The Dynamic Notion: Shifting Dynamics of the Inter-Tropical Convergence Zone (ITCZ)

H. Flohn, an expert from the German Weather Bureau, introduced this theory in 1951. According to his viewpoint, the monsoon system in tropical Asia emerges as a result of seasonal shifts in the global wind pattern, known as the planetary wind system. These seasonal variations stem from the changing temperature and pressure belts in this region, influenced by the varying position of the sun overhead. The primary winds in the tropical zone are referred to as trade winds.

During both March and September, the sun is positioned directly over the equatorial region in the tropics. This intense solar heating generates a zone of low pressure. This low-pressure zone attracts the north-east trade winds from the northern hemisphere and the south-east trade winds from the southern hemisphere. The convergence of these trade winds results in ascending air and the formation of a low-pressure region known as the Inter-tropical Convergence Zone (ITCZ).

As the apparent position of the sun shifts towards the Tropic of Cancer, the location of the ITCZ changes accordingly. By July, the ITCZ resides at approximately 20°N-25°N latitudes, often termed the monsoon trough. This monsoon trough creates a low-pressure zone over northern and northwestern India. The shift of the ITCZ causes the south-east trade winds of the southern hemisphere to traverse the equator within the longitudes of 40° and 60°E. These trade winds alter their course due to the Coriolis force and shift from blowing southwest to northeast. This phenomenon is known as the 'southwest monsoon'.

In the winter months, as the sun's apparent movement shifts towards the Tropic of Capricorn, the ITCZ migrates southward, triggering a reversal in wind direction across the Indian subcontinent. Consequently, the wind starts to blow from the northeast to the southwest. This seasonal wind pattern is termed the 'northeast monsoon'.

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