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CYCLONE SITRANG - IAS Academy in Coimbatore

CYCLONE SITRANG

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Bangladesh has been devastated by Cyclone Sitrang, which slammed into densely-populated, low-lying areas.

• A tropical cyclone is an intense circular storm that originates over warm tropical oceans and is characterized by low atmospheric pressure, high winds, and heavy rain.
• A characteristic feature of tropical cyclones is the eye, a central region of clear skies, warm temperatures, and low atmospheric pressure.
• Storms of this type are called hurricanes in the North Atlantic and eastern Pacific and typhoons in SouthEast Asia and China. They are called tropical cyclones in the southwest Pacific and Indian Ocean region and Willy-willies in north-western Australia.
• Storms rotate counterclockwise in the northern hemisphere and clockwise in the southern hemisphere.

The conditions favourable for the formation and intensification of tropical storms are:

• Large sea surface with temperature higher than 27°C.
• Presence of the Coriolis force.
• Small variations in the vertical wind speed.
• A pre-existing weak low- pressure area or low-level-cyclonic circulation.
• Upper divergence above the sea level system.

Tropical Cyclones Formation

Formation and Initial Development Stage:

• The formation and initial development of a cyclonic storm depends upon the transfer of water vapour and heat from the warm ocean to the overlying air, primarily by evaporation from the sea surface.
• It encourages formation of massive vertical cumulus clouds due to convection with condensation of rising air above the ocean surface.

Mature Stage:

• When a tropical storm intensifies, the air rises in vigorous thunderstorms and tends to spread out horizontally at the tropopause level. Once air spreads out, a positive pressure at high levels is produced, which accelerates the downward motion of air due to convection.
• With the inducement of subsidence, air warms up by compression and a warm ‘Eye’ (Low pressure centre) is generated. 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, internal warmth and extremely high speeds, as soon as its source of warm moist air begins to ebb or is abruptly cut off.