Atmospheric Pressure and Winds — Question 11
Back to all questions(i) Doldrums extend from 0 to 5° North and South of Equator. Due to the vertical rays of the sun here, there is intense heating. The air expands and rises as convection current, causing a low pressure to develop here. Hence, Doldrums is a low pressure belt.
(ii) Equatorial regions have low atmospheric pressure throughout the year because atmospheric pressure decreases with increase in temperature. This is because when the temperature rises, air expands. The molecules of air move far apart and hence exert less pressure. On the contrary, with decrease in temperature, the air gets compressed and the space between molecules decreases and exerts more pressure on the region.
(iii) In the sub-tropical region the descending air gets divided into two parts. One part blows towards the Equatorial Low Pressure Belt. The other part blows towards the Circum-Polar Low Pressure Belt. This zone is marked by ascent of warm Sub-Tropical air over cold polar air blowing from poles. Due to earth's rotation, the winds surrounding the Polar region blow towards the Equator. Centrifugal forces operating in this region create the low pressure belt, known as Circum-polar low pressure belt.