Answer the following questions in about 150 words.
(i) Discuss the factors affecting the speed and direction of wind.
(ii) Draw a simplified diagram to show the general circulation of the atmosphere over the globe. What are the possible reasons for the formation of subtropical high pressure over 30o N and S latitudes?
(iii) Why does tropical cyclone originate over the seas? In which part of the tropical cyclone do torrential rains and high velocity winds blow and why?
(i) The speed and direction of the winds is influenced primarily by 3 factors:
• Pressure Gradient Force: the Pressure gradient forces are stronger in areas where the difference in pressure from one isobar to another is higher, this exerts and inward force along high pressure areas and outward force along low pressure areas. It influences the
• Frictional Forces: The frictional forces affect the velocity of wind. These forces are strongest along the surface and decrease with increasing elevation, as the air at the surface is denser and more prone to viscous effects. About 3km above sea level, the effect of friction is negligible.
• Coriolis Force: The rotation of the earth around its axis exerts a force on the winds. It acts perpendicular to the isobars, and deflects the wind towards right in northern Hemisphere, and towards left in Southern Hemisphere.
(ii)
The possible reasons for the formation of high pressure belts over 30 degree latitudes on both sides are:
• The convective currents along the equator, caused by high insolation, give rise to a low pressure area along the ITCZ. The air from this region rises upwards, and moves towards the poles. Hence, there is an accumulation of air along the 30 degree latitudes. This air sinks down and creates STH. This sinking is caused by the cooling of air.
(iii) Tropical Cyclones originate over the tropical seas and oceans because they meet all the conditions necessary for their development:
• Large surface areas and temperatures over 27 degrees
• Influence of Coriolis Force
• Minimal variations in vertical wind speed.
• Presence of weak low pressure area.
• Upper divergence above sea level system.
Also, the supply of moisture from the sea strengthens the storm continuously.
Torrential rains and high velocity winds are found along the “EYE-WALL” of the storm. This is so because the central area or the eye is the area of subsiding warm air, and the winds circulate around this area, causing torrential rain. There are outward emanating clouds and rain bands, which extend up to 600-1200 km from the eye.