Describe and explain the atmospheric processes responsible for the tropical monsoon climate and assess the extent to which human activity is influenced by this climate.

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Katherine Smith

Describe and explain the atmospheric processes responsible for the tropical monsoon climate and assess the extent to which human activity is influenced by this climate.

Monsoons are cyclical wave-like air masses that occur in the sub-tropics, moving onto land from the sea during the summer and returning over water in winter. The word monsoon comes from the Arabic mausim, meaning “season,” because these storms return year after year.  The monsoon climate is found along the coastal regions of southwest , , , , Southwestern Africa, , northeast and southeastern . Monsoon zones exist all around the world, but they all have two seasons, wet and dry, caused by winds, which blow in opposite directions. In some monsoon regions, such as those in China and Japan there can be rainfall all year round, although most of it will still fall in the wet, summer season.

All monsoons share three basic physical mechanisms: differential heating between the land and oceans (adiabatic heating); Coriolis forces due to the rotation of the Earth; and the role of water which stores and releases energy as it changes from liquid to vapour and back (latent heat). The combined effect of these three mechanisms  produces the monsoon's characteristic reversals of high winds and precipitation.

One of the most important variable is the timing of the beginning of the wet season in the Tropical Monsoon Climate. This onset date propagates across the Indian subcontinent from the Bay of Bengal towards the interior bringing the intense rains. The reverse process, the monsoon retreat, marks the end of the wet season, and travels from the interior out towards the Bay of Bengal.

Monsoons are caused by land-sea temperature differences due to heating by the sun's radiation. The winter monsoon lasts for 8 months.  The continental landmass cools rapidly resulting in extremely low temperatures over central Asia. As temperature drops, atmospheric pressure rises and an intense high pressure system (anticyclone) develops over Siberia. Cold air flows out of Siberia as northwesterlies and turns into northeasterlies on reaching the coastal waters of China before heading towards Southeast Asia.  The air is dry because Central Asia is a semi-desert.   As the air moves Southwards towards India, it crosses the Himalayas.  This dry air rises over the mountains, producing a little rain orthographically on the Northern side.  As this even drier descends it warms up adiabatically because it is sinking and moving away from the mountains resulting in very dry conditions.

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The Summer Monsoon lasts for 4 months.  Intense solar heating leads to scorching temperatures over the Asian landmass.  As hot air expands and rises upwards, a semi-permanent low-pressure area develops. As this warm air rises, cooler air from the sea moves in to replace it bringing with it the very moist air that causes the exceptionally high rainfall (convectional and orthographic) associated with monsoons, along with the fact tat the ITCZ has moved north. Moist southeasterlies originating from the southern Indian Ocean and the Indonesian-Australian region transforms into southwesterlies on crossing the equator and flow across Southeast Asia before converging ...

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