Formation Cyclones

UPSC Exam Preparation: Topic of the Day – Formation of Cyclones

Cyclones are characterized by their destructive potential to damage structures such as houses, lifeline infrastructure such as power and communication towers, hospitals, food storage facilities, roads, bridges, culverts, crops, etc., due to high-velocity winds.

Exceptionally heavy rainfall causes flooding. Storm surge inundates low-lying areas in the coastal areas resulting in loss of life and destruction of property, besides eroding beaches and embankments, destroying vegetation and reducing soil fertility.

The development cycle of tropical cyclones may be divided into three stages:

Formation and Initial Development Stage

The initial development and formation of a cyclonic storm depend upon various conditions. They are:

• A warm sea (a temperature in excess of 26 degrees Celsius to a depth of 60 m) with abundant and turbulent transfer of water vapour to the overlying atmosphere by evaporation.
• Atmospheric instability encouraging formation of massive vertical cumulus clouds due to convection with condensation of rising air above ocean surface.

Mature Tropical Cyclones

When a tropical storm intensifies, the air rises in vigorous thunderstorms and tends to spread out horizontally at the tropopause level. A positive perturbation pressure at high levels is produced, once air spreads out which accelerates the downward motion of air due to convection. With the inducement of subsidence, air warms up by compression and a warm ‘Eye’ is generated.

The ‘Eye’ of the cyclonic storms has three basic shapes:

(i) Circular

(ii) Concentric

(iii)Elliptical

The main physical feature of a mature tropical cyclone in the Indian Ocean is a concentric pattern of highly turbulent giant cumulus thundercloud bands.

Modification and Decay

A tropical cyclone begins to weaken in terms of its central low pressure, extremely high speeds and internal warmth, as soon as its source of warm moist air begins to ebb, or is abruptly cut off. Modification and decay happens after its landfall or when it passes over cold waters. However, the weakening of a cyclone does not mean that the danger to life and property is over.

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