Winds, Storms and Cyclones class 7 Notes

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Air is a mixture of gases. The gases present in air are as follows
  • Nitrogen 78%
  • Oxygen 21%
  • Carbon dioxide 3%and
  • Other gases like methane 0.03%
  • Water vapor

Properties of air

  • Air exerts pressure
  • Air moves from high pressure to low pressure
  • Pressure difference is created in the nature by the heat of the sun. When it falls on the earth surface, the surface of the earth gets heated and air above it also gets warm and becomes light weight and moves upwards.
  • Air expands on heating and contracts on cooling.
Why smoke always rises up?
As smoke contains hot air and hot air being lighter always rises up.


Winds, Storms and Cyclones Class 7 Notes
  • Moving air in the atmosphere is called wind. When air blows in slow speed it is pleasant but when it blows at a high speed it can be destructive. The wind is caused by differences in atmospheric pressure which is mainly caused by temperature difference. Uses of wind include- Windmills (to generate electricity)
  • Wind is defined by two parameters- direction and speed.
  • The speed of wind can be measured by the instrument called Anemometer.
  • Whereas the instrument used to measure wind direction is called wind vane.

What causes winds? Or Wind current

  • Winds blow due to difference in pressure between different areas. This can be explained as follows-
  • Unequal heating between the equator and the poles causes the cold air from the north and south poles to move towards the equator where the air is warm. As warm air near the equator moves up, cold air from the colder regions rush in to take up that space. This flow of air causes winds.
  • Uneven heating of the land and water surfaces causes two types of breezes as sea breeze and land breeze. Land breezes come from land while sea breezes come from the ocean or other water bodies.

Difference between land and sea breeze

Land breeze
At night, the land cools down faster than water in sea. So, the air above the sea is warmer than the air over the land surface. As it is lighter, the warmer air over the sea rises up, creating a low-pressure area above the water surface. So, the cool air from the land rushes to take its place and this phenomenon is referred to as land breeze.
Sea breeze
During the day the land absorbs heat better than water. This makes the air close to the land surface warmer. The warmer air rises up, creating a low-pressure area on the land surface. The cool air from the sea rushes to take its place and this phenomenon is referred to as sea breeze.

Monsoon winds

The winds blowing from the sea towards the land are loaded with moisture and bring rain. These winds that bring rain are called monsoon winds.
An Indian Ocean is mainly responsible to bring rain bearing monsoon winds to Kerala coast in June every year.


Winds, Storms and Cyclones Class 7 Notes
  • An atmospheric disturbance with very high-speed winds.
  • A natural phenomenon develops when the air has a lot of moisture that could result in the formation of clouds that could bring rain. This happens when the air is warm.
  • Thunderstorm accompanied by lightning can cause loss of life and material.
  • Thunderstorm occur in hot and humid tropical regions.
Precaution one should take in thunderstorm
  • Do not take shelter in metal shades as well as under trees.
  • Do not lie on the ground.
  • Do not sit near a window.
  • Do not use an umbrella with a metal end.
  • Do not stay in water.
  • If one is outside then it is advisable to take a shelter in a car.


Winds, Storms and Cyclones Class 7 Notes
A cyclone is referred to as a hurricane in America and as a typhoon in Japan and the Philippines. Cyclones can be defined as a natural phenomenon in which high speed wind causes due to differences in air pressure under certain conditions. As cyclone forms, the pressure in the center of the storm drops and this is referred to as eye of the storm. The center of the cyclone or eye storm is a clean area where there are no clouds but only light winds.
The formation of a cyclone depends upon different factors such as
  • Temperature of the place.
  • The wind speeds.
  • the direction of the wind
  • the humidity of the place.
Cyclone can result in extremely high waves in the sea or ocean because of the low pressure. The speed of the wind inside it is about 150-250km/hr. The speed of the wind decreases as it moves away from the eye of the storm.
Lot of destruction is caused by a cyclone
Fertility of the soil loses after a cyclone.
High speed wind in the cyclone uproots trees, damage houses and abuse loss of life and property.
Advanced technology helps in tracking cyclones and an efficient communication system can help in reducing the loss of life and property.
With the help of weather satellites, the weather conditions of a place can be continuously monitored. As it alerts the people in advance. If cyclone develops a cyclone alert is issued 48 hours in advance of the expected storm.
Safety measures on the part of the government in case of thunderstorm and cyclones
  • Forecast of a cyclone and warning of cyclone. Developing awareness among the people
  • Construction of cyclone shelters in cyclone prone areas.
Precaution by the people
  • Do not drink contaminated water.
  •  Do not touch a wet electrical appliance, switch as it causes damage to life.

Difference between a cyclone and a storm

The main difference between storm and cyclone is the speed of the wind and its direction.


Tornadoes is a very high funnel-shaped rapidly rotating column of air. The diameter of a tornado can range from one meter to several kilometers.
How tornadoes are formed?
Tornadoes are formed in thunderstorms when unstable hot air on the ground rises and mix with cooler air above. It can cause damage to life and property. The wind speed in tornadoes in extreme cases and reach up to 500 km/hr. The tornadoes can be formed within cyclone as well.

Water spouts

Tornadoes which are formed over the sea or water bodies are called water spouts.
Precautions to be taken during tornadoes
  • Avoid windows.
  • If driving park your car and go out from your car
  • Go to the basement or an inside room without windows on the lowest floor.
  • Keep radio or TV tuned to a local station for updates.
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