The Tropical Monsoon Aims: to investigate the causes and characteristics of the tropical monsoon

Reading: Page 239 of Integrated approach

Explain the causes of the Summer Monsoon During the summer months the land is heated intensely and, because solids have a greater capacity for heat transfer. In June the ITCZ moves pole wards and extends to 30’N over northern India. An area of low pressure develops due to intense heating. Winds blow towards this low pressure from a south-westerly direction along the pressure gradient. The low pressure draws in moist air from the Indian Ocean.

Explain the causes of the Summer Monsoon As it rises over the land, due to the lands temperature increase caused by the migrating ITCZ, it becomes unstable from convection. Heavy rain results, with instability and further uplift being caused by the relief barrier of the Himalaya. Precipitation varies, Where the wind blows over the Bay of Bengal rainfall is extremely high. E.g. Cherrapunji:13 000 mm, compared to 2000 mm in Delhi. The average arrival date is 10th May in Kerala and 5th July on the Pakistan boarder.

Explain the causes of the Winter Monsoon In January the ITCZ moves over the equator and south towards the Tropic of Capricorn. An area of low pressure develops from intense heating. At the same time the continental landmass of central Asia experiences intense cooling due to the low specific heat capacity of the land. Winds move outwards from this high pressure towards the low. The air is dry due to its origins and the sinking warm air causes a decrease in humidity and a further drop in rainfall as it descends into the Indo-Gangetic plain. Bombay receives less than 100 mm during these 8 months. The winter monsoon usually retreats from northern India on 1st September and clears Kerala on the 15th November

Variations in the Tropical Monsoon

Climate Characteristics The biggest contrast is between the wet and dry seasons, but it is possible to distinguish between three seasons when taking into account temperature. March – May: Very hot and dry Temperatures rise to their highest levels before the ‘break’ of the monsoon rains. This is a result of …. June –September: hot and wet Over much if India 80% of the annual precipitation falls during these 4 months. Rarely is the rainfall continuous, but falls as a series of heavy pulses. October – February: warm and dry Once the wet monsoon ends, rains fall only occasionally. The general clear skis allow warm temperatures at night, but nights can be cooler in mid-winter months.