
(5) If we are in water when the thunderstorm begins and lightning takes place, we should get out of water and go inside a building.
A cyclone is a huge revolving storm caused by very high speed winds blowing around a central area of very low pressure in the atmosphere.
A cyclone revolves due to the force exerted by the rotation of earth. The centre of a cyclone is a calm area (having very low air pressure). The centre of cyclone is called the ‘eye’ of the cyclone. The eye of cyclone is a region free of clouds and it has only light winds.
Around the calm and clear eye of cyclone, there is a cloud region of about 150 kilometres in size. In this region, there are very high speed winds (having speeds of 150 km/h to 250 km/h) which are moving in circles around the eye, and thick thunderclouds which produce heavy rain.
Formation of cyclone
Factors like temperature, humidity, wind speed, wind direction and rotation of earth contribute to the development of a cyclone.
(1)The sun heats the sea- water too much during summer. Warm and moist air rises up very rapidly from the hot sea surface. This creates area of very low pressure causing cool air to rush in to fill the vacant space.
(2) As the warm and moist air (containing a lot of water vapour) rises high up in the atmosphere, it gets cooled and the water vapour present in it condenses to form thick clouds (called thunderclouds) releasing a lot of heat in the atmosphere.
(3) The heat released by the condensation of water vapour in the atmosphere warms the air all around. This warm air rises higher into the atmosphere causing a low pressure. More air rushes up to take the place of warm, rising air. This process is repeated again and again making more and more air to rise up higher and higher in the atmosphere, and also forming more and more thick clouds (or thunderclouds) all around.
(4) The constant rotation of earth on its axis exerts a force on the rapidly rising columns of air (or winds). The force exerted by the rotation of earth makes the high speed winds revolve in the form of a spiral moving upwards with a great force and create a tunnel of very low pressure inside it. The swirling winds move faster and faster forming huge circles. This weather condition consisting of a system of high speed winds revolving around a central area of very low pressure is the cyclone. The area of very low pressure at the centre of the cyclone is its eye.
The end of a cyclone comes quickly if a cyclone moves over land because it no longer receives heat energy and moisture from warm sea-water.
A cyclone is known by different names in different parts of the world.
For example: A cyclone is called hurricane in the American continent. A cyclone is called typhoon in Japan and Philippines.
Destruction caused by cyclone
1) The tremendous force of high speed winds accompanying a cyclone can topple trees, electric poles, telephone poles and vehicles, damage houses and hurl people through air, etc., causing a great loss of life and property. The strong winds of cyclone produce powerful water waves in the sea and push sea water towards the shore even if the cyclone is hundreds of kilometres away.
(2) The rising sea water appears like a water- wall moving towards the shore. This water-wall coming from the sea rushes inland with deadly force and causes widespread flooding of low-lying coastal areas. The fast moving flood waters brought in by a cyclone, destroy roads and railway tracks, wash away vehicles, damage houses, drown people and animals and damage crops causing a great loss of life and property. The floods caused by cyclone also reduce the fertility of soil in the cyclone hit areas. This is because the fertile top soil is washed away by flood waters brought in by cyclone.
(3) Cyclones bring with them torrential rains. The continuous heavy rains brought by cyclones may further worsen the flood situation in the area.
(4) The floods caused by cyclones pollute drinking water sources. Drinking of polluted water spreads water-borne diseases (like typhoid and dysentery).
The part of land adjoining the sea (or near the sea) is called coast (or coastal area). The ‘length of coast is called ‘coastline.
The east coast of India is more vulnerable to cyclones. The west coast of India is less vulnerable to cyclones (or cyclonic storms) both in terms of intensity and frequency of cyclones.
Effective Safety Measures By the Government
The following safety measures should be taken by the Government for the people living in cyclone prone coastal areas to prevent cyclone related disasters:
(1) Cyclone shelters should be constructed in cyclone prone coastal areas. Cyclone shelters are strong buildings usually built on pillars which can withstand high speed cyclone winds and where cyclone’s flood water cannot enter.
(2) An efficient cyclone forecast and warning service is essential to prevent cyclone related disasters.
(3)The cyclone warning should be communicated rapidly to the concerned Government agencies, ports ,ships, fishermen and general public living in coastal areas through radio, television, telephones, newspapers and other means.
(4) Government vehicles (such as buses, trucks, etc.) should be kept ready to evacuate people likely to be affected by cyclone from their homes and move them fast to safer places (such as cyclone shelters)
Action on the Part of People Before a Cyclone Hits Their Area
(1) Do not ignore the cyclone warnings issued by the Meteorological Department through newspapers, radio or television.
(2) Make necessary arrangements to shift the essential household goods and domestic animals, etc., to safer place.
(3) Keep ready the telephone numbers of all the emergency services like police, fire brigade and hospitals.
(4) Remain in a state of preparedness to evacuate at short notice when asked to do so by the authorities.
Precautions to be Taken After the Cyclone Hits an Area
(1) Do not drink water that could be contaminated by floods (to avoid water-borne diseases). Drink only clean water which has been stored for emergencies.
(2) Do not touch wet electric switches and fallen electric power lines. Do not use electrical appliances, if wet.
(3) Avoid driving on roads through standing water as floods may have damaged the roads.
(4) Go out only when it is safe to do so.
(5) Do not pressurise the rescue teams by making unnecessary demands. Co-operate with the rescue teams and help your neighbours and friends.
By making use of satellites and radars, a cyclone alert (or cyclone watch) is now issued 48 hours in advance of any expected storm and a cyclone warning is issued 24 hours in advance.
A tornado is a violent storm with a column of rapidly rotating winds, having the appearance of a dark, funnel-shaped cloud that reaches from the sky to the ground .
Before a tornado starts, large thunderclouds appear in the sky. One area of the thundercloud becomes specially dark and dense. The air in this area is rotating quickly. A funnel-shaped cloud begins to form and extend downwards to the ground. The diameter of the narrow end of a tornado (which touches the ground) can be as small as a metre and as large as a kilometre (or even more). Due to very low pressure in it, the funnel of a tornado sucks dust, debris and everything else near its base and throws them out near the top. A tornado moves across the surface of land (or sea) producing very high speed winds.
Destruction Caused by Tornadoes
(1)Tornado uproots trees, electric poles and telephone poles disrupting power supply and telecommunications.
(2)Tornado lifts people and vehicles off the ground and hurls them hundreds of metres away. This causes death of many people and damage to vehicles.
(3) Tornado can cause extensive damage to buildings. When a tornado passes over a building, it sucks up air from around the building.
Protection from a Tornado
The following precautions should be taken for protection during a tornado.
(1) Take shelter in a room situated deep inside the house having no windows or in a basement (underground room).
(2) Shut all the doors and windows of the house and take shelter under a sturdy table .Bend down on your knees and protect your head and neck using your arms.
(3) If a person is in a vehicle when a tornado begins, he should get out of the vehicle, go to a ditch or low-lying area and lie flat in it.
(4) Stay away from fallen electric wires and stay out of damaged areas.