Many People would be surprised if we were to say Sun is the foremost reason for the Monsoon Dynamics Across Earth. Facts are sometimes stranger than Fiction. Indeed the Monsoon Dynamics are primarily driven by the energy provided by the Sun Light.
In simple terms Monsoon dynamics are a large scale replica of how Sea Breeze Pattern happens over coastal areas. Due to day time heating the air particles rise up leaving behind a vacuum providing an opportunity for the denser air from the Sea to move in along the gradient leading to what we call the evening Sea Breeze.
Monsoon Dynamics work on similar principle, just that due to the tilting angle of Earth we have different periods of Summer between the Northern & Southern Hemisphere. When the Northern Hemisphere has its summer the air over the Indian Sub Continent is evacuated leading to a Thermal Low Pressure bringing in the Monsoon Winds & Rains along with it. This creates an area of convergence, Intertropical Convergence Zone (ITCZ), an area of convection that drives the Monsoon dynamics.
The transit of ITCZ between the Northern Hemisphere to the Southern Hemisphere following the Sun provides us for Northeast Monsoon. This is the reason why sometimes in academic circles the Northeast Monsoon is called the Retreating Monsoon.
This video thanks to Yale University & UCAR illustrates the whole monsoon dynamics and the movement of the ITCZ between the two hemispheres along with the Hadley Circulation, a loop of Rising & Sinking Air dynamics that is part of the overall mechanism of Monsoon. The position of this Hadley Circulation is also an important part of the monsoon equation leading to Suppressed / Enhanced Monsoon Dynamics.
As one can observe in the chart the current Location of ITCZ is south of Equator firmly establishing itself in the Southern Hemisphere. The Australian Cyclone Season has kickstarted been by Cyclone Yvette set to hit the NW coast shortly. Similarly models are indicating for some tropical cyclone activity to evolve after Christmas in South Indian Ocean around the Mauritius region. All this are indications of the monsoon dynamics shifting to the Southern Hemisphere which saw its summer solstice on December 21st the day that indicates the start of the summer season.
While we have the Trough of Low present in Andaman Sea that is expected to move W/NW towards the Indian Mainland with the dynamics now more skewed towards Southern Hemisphere northward propagation of Monsoon dynamics in the North Indian Ocean will be limited keeping the disturbances and associated convection activity towards the lower latitudes along the Equator. Models though indicate a fair bit of rainfall activity to happen over Coastal Tamil Nadu particularly in the areas to the South of Delta and associated region of Sri Lanka. As days pass by we will see the Northeast Monsoon wind by from our shores.
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