Monsoon

1996
May-October is the wet season. Briefly explain what causes the wet season. (4 marks)

Between May and October the sun moves overhead between the equator and the Tropic of Cancer. The high angle of the sun in the sky causes the land mass of Asia to heat up and temperatures to rise. This warm air rises due to convection and creates a low pressure area over Northern India. Air always moves from high pressure to low pressure areas and so consequently winds blow onshore from the high pressure area centred over Australia. These S/ SW winds are funnelled up the Bay of Bengal and so pick up water vapour and this creates the wet summer monsoon season.

2003 Q3aiii Explain how the tropical monsoon is caused (6 marks)

The sun is overhead at the Tropic of Cancer in June and this causes high temperatures. The intense heat of the sun causes warm air to rise and low pressure to develop. As winds blow from high pressure to low pressure air is drawn into Bangladesh from the high pressure system to the south causing south-westerly winds to blow in from the Bay of Bengal. These onshore winds pick up moisture and consequently bring the summer monsoon rains.
In winter the sun is overhead at the Tropic of Capricorn. This means that it is at a lower angle in the sky and the land is cooler over the continent of Asia. Cold sinking air forms a high pressure system over Bangladesh and now winds blow off shore towards the high pressure system to the south over the Indian Ocean. These north-easterly winds are cold and dry.