Role of Tibetan Plateau in the Indian monsoon

Role of Tibetan Plateau in the Indian monsoon
Posted on 18-08-2023

The Tibetan Plateau serves as a pivotal heat engine in the intricate mechanism of weather patterns. Elevated between 4000 and 5000 meters, this expanse spans around 2.5 million square kilometers. It stands enveloped by snow-clad mountain ranges and boasts limited vegetation cover. Consequently, during summer, it becomes an epicenter of intense heating, emerging as 20 to 30 degrees Celsius warmer than the surrounding air.

As summer unfolds and the sun's apparent movement draws near the Tropic of Cancer, the Tibetan Plateau experiences prolonged periods of elevated temperatures. This phenomenon induces the ascent of air to the upper troposphere, giving rise to a high-pressure zone in this upper layer of the atmosphere. This process engenders anti-cyclonic conditions and establishes a notable difference in pressure between the land and ocean regions. The outcome of this pressure gradient is the movement of air masses towards the Indian subcontinent, propelled by the equatorial easterly jet stream. Upon reaching the vicinity of the Mascarene Islands, located near Madagascar, this air current commences its descent, ultimately arriving at the Indian subcontinent as the southwest monsoon.

Monsoons, the cyclic winds that alter their course with the shifting seasons, are influenced by various factors, with the Tibetan Plateau holding a pivotal role. The summertime heating of the Tibetan Plateau stands as a primary driver in initiating and sustaining the complex monsoonal circulation. The Tibetan Plateau's impact on the atmosphere is twofold:

(i) Serving as a Physical Barrier The expansive mountain range acts as a formidable barrier, obstructing the intrusion of cold, arid air from northern latitudes into the subcontinent. Simultaneously, it redirects and amplifies the warm, moisture-laden winds emanating from the oceans, which are instrumental in propelling the monsoon.

(ii) Functioning as a High-Level Heat Source The summertime elevation in temperature across the Tibetan Plateau transforms it into a source of elevated heat. This thermal engine engenders a high-level thermal anticyclone over the plateau's mid-tropospheric region during summer. From this anticyclone, winds emanate in a clockwise pattern across the plateau's expanse. These winds give rise to easterly jet streams situated above, flowing from East to West along the southern perimeter of this upper air anticyclone.

These upper-level easterly flows eventually descend upon the perennial high-pressure zone that forms over the southern Indian Ocean. This infusion intensifies the existing high-pressure conditions in the region. It is from this heightened pressure zone that the onshore winds originate, moving toward the thermally induced low-pressure sector evolving in the northern reaches of the Indian subcontinent. Upon traversing the equator, these surface winds undergo a directional shift, culminating in the formation of the South-West monsoon.

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