Describe any three factors which affect the mechanism of monsoon
The phenomenon of monsoon refers to the seasonal reversal of winds. The offshore winds that blow from north-east direction are reversed into onshore south western winds. This phenomenon is based upon differential heating of land and ocean bodies. During summer in the Indian subcontinent, the large landmass gets heated up more rapidly than the neighbouring seas. As a result, the air above land expands and rises up. The moisture laden winds arrive on the western coast of India from the south western side and cause heavy rainfall on the windward side of the Western Ghats. The leeward side, however, receives little rain. Further rain occurs in the northern plains and north-east parts of India with the branching of the monsoon. The monsoon is also aided by the Inter Tropical Convergence Zone or monsoon trough near the equator where winds from northern and southern hemisphere merge. The landmass of the Indian subcontinent cools up around September with the sun retreating south. The ocean bodies, which lose heat slowly, retain the summer heat. The cooler high pressure air moves towards the low pressure over the ocean and causes the retreating north-east monsoon. It mainly causes rainfall along the eastern coast of India.
India being a tropical country, major part of the Indian subcontinent experiences tropical climate throughout the year. However unlike other tropical countries India has an unique climate. Main three factors that make the Indian mainland gain this uniqueness are - Mighty Himalayas, typical Indian Monsoon and of course the two seas - Arabian sea and Bay of Bengal. Lets see how these three factors affect Indian climate majorly in detail. Himalayas- Being one of the youngest and tallest mountain range in the world, Himalayas act as the prime factor in influencing the Indian climate. Himalayas mainly prevents the cold continental air from Central Asia entering Indian Subcontinent, keeping the Indian subcontinent warmer than the same longitudinal temperate regions in other parts of the world. Apart from this, Himalayas blocks the Indian monsoon current from Arabian sea and Bay of Bengal and diverts it across the Northern Indian plains. If Himalayas were absent, Indian subcontinent would be a desert with absence of rain and harsher winters! Indian Monsoon - India has two typical monsoons - 1. South West Monsoon and North East Monsoon. South West Monsoon (SWM) contributes to 80% rainfall of major landmass of Indian subcontinent. During Indian summer, landmass over Thar desert heats up abnormally forming a heat low pressure area around May end. This low pressure pulls in the monsoon current over Indian mainland. SWM has two branches which gains its name from the sea they emerge namely Arabian sea and Bay of Bengal. Arabian sea current emerges from a vast high pressure area which forms over South Indian ocean around May and gets deflected over the east coast of Africa towards Indian mainland. Bay of Bengal current emerges from the South Andaman sea and flows in a south east direction towards the Indian mainland. Himalayas blocks both the rushing Indian monsoon current and deflects it to flow into the low pressure area and thus covering the entire landmass of Indian subcontinent. North East Monsoon(NEM) or Retreating SWM - Unlike SWM, NEM do not have a defined source. However some factors can be identified as factors influencing NEM. As Sun starts moving south after Autumn equinox (Sep 22), northern landmass of Indian subcontinent starts to cool off rapidly resulting in a high pressure area. This pushes cold winds from Himalayas into Indian landmass making colder climates. However when this cold air passes through Bay of Bengal picks up significant moisture and precipitates NEM over Tamilnadu, Andhra Pradesh and Kerala during Oct-Nov-Dec. Apart from this, low pressure areas from South China sea emerges into Bay of Bengal and brings in Tropical cyclones which majorly affects the east coast of India during NEM. Apart from the two major Indian monsoons, a third weather front brings significant precipitation to Indian mainland ie Western Disturbance. Western Disturbance are nothing but low pressure systems which form over Mediterranean sea and travels east across the globe. When this systems encounter the Western Himalayas, they precipitate rain and snow over northwestern plains of Indian subcontinent during winters. Indian seas - Both Arabian sea and Bay of Bengal are capable of hosting cyclones throughout the year. Apart from the cyclones, both seas are accountable for the daily weather of the longer Indian coast of around 7516km. During summer, sea breeze from both seas cools down the coastal cities like Chennai, Mumbai and Kolkata faster than the inner regions. However they are also responsible for keeping these cities warm and humid even during the winters.