Winds, Storms and Cyclones Class 7 Science Notes - Chapter 8
Winds, Storms and Cyclones Class 7 Science Notes - Chapter 8
Air Pressure
The continuous physical force exerted on an object or against an object when something comes in contact with it, is called pressure.
- Air exerts pressure in different ways under different situations and on all objects and in all directions.
- Air pressure helps the leaves of trees, banners or flags to flutter when the wind is blowing.
Wind Currents
The natural motion of air, due to a current in a particular direction is called as wind.
Winds and pressure difference
- Reduced air pressure is associated with increased wind speed
- Air flows from a high-pressure area to a low-pressure area.
Warm air and cool air
- High-speed winds are accompanied by reduced air pressure.
- 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
The wind is the movement of air which depends on the difference in air pressure in two regions.
- Air moves from the region of high pressure to the region of low pressure in the atmosphere.
- This difference in air pressure is created by uneven heating or unequal heating on the earth.
- Wind currents due to uneven heating of land and water
- Land absorbs and emits heat at a much faster rate than water. During the summer, winds blow from cooler seas to hotter land. These winds transport moisture, resulting in monsoons.
- During the winter, the wind flow is reversed and moves from land to the oceans
1. Uneven Heating between the Equator and the Poles
The region of the earth which is closed to the equator of the earth gets the maximum heat from the sun.
Therefore, the air in these regions gets warm and rises, creating an area of low air pressure.
The cooler air from the region of up to 30 degrees latitudes belt on either side of the equator moves or rushes towards the equator and replaces the warm rising air.
2. Uneven Heating of Land and Water
During summer, the earth near the equator warms faster than the water in the oceans.
Therefore, the winds flow from the oceans towards the land.
It is a part of the water cycle.
These rain-bearing winds are called the monsoon winds.(ii) During winter, the direction of the wind gets reversed.
The wind blows from the land to the sea due to the difference in air temperature between the land and sea.
Hence, bring only a small amount of rain in the winter season.
Thunderstorms
When the pressure of air drops, it indicates the possibility of a storm.
Thunderstorms are produced by the dark clouds which form at fairly low altitude in the atmosphere.
Therefore, it can be said that to occur a thunderstorm, it requires moisture, rapidly rising warm air and sea breeze or mountains.
Precautions to be Taken During a Thunderstorm
A thunderstorm is accompanied by lightning which is a giant electric spark.
Therefore, you must take the following precautions during a thunderstorm to protect ourselves from the lightning.
When you are in open area
Do not take shelter under an isolated tree or building. If you are in a forest, take shelter under a small tree. Do not lie on the ground.
Do not take shelter under an umbrella having a metallic end.
Never sit near a window, open garages, storage sheds, metal sheds, etc, to take shelter.
One can take shelter in a car or a bus.
Do not go in the water. If you are in the water, get out and go inside a building.
When you are inside
Do not sit near an open window. Close the doors and windows properly.
Do not touch/operate any electrical devices or telephone.
Do not watch TV
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 as the eye of the storm.
Structure of a Cyclone
The eye of a cyclone is a calm area in the center of the storm. It has a diameter of about 10 to 30 kilometers.
A 150-kilometer-wide cloud region surrounds the eye. Winds can reach speeds of up to 150-250 km/h.
As the wind moves away from the eye, its speed gradually decreases.
Types of Cyclones
Different parts of the world have different names for cyclones. In the United States, they are referred to as hurricanes, while in Japan, they are referred to as typhoons.
Tornado
Within a cyclone, a tornado can form. It is shaped like a rotating funnel that collects debris, dust, and other particles at the bottom and expels them at the top.
It has a diameter ranging from a metre to a kilometer and can reach speeds of up to 300 km/hr.
Safety Measures and Role of Advanced Technology
Steps to follow if a storm is followed by lightning
Don't hide out under solitary trees.
If you're in a forest, find a small tree to hide under.
Never lay on the ground.
Avoid attempting to hide under an umbrella.
Do not sit close to metal sheds or uncovered garages.
If in water, immediately exit and enter a building.
A safe place to hide is inside of a car or a bus.
Measures of safety from tornados
forecasting and warning system for cyclones.
rapid warning systems for authorities, fishermen, and residents of danger zones.
building of hurricane shelters and quick evacuation plans.
Stay away from downed power lines.
collaboration with rescue teams and other parties.
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