The Inter Tropical Convergence Zone (ITCZ) or Thermal Equator is a broad trough of low pressure in equatorial latitudes (it always remains on the north of the equator due to effect of landmass). This is where the northeast and the southeast trade winds converge and this is a low pressure zone. This convergence zone lies more or less parallel to the equator but moves north or south with the apparent movement of the sun. At the time of monsoons, it shifts towards north (towards India) and hence attracts moisture laden winds.
According to meteorologists, Monsoon is the result of the shift of the ITCZ under the influence of the vertical sun towards Tropic of Cancer. The ITCZ being the zone of lowest pressure in the tropical region, is the target destination for the Trade winds of both the hemispheres. Consequentially, with ITCZ at the Tropic of cancer (over Indian peninsula), the South East Trade winds of the Southern Hemisphere have to cross the equator to reach the ITCZ. However, due to Coriolis Effect, these South East trade winds are deflected eastwards in the Northern Hemisphere transforming into South West trades. These pick up the moisture while traveling from sea to land and cause orographic rain once they hit the highlands of the Indian Peninsula. This results in the South-West Monsoon.
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