(a) Sea surface temperatures are low
(b) Inter-Tropical Convergence Zone seldom occurs
(c) Coriolis force is too weak
(d) Absence of land in those regions
Answer: (b)
Tropical cyclones are violent storms that originate over oceans in tropical areas and move over to the coastal areas bringing about large scale destruction caused by violent winds, very heavy rainfall, and storm surges. This is one of the most devastating natural calamities. They are known as Cyclones in the Indian Ocean, Hurricanes in the Atlantic, Typhoons in the Western Pacific and South China Sea, and Willy-willies in Western Australia. Tropical cyclones originate and intensify over warm tropical oceans. The conditions favourable for the formation and intensification of tropical storms are
O Large sea surface with a temperature higher than 27° C.
O Presence of the Coriolis force.
O Small variations in the vertical wind speed.
O A pre-existing weak low-pressure area or low-level-cyclonic circulation. y Upper divergence above the sea level system.
Option (b) is correct: In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclones do not originate due to the Inter-tropical Convergence Zone, which seldom occurs.
O The Intertropical Convergence Zone (ITZC), which shifts toward the north in our summer and toward the south in the southern summer, usually stays at or north of the equator in the Atlantic Ocean.
O A broad convergence zone like this need to reach about 5 degrees of latitude away from the equator in order for the Coriolis Force to have sufficient intensity to organise a full fledged tropical cyclone, and the Atlantic ITCZ almost never shift that far south, while the Monsoon trough in the Indian and Australian basins, and the western South Pacific, regularly do so. The eastern South Pacific is just about as void of activity as the South Atlantic, due largely to the ITCZ also having a tendency to stay near or north of the equator and to climatologically cool sea surface temperatures.
