Winds, Storms and Cyclones Class 7 Science Notes - Chapter 8

According to the CBSE Syllabus 2023-24, this chapter has been removed from NCERT Class 7 Science textbook.

Air Pressure

Air pressure

• The air around us exerts pressure. This is seen in the following activity:
• A tin can is filled with water heated over a flame. As soon as the water comes to a boil, the lid is put on, and it is kept under running cold water. We find that the shape of the can get distorted.
• Inference: When cold water is poured over the can, some of the steam in the can condenses, reducing the amount of air inside the can. The air from outside compresses the can from outside, thereby distorting it. This shows that air exerts pressure.

Wind Currents

Wind

The natural motion of air due to a current in a particular direction is called as wind.

Winds and Pressure Difference

• Increased wind speed is accompanied by reduced air pressure.
• Air moves from a region of high pressure to a region of low pressure.

To know more about “Movement of Air”, visit here.

Warm Air and Cool Air

• On heating, air expands and rises up. Since it expands, it takes up more space and therefore becomes lighter.
• Warm air is lighter than the cool air. That is why smoke always rises up.
• Once warm air rises up, air pressure is lowered. Then the cold air from the surroundings rushes in to fill its place.

Wind Currents

A wind current is a current of air, sometimes of considerable force, moving generally horizontally from areas of high pressure to areas of low pressure.

Wind currents due to uneven heating of land and water

• Land gains and loses heat much faster than water. During summer, winds move from cooler seas towards the land, which is hotter. These winds carry moisture and cause monsoons.
• During winter, this direction of wind flow is reversed, and it moves from land towards the oceans.

Rain

Rains are caused when winds from the oceans and seas flow towards land carrying moisture. The moisture in the clouds gets saturated after a point and pours down as showers, which we call monsoons.

To know more about Rain, visit here.

Storms and Cyclones

Wind Currents Due to Uneven Heating between the Equator and the Poles

• The regions in proximity to the equator receive the highest amount of heat from the sun, and the warm air rises up. The air from latitudes 0-30⁰ moves in from north and south to take its place.
• Similarly, the air at the poles is much cooler than the air around latitudes of 60^0, which is comparatively warmer. This warmer air rises up while the cool air from the poles races inside to occupy its place. Subsequently, wind currents move from poles to warmer latitudes due to uneven heating of the earth’s surface.

To know about Different Types of Storms, watch the below video

Thunderstorms

Thunderstorms develop in areas that are very hot and humid, like India. The high temperatures create strong upward currents that carry water vapour to high altitudes, where they condense and fall down again. Due to such drastic pressure variations, they are accompanied by lightning and strong winds.

Thunderstorm to Cyclone Conversion

• During a thunderstorm, water releases heat when it changes from vapour to rain in the atmosphere. This warms the air around and creates a drop in pressure.
• This causes air to rush in towards the centre of the storm. This cycle causes large low-pressure systems accompanied by strong high-speed winds that swirl around it. This is the formation of a cyclone.

Cyclone

• A cyclone is a large mass of air that rotates violently about 1015 km high in the air.
• The centre of the cyclone is a calm area called the eye of the storm.

Structure of a Cyclone

• The centre of a cyclone is a calm area called the eye. It has a diameter of about 10 – 30 km.
• Around the eye is a region of clouds of about 150 km. This also has winds with speeds of up to 150-250 km/hr.
• The speed of the wind gradually decreases as it moves away from the eye.

For more information on the Structure of a Cyclone, watch the below video

Types of Cyclones

Cyclones are given different names in different parts of the world. They are called hurricanes in the American continent and typhoons in Japan.

Tornado

• A tornado occurs within a cyclone. It is in the shape of a rotating funnel that sucks in debris, dust and everything at the bottom and throws them out at the top.
• Its diameter ranges from a metre to a kilometre with speeds of up to 300 km/hr.

Coriolis Effect

The force due to the Earth’s rotation that tries to deflect winds towards left or right is known as the Coriolis effect.

To know more about Thunderstorms and Cyclones, visit here.

Safety Measures and Role of Advanced Technology

Steps to follow if a storm is followed by lightning

• Avoid taking refuge under isolated trees.
• If in a forest, seek shelter under a small tree
• Do not lie on the ground
• Do not try taking cover under an umbrella
• Avoid sitting near metal sheds or open garages
• If in water, rush out and go inside a building
• A car or a bus is a safe place to take cover.

To know more about Safety Measures during Thunderstorms and Lightning, visit here.

Measures of Safety from Tornados

• Cyclone forecast and warning system.
• Rapid warning systems to Governments and fishermen, and people in prone zones.
• Construction of cyclone shelters and rapid evacuation schemes.
• Avoiding fallen power lines.
• Cooperation with others and rescue teams.

To know more about Safety Measures and the Role of Technology, visit here.