Thunderstorms and cyclones

Thunderstorms develop in hot, humid tropical areas like India very frequently.The rising temperatures produce strongupward rising winds. These winds carry

water droplets upwards, where theyfreeze, and fall down again. The swift

movement of the falling water dropletsalong with the rising air create lightningand sound. It is this event that we call a

thunderstorm.

Precautions against lighting storms1. Do not take shelter under an

isolated tree. If you are in a foresttake shelter under a small tree. Do

not lie on the ground.2. Do not take shelter under anumbrella with a metallic end.

3. Do not sit near a window. Opengarages, storage sheds, metal

sheds are not safe places to takeshelter.

4. A car or a bus is a safe place totake shelter.

5. If you are in water, get out and goinside a building.

Structure of a cycloneThe centre of a cyclone is a calm area.It is called the eye of the storm. A largecyclone is a violently rotating mass of

air in the atmosphere, 10 to 15 kmhigh. The diameter of the eye varies

from 10 to 30 km .It is aregion free of clouds and has light

winds. Around this calm and clear eye, there is a cloud region of

about 150 km in size. In this regionthere are high-speed winds (150–250

km/h) and thick clouds with heavyrain. Away from this region the wind

speed gradually decreases. Theformation of a cyclone is a very

complex process.

How a thunderstorm become a cycloneCloud formation, water takes

up heat from the atmosphere to changeinto vapour. When water vapour changes

back to liquid form as raindrops, thisheat is released to the atmosphere. Theheat released to the atmosphere warmsthe air around. The air tends to rise and

causes a drop in pressure. More airrushes to the centre of the storm. Thiscycle is repeated. The chain of events

ends with the formation of a verylow-pressure system with very

high-speed winds revolving around it.It is this weather condition that we call

a cyclone. Factors like wind speed,wind direction, temperature and

humidity contribute to the developmentof cyclones.

Destruction caused by cycloneCyclones can be very destructive.

Strong winds push water towards theshore even if the storm is hundreds ofkilometres away. These are the first

indications of an approaching cyclone.The water waves produced by the windare so powerful that a person cannot

overcome them.The low pressure in the eye lifts

water surface in the centre. The risingwater may be as high as 3–12 metres

Fig. 8.11 Formation of a cyclone(Fig. 8.13). It appears like a water-wallmoving towards the shore. As a result,

the seawater enters the low-lying coastalareas, causing severe loss of life and

property. It also reduces the fertility ofthe soil.

.

Continuous heavy rainfall may further worsen the flood situation. High-speed winds accompanying

a cyclone can damage houses,

telephones and other communication

systems, trees, etc., causing

tremendous loss oflife and property.

Cyclone

A cyclone is known bydifferent names in different

parts of the world. It iscalled a ‘hurricane’ in the

American continent. InPhilippines and Japan it

is called a ‘typhoon’

TornadoesTornadoes: In our country

they are not very frequent. Atornado is a dark funnel

shaped cloud that reachesfrom the sky to the ground

Most of thetornadoes are weak. A violenttornado can travel at speeds

of about 300 km/h.Tornadoes may form within

cyclones.The whole coastline ofIndia is vulnerable to

cyclones, particularly theeast coast. The west coast of

India is less vulnerable tocyclonic storms both interms of intensity and

frequency of the cyclones.

Action On The Part of PeopleWe should not ignore the warnings

issued by the meteorologicaldepartment through TV, radio, or

newspapers. We should —make necessary arrangements to

shift the essential household goods,domestic animals and vehicles, etc.

to safer places;avoid driving on roads through

standing water, as floods may havedamaged the roads; and

keep ready the phone numbers of allemergency services like police, fire

brigade, and medical centres.

Anemometerall storms are low-pressuresystems. Wind speed plays

an important role in the formation ofstorms. It is, therefore, important to

measure the wind speed. Theinstrument that measures the wind

speed is called an anemometer.