Winds Storms and Oceans

Start music   Jan 4 2017 || 11:14 PM


Air & Wind

  • Moving air is called wind
  • Warm air is lighter than cold air


Air Pressure

  • 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
  • Temperature
  • Humidity



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


Safety measures

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