Air & Wind
- Moving air is called wind
- Warm air is lighter than cold air
- The pressure exerted by the atmosphere
- Air moves from the region of higher air pressure to a region of lower air pressure
- When warm air rises at a place, the air pressure is lowered
- Cold air from the surroundings rush in to occupy the space vacated by warm air
- This promotes convection of air
Wind Speed and Air Pressure
- Increased wind speed is accompanied by reduced air pressure
Generation of wind currents on earth
Uneven heating between the equator and the poles
- As the warm air rises near the equator, and the cooler air from the regions in the 0–30 degrees latitude belt on either side of the equator moves in
- These winds blow from the north and the south towards the equator
- At the poles, the air is colder than that at latitudes about 60 degrees.
- The warm air at these latitudes rises up and the cold wind from the Polar Regions rushes in, to take its place
- In this way, wind circulation is set up from the poles to the warmer latitudes
- In reality, the winds don’t flow in the north-south or south-north direction as we expect. It changes in direction as shown below
- This change in direction is caused by the rotation of the earth
Uneven heating of land and water
- Land gets heated faster and also radiates heat faster than oceans
- The air over the land gets heated and rises.
- This causes the winds to flow from the oceans towards the land.
- These are monsoon winds
- In winter, the direction of the wind flow gets reversed
- It flows from the land to the ocean
- Thunderstorms develop in hot, humid tropical areas
- The rising temperatures produce strong upward rising winds.
- These winds carry water droplets upwards, where they freeze, and fall down again.
- The swift movement of the falling water droplets along with the rising air create lightning and sound.
- It is this event that we call a thunderstorm
Thunderstorm à cyclone
- Before cloud formation, water takes up heat from the atmosphere to change into vapour.
- High up in the air, water vapour then changes back to liquid (as raindrops),
- When it does that, the heat is released to the atmosphere.
- The heat so released, warms the air around.
- The air tends to rise and causes a drop in pressure.
- More air rushes to the centre of the storm.
- This cycle is repeated.
- This leads to the formation of a very low-pressure system with very high-speed winds revolving around it, called cyclone. (figure below)
Factors contributing to the formation of cyclones
- Wind speed
- Wind direction
Destruction Caused by Cyclones
- The low pressure in the eye lifts water surface in the centre.
- The rising water may be as high as 3–12 metres
- As a result, the seawater enters the low-lying coastal areas
- Apart from causing loss of life and property, it also reduces the fertility of the soil
- High-speed winds accompanying a cyclone can damage telephones and other communication systems, uproot trees and impairs the infrastructure of the region
- The entire east coast of India is vulnerable to cyclones than the west coast
Different names of cyclones
- It is called a ‘hurricane’ in the American continent.
- In Philippines and Japan it is called a ‘typhoon’
- A dark funnel shaped cloud that reaches from the sky to the ground
- Most of the tornadoes are weak but strong ones might travel at a speed of 300 kmph
- Tornadoes may form within cyclones.
- In India, tornado is not very frequent
By the government
- A Cyclone alert or Cyclone watch is issued 48 hours in advance of any expected storm
- A Cyclone warning is issued 24 hrs in advance
- Rapid communication of warnings and safety precautions to the Government agencies, the ports, fishermen, ships and to the general public
- Construction of cyclone shelters in the cyclone prone areas,
- Administrative arrangements for moving people fast to safer places
By the people
- Make necessary arrangements to shift the essential household goods, domestic animals and vehicles, etc. to safer places
- Keep ready the phone numbers of all emergency services
- Should not ignore the warnings issued by the meteorological department
- Avoid driving on roads through standing water
- Always store drinking water for emergencies
- Do not touch wet switches and fallen power lines
- Cooperate with the rescue and relief efforts and help others