Tropical cyclone UPSC - Cause,type and formation

Tropical Cyclone (Formation of tropical cyclone)

we know that Cyclone Nisarga and Amphan have come to India this year in coastal areas of Gujarat and Odisha respectively. Amphan cyclone was a super cyclonic storm with speed up to 200kmh while Nisarga having speed ranging from 100-120kmh. So in this post, we will learn about what is a Tropical cyclone for UPSC, how is it formed, and its causes and effects.


In this post we are going to learn about tropical cyclones for UPSC, NDA and SSC. The first thing you need to understand is that tropical cyclones originate over oceans in tropical areas and coastal regions. The tropical region is the region of the earth near to the equator and between the Tropic of Cancer in the northern hemisphere and the Tropic of Capricorn in the southern hemisphere.

Tropical region

Name of tropical cyclone

Tropical cyclones are known by different names depending on the region.

1.  In the Indian Ocean, they are known by simply cyclones
2.  The western Pacific side or near The South China Sea it is called as typhoons
3.  Near Western Australia, it is known by  willy willies.
4.  Similarly, near southern America, they are known as hurricanes. All these are different names refer to the same type of storm.

picture of cyclone

As we know that tropical region receives the most solar radiation per area and the reason behind that is due to the incoming solar radiation that is direct and vertical at the tropical region and as you move towards the polar region the angle of the sun rays are not vertical, they are slanting rays

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Vertical rays of sunlight are more effective in producing light and heat than slanting rays and that's why the tropical region is warm.

Pressure belts of earth

Now let's understand about wind movement when the movement is determined by low pressure and high-pressure systems it is the differences in atmospheric pressure that creates pressure gradient and makes the wind move and the wind always blows from the areas of high pressure to low-pressure areas.

Pressure belts of earth

Cause of low pressure and High-pressure belts

Now the next question is what causes low pressure and high pressure. Low pressure occurs when air is warm either from being over a warm land or ocean surface that means low pressure occurs at a place which is warm and how does a place become warm because of the incoming heat from the Sun.   
That is why a tropical region is a perfect place where low pressure occurs similarly high pressure occurs when air is cool either from being over a cool land or ocean surface.

Coriolis force

The polar region is a high-pressure zone and always remembers rain blow from the high pressure to low-pressure areas while all of this happens there's another important phenomenon which come into the picture is Coriolis force due to the rotation of the earth.

Coriolis force

The earth rotates towards the east and that's why the Sun, Moon, planets, and stars all rise in the east and go towards the west.

Due to the rotation of the earth, there is a force that is generated and it acts perpendicular to the direction of motion and to the axis of rotation.

We also know that earth is a sphere and it is much wider in the middle as a result the speed of the surface of the earth at the equator is much faster than the speed at the poles. So if anything has to come straight from the poles towards the equator it gets deflected to the right in the northern hemisphere and to the left in the southern hemisphere and this force is called the Coriolis force.

It causes fluids like water and air to curve as they travel across or above the earth's surface due to Coriolis force. The air in the northern hemisphere gets deflected to the right side.

The air in the northern hemisphere curves to the right while moving from high pressure to the low-pressure area similarly, in the southern hemisphere, the air is deflected to the left side while moving from high pressure to the low-pressure area.

Now you have understood why the air moves to the left and right due to Coriolis force.

It is because of this reason there are certain pressure belts all over the Earth's surface you must be familiar with this picture which shows global wind circulation the pattern you can see that at different latitudes there are different pressure belts their existence is simply due to the movement of air to the left and right due to Coriolis force.

Now we have to understand how the air turns into a storm and what causes the spinning of a cyclone. When we look at the movement of a cyclone, the center of every cyclone or hurricane will have an area of low pressure which attracts the cool air because air moves from high pressure area to low-pressure area.

Eye of cyclone

It means the outer area of a cyclone consists of cool air coming from the high-pressure area which surrounds the central low-pressure area. This region is called the eye of the storm or center of this storm.

cyclone image

The low-pressure region is warm the region where the air is warm which expands and then Rises the cool air from high-pressure zone rushes in to fill the void left by the rising warm air. This air warms and becomes moist as well allowing it to rise then more cool air rushes in to fill the void.

The warm moist air cools as it rises higher into the atmosphere because the temperature drops with increasing altitude that is also how clouds are formed.

Now this process continues again and again as a result you will see an eye like figure at the center of the storm.

Now comes the Coriolis effect in the northern hemisphere, the cool air rushing towards the center of the storm is deflected slightly to the right but keep in mind the cool air keeps getting attracted to the center.

The warm low-pressure zone is while moving towards the center, the cool air keeps getting deflected, now this creates spin in a counterclockwise direction in the southern hemisphere. The Coriolis effect moves air to the left opposite to what happens in the northern hemisphere, as a result, the spinning of this cyclone is in a clockwise direction in the southern hemisphere.

cyclone image

Tropical cyclones are intense and in the beginning we have read that it occurs over the ocean surface and coastal region because there is a continuous supply of moisture from the ocean or sea.

When it reaches the land the moisture supply is cut off and the storm dissipates when the cyclone crosses the coast because after that the landmass starts.

So the place where tropical cyclone crosses the coast is called the landfall of the cyclone.

The power of this cyclone naturally decreases because the supply of moisture is cut off.

The average diameter of a circulating tropical cyclone can vary between 150 and 250 kilometers, however the diameter of this storm over the Bay of Bengal Arabian Sea
and the Indian Ocean is between 600 to 1200 kilometers. These cyclones move slowly at a speed of about 300 to 500 kilometers per day.

if we look at the height of the cyclone, the circulation of the tropical cyclone extends up to the troposphere and it is around 15,000 to 18,000 meters.

Cyclone image

When warm moist air rises up in the atmosphere after a certain height, it starts cooling because the temperature drops with increasing altitude. As the air cools, it becomes denser and moves towards the ground this is called subsiding warm air. This intensifies this storm by increasing the diameter of this storm.

As the diameter increases these spiral rain bands expand and push the rain clouds into the outer region.

Tropical cyclones occur at the time of maximum solar radiation during the summer and autumn season that is around July to October time in the Northern Hemisphere and December to March time in the southern hemisphere.

so we have studied the formation of the tropical cyclones, the eye of a cyclone, the landfall of a cyclone, causes of tropical cyclones, types of a cyclone, and Coriolis effect which is asked in a various exam like UPSC IFS and other forest service examination.