What is a cyclone?

A cyclone is a spinning storm that rotates around a low pressure centre. It has different name in different regions. If its formation takes place in the Atlantic Ocean or Northeast Pacific ocean, it is called a Hurricane whereas cyclones arising from the Northwest Pacific are called Typhoons and ones originating from the South Pacific Ocean and Indian Ocean are called Tropical cyclones.

Types of Cyclones:

Cyclones or rotating storms are largely categorised into three kinds- Tropical Cyclones, Polar Cyclones and Meso Cyclones.

Tropical Cyclones:

These kinds of cyclones are the most common ones and are formed in tropical ocean regions. Tropical cyclones mostly form in the mid summer or dry season. Cyclones can also be classified according to the speed of winds. Scientists have segregated these into five categories. Category one cyclones are the weakest, with winds rotating at a speed of 74-95 mph. Category five cyclones are the strongest and are described as the “Finger of god”. Winds rotate with a speed of over 155 mph in the category five cyclones.

Polar cyclones:

As the name suggests, these cyclones occur in the polar regions of Greenland, Siberia and Antarctica. Unlike tropical cyclones, polar cyclones are usually stronger during the winter. As they mostly occur in cold regions with scarce population, not much damage is done to life or property.

Mesocyclones:

Mesocyclone can be defined as a thunderstorm that spins into a gigantic tornado. All tornadoes are formed from thunder storms but not all thunderstorms whip up tornadoes.

Cyclone Formation:

Study of the formation of cyclones is called cyclogenesis. Scientists study the formation of cyclones ranging from micro scale to synoptic scale. A cyclone is formed from the upward movement of warm, moist air over the ocean near the surface. As the warm air rises, it produces an area of low air pressure below.

Air from surrounding areas with higher pressure pushes in on the low pressure area. The resulting cool air becomes warm and moist and hence beings to rise. The above cycle continues till a cyclone forms. As the warm, moist air rises and cools the water in the air forms clouds. The clouds, fed by the ocean’s heat and water, begin to rise.

As the storm system begins to gain momentum, its eye forms at the centre. The internal area of the eye has low pressure and hence is calm and clear while the outer layer of air with high pressure flow into the eye. When the winds of the rotating storm reach 39 mph (63 kmph), they form what is called a “tropical storm”.

If the wind speeds reach 74 mph (119 kmph), the storm now officially becomes a “tropical cyclone” or a hurricane. Tropical cyclones usually weaken when they hit the land because they are no longer fed by the energy from warm ocean waters. However, they often move far inland, dumping many centimeters of rain and causing excessive wind damage before they die out completely.

Extra-tropical cyclones are cold core cyclones and are formed due to change in the weather fronts. These later turn into cold core cyclones. A weather front is a boundary separating two masses of air of different densities. The main cause of this phenomenon is the change in temperature. Tropical cyclones are formed due to the latent heat driven by significant thunderstorm activity. They have a warm core.

Unlike the above two mesocyclones are warm core cyclones that are formed over land and further transform into tornados. Another source of the mesocyclone is the water sprout, which is an intense column and is mostly formed over a water body. They are connected to a towering cloud. They more often develop in environments of high instability and low vertical wind shear.