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.
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