(A) Explain the causes of tropical revolving storms. (8)
One of the causes of tropical revolving storms is the rotation of the Earth. For a cyclone to form a certain amount of ‘spin’ is needed to initiate the characteristic rotating motion of a tropical cyclone. The influence of the Earth’s rotation on the surface is known as the Coriolis Effect. This increases with distance away from the Equator and also explains why hurricanes do not usually form in region 5oN – 5oS. Another cause of tropical revolving storms is atmospheric instability. An atmosphere which cools fast enough with height and is unstable enough that it encourages thunderstorm activity can result in the formation of tropical storm. This is because the thunderstorm activity allows the heat stored in the ocean waters to be liberated for the tropical cyclone development. Little change in the wind with height is another cause of tropical revolving storms. Winds from different directions at altitude prevent a tropical cyclone from gaining height and intensity. Large values of wind shear tend to disrupt the organisation of the thunderstorms that are important to the inner part of a cyclone. Tropical revolving storms are also caused by a sea surface temperature in excess of 26oC. This explains why they are formed in low latitudes during the summer, when temperatures are at their highest. Warm waters are necessary to fuel the heat engine of the tropical cyclone. Relatively moist layers near the mid-troposphere (5 km) can also one of the causes of tropical revolving storms.
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