Lesson: Winds, Storms and Cyclones
The centre of a cyclone is an area of calm and it is called the ______ of the storm.
When air opposes the motion of a moving object, it is called ____________.
Wind currents are generated due to unequal _______ of the earth.
What does the movement of air from high pressure region to low pressure region give rise to?
What is humidity?
Amount of water vapour in the atmosphere
Define air pressure.
The pressure which is exerted by air on all bodies at all times in all directions is called air pressure.
Why does the sailor find it difficult to sail his boat against the direction of wind?
The sailor finds it difficult to sail his boat against the direction of wind because air exerts pressure and tries to push it backwards.
What are cyclone alert and a cyclone warning?
A warning issued 48 hours before the expected time of a cyclone is the cyclone alert.
A warning issued 24 hours before the expected time of a cyclone is the cyclone warning.
Why do thin, light metal roof sheds get blown off on a stormy weather?
Increase in wind speed gives rise to an area of low pressure above the roof whereas the air pressure below the roof is high. This pushes the roof upwards and leads to the sucking up of the thin, light metal roof shed which gets blown away by the strong winds on a stormy weather.
What causes lightning and thunder during a thunderstorm?
The swift movement of the falling droplets of water from the sky along with the rising air causes lightning and thunder during a thunderstorm.
What all factors create a cyclone?
Wind direction, wind speed, humidity and temperature together create a cyclone.
Explain with illustration, the uneven heating on earth.
The equatorial belt is the hottest place on earth. The region on the either side of the equator receives maximum amount of heat from the sun. The area is thus the area or low-pressure belt. 30° latitude is a high-pressure belt in comparison to the equator and hence air flows from sub-tropical belt to equatorial belt or doldrums.
As Earth rotates from west to east, the direction of wind flowing from a low-pressure belt to a high-pressure belt is not straight but slanting. These winds are known as Trade Winds.
Air rising from the equator becomes cooler and descends at 30° latitude. This region thus remains a high-pressure belt. On the other hand, the region near 60° latitude is hotter than the pole and hence is a low-pressure belt. Air from the polar region as well as tropical region move towards 60° latitude giving rise to winds called Westerlies and Polar Easterlies.
Explain with an experiment to prove that air exerts pressure.
Put some water in a can and heat it till the water becomes steam. Hold the can with a tong and immediately invert and dunk this hot can in ice water.
You will observe that the shape of the can gets distorted. This happens because when you heated the can you caused the water in it to boil. The water vapour from the boiling water pushed air out of the can. This can, filled with water vapour, was suddenly cooled by inverting it in ice water tray. Cooling the can caused the water vapour in the can to condense, creating a partial vacuum. The extremely low pressure of the partial vacuum inside the can made it possible for the pressure of the surrounding outside air crush the can. This is because the pressure difference is greater than the can is able to withstand and it gets crushed. This shows that air exerts pressure.
Differentiate between sea breeze and land breeze.
During the daytime, the land warms up faster than the neighbouring water bodies, like sea and river. The air above the land on receiving heat becomes light and rises up. As a result, a low-pressure region is created. The water body, being comparatively cooler, the air above it too is cooler, and is therefore a region of high pressure. So, the wind blows from the sea to occupy that low pressure region above the land. Since the wind blows from sea to land, it is known as the sea breeze.
On the other hand, during the night time, the land cools faster than the water body. As a result, the air above the land becomes cooler than the air above the sea. So, the air above the sea being lighter rises up giving rise to an area of low pressure above the sea region. As a result, the cooler air from above the land region blows towards the sea, giving rise to the land breeze.
What is a cyclone? How does it develop?
A cyclone is a weather condition where a violently inward rotating mass of air, which is 10 to 15 km high, swirls violently around a strong centre of low atmospheric pressure.
Before cloud formation, water takes up heat from the atmosphere to change into vapour. When water vapour changes back to liquid form as raindrops, this heat is released to the atmosphere. The heat released to the atmosphere 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. The chain of events ends with the formation of a very low-pressure system with very high-speed winds revolving around it. During this swirling around the eye of the cyclone, which can have a diameter of upto 30 km, the ferocious wind rises as high as 10-15 km. The violent region of spin around the eye is around 150 km which can cause serious damage to lives and property that comes in its way.
Factors like wind speed, wind direction, temperature and humidity contribute to the development of cyclones.
What are the helpful safety measures that can be taken to combat the cyclones?
In order to combat the cyclones, the following safety measures should be taken:
· Setting up of a cyclone forecast and warning service
· Rapid communication of cyclone forecast and warning to the government agencies, the ports, fishermen, ships, airlines, and to the general public
· Building of cyclone resistant building that can withstand cyclones
· Construction of cyclone shelters in the cyclone prone areas
· Administrative arrangements for moving people fast to safer places
· Relocate people with the help of rescue squad when instructions for evacuation have been issued