Winds, Storms and Cyclones - Class 7 Notes & Olympiad Questions

Winds

a) Wind is the movement of air in the Earth's atmosphere. The movement of air happens because of differences in temperature and pressure in different parts of the Earth.
b) Some areas of the Earth get more sunlight and become warmer, while other areas receive less sunlight and stay cooler. It creates variations in temperature and pressure. These differences cause air to move from areas of high pressure to areas of low pressure. This movement of air is what we call wind.
c) Wind can be gentle, like a light breeze that you feel on a pleasant day. It can also be strong and powerful, like during a storm, with heavy rain and strong winds. The intensity of wind depends on the differences in temperature and pressure in different areas.
d) When the air gets heated, it becomes lighter and expands, leading to lower air pressure. On the other hand, when the air cools down, it becomes denser, resulting in higher air pressure. This temperature difference causes warm air to rise because it is lighter, while cooler air comes in to replace it.
e) The speed of the wind is determined by the difference in pressure between two regions. The greater the difference in pressure, the faster the wind blows. So, if there is a significant difference in temperature between two places, you are likely to experience stronger winds.

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

Influence of Sunlight near the Equator
The regions near the equator receive the most sunlight because the Sun shines directly overhead. This sunlight heats up the air in these areas, causing it to rise. As a result, a low-pressure area is created. The cooler air from the surrounding regions near the equator moves towards this low-pressure area.

Effects of Temperature Variations at the Poles
Similarly, at the poles, the air is very cold and sinks close to the surface, creating a high-pressure area. The air in the surrounding regions is comparatively warmer and lighter. This warm air rises, creating a low-pressure area. The cold air from the surrounding polar regions rushes in to take its place.

So, to put it simply, the uneven heating between the equator and the poles creates differences in air pressure. Warm air near the equator rises, creating a low-pressure area, while cold air at the poles sinks, creating a high-pressure area. The movement of air from high-pressure areas to low-pressure areas creates wind currents.

Wind Currents Due to Uneven Heating of Land and Water

a) When it comes to heating up and cooling down, land and water behave differently. Land heats up and cools down much faster than water. This difference affects how winds move.
b) During the day, when it's hot, the land gets heated up more quickly than the nearby seas. As a result, winds blow from the cooler seas towards the hotter land. This phenomenon is called “sea breeze.” It is more prevalent in the spring and summer seasons.
c) These winds also bring moisture with them and can cause a weather pattern called monsoons. Monsoons are characterised by heavy rainfall and occur in many parts of the world.
d) At night the situation changes. The land, which cooled down faster than the water, becomes colder than the surrounding oceans. As a result, the wind direction reverses, and it starts to blow from the land towards the oceans. This is known as the “land breeze” and is more prevalent in the winter season.
e) This change in wind direction happens because land and water heat up and cool down at different rates. It's this uneven heating between land and water that causes the winds to move in specific ways during different seasons.

Measurement of Wind Speed

a) To accurately measure wind speed, scientists use a special instrument called an anemometer.
b) An anemometer is often installed on the top of buildings or other elevated structures.
c) By accurately measuring wind speed, scientists and meteorologists can better understand weather patterns and predict the formation of storms.

Thunderstorm

a) A thunderstorm occurs when the air moves violently with high speed. It is a weather event characterised by the swift movement of falling water, along with rising warm air, resulting in distinctive features such as sound (thunder), lightning, heavy rain, and strong wind.
b) Thunderstorms are typically found in hot and humid tropical areas.

Formation of Thunderstorms

a) Thunderstorms are formed when certain conditions come together in the atmosphere. There are three main ingredients needed for a thunderstorm to develop: moisture, unstable air, and something to make the air rise.
b) Thunderstorms usually occur in warm and humid places, where the air is hot and there is a lot of moisture. When the air gets heated up, it starts to rise because it becomes lighter. As it rises, it cools down, and the moisture in the air starts to come together to form clouds.
c) Inside these clouds, there are tiny particles of ice and water that bump into each other and create an electrical charge. This electrical charge builds up in the cloud until it becomes really strong. When it becomes too strong, it releases a big spark of electricity, which we see as lightning.
d) The lightning is like a big burst of energy that travels very quickly through the air. It heats up the air around it and creates a sound wave, which we hear as thunder. That's why we usually see the lightning first and then hear the thunder a little later.
e) During a thunderstorm, there can also be heavy rain and strong winds. Sometimes, the raindrops in the clouds freeze into ice and become hail, which can be quite large and fall from the sky.

Precautions During a Thunderstorm

It is important to take certain precautions to ensure safety during a thunderstorm:

1. Seek shelter indoors: Find a safe place inside a sturdy building, like your house or a school building. Stay away from windows and doors, as they can be dangerous during a storm.

2. Avoid open areas: Stay away from open fields, large bodies of water, and open spaces like parks during a thunderstorm. It's safer to be in an enclosed space.

3. Stay away from tall objects: Don't stand near or take shelter under tall trees, telephone poles, or anything that sticks out, as they can attract lightning.

4. Stay off electrical devices: Avoid using electronic devices like phones, computers, and gaming consoles during a thunderstorm. Lightning can travel through electrical lines and can cause damage.

5. Avoid water: Don't swim, bathe, or play in water during a thunderstorm. Water is a good conductor of electricity, and being in or near it increases the risk of being struck by lightning.

6. If you're outside and can't find shelter: If you're caught outside during a thunderstorm and can't find a building to go into, find a low-lying area away from tall objects. Crouch down with your feet together and your head lowered. Avoid lying flat on the ground.

7. Wait until the storm passes: Thunderstorms usually last for a short period of time. Wait until you no longer hear thunder or see lightning before going back outside or resuming outdoor activities.

Cyclone

a) A cyclone is a type of weather condition that involves a system of fast-moving winds swirling around a central area of very low pressure. It is a massive and intense storm that typically forms in warm and moist environments, often over the ocean in tropical regions near the equator.
b) It's a violent storm with extremely strong winds that can reach speeds of 150-250 kilometres per hour. These powerful winds are accompanied by heavy rainfall.
c) Cyclones are dangerous because of their immense size and the destructive force of their winds. They can cause significant damage to buildings, uproot trees, and create dangerous waves in the ocean. The heavy rains that accompany cyclones can also lead to flooding.
d) Cyclones mainly occur in areas where the ocean is warm and there is a lot of moisture in the air. The warm ocean provides the energy needed for the storm to develop, and the moisture in the air helps to fuel the formation of clouds and rainfall.

Formation of Cyclones

Cyclones are huge and powerful storms that form in warm and moist conditions, particularly over the ocean in tropical areas near the equator. Here's how they are formed:

a) Heating of the Air: When the air above the ocean's surface gets heated by the sun, it becomes warm and moist. This warm air rises because it is lighter than the surrounding air. As it rises, the water vapour in the air condenses and forms raindrops. This process releases heat into the atmosphere.

b) Spiral Motion: As the warm air rises, cool air from the surrounding areas rushes in towards the centre of the low-pressure region. However, due to the spinning of the Earth, the air doesn't move directly into the centre but starts to circle around it in a spiral. This spiralling motion forces more warm air to rise, creating a continuous cycle.

c) Low-Pressure Center: The repeated movement of warm air rising and cool air replacing it sets up a cycle of air currents. This results in a central area of very low pressure, with high-speed winds revolving around it. This weather condition is called a cyclone.

d) Eye of the Storm: In the centre of the cyclone, there is a calm and clear region called the "eye of the storm." This area is free of clouds and has light winds. The diameter of the eye can range from 10 to 30 kilometres.

e) Cloud and Rain Region: Surrounding the eye of the storm is a larger region, about 150 kilometres in size, filled with thick clouds and heavy rainfall. In this region, high-speed winds of 150-250 kilometres per hour are present. As we move away from this region, the wind speed gradually decreases.

Cyclones can cause significant destruction, as they have the power to destroy everything in their path.

Tornadoes

a) A tornado is like a fierce, spinning funnel of wind. The tornado takes the shape of a rotating funnel that can draw in debris, dust, and anything else near the ground, and then throw them out at the top.
b) The centre of a tornado has low pressure, meaning the air pressure is lower compared to the air around it. It can be around 10-20 per cent lower than the surrounding air pressure.
c) It's like a fierce wind tunnel that picks up things from the ground and flings them up into the air. The spinning motion of the tornado is what gives it its unique funnel shape.
d) Tornadoes can be very destructive because they have very strong winds that can cause damage to buildings, trees, and other structures. They can also throw objects around, which can be dangerous to people and property.

Precautions during Cyclones and Tornadoes

Some precautions to be taken during cyclones and tornadoes are:

1. Seek shelter in a safe place: When a cyclone or tornado is approaching, find a sturdy building and go inside. Seek shelter in a basement or an interior room on the lowest floor, away from windows and doors.

2. Listen to weather updates: Stay informed about weather conditions by listening to weather reports on the radio or television. Follow the instructions given by local authorities and evacuate if necessary.

3. Have an emergency kit: Prepare an emergency kit with essential items such as water, non-perishable food, a flashlight, batteries, a first aid kit, and a portable radio. Keep this kit easily accessible so you can grab it quickly if needed.

4. Stay away from windows: During a cyclone or tornado, stay away from windows and glass doors. Find shelter in a small, windowless room, if possible, to protect yourself from flying debris.

5. Crouch low and cover your head: If you cannot find shelter in a building, crouch down low to the ground with your head covered. Protecting your head with your arms can help reduce the risk of injury from flying objects.

6. Stay informed and calm: Keep yourself updated with the latest information about the storm and follow the guidance of trusted adults or local authorities. Remaining calm and following safety instructions can help you stay safe during these severe weather events.