The purpose of the post is to explore the dynamics of monsoon trough development. With the differential heating of subcontinent winds from indian ocean flow towards subcontinent, the game start with the Bob winds which initially keep striking Ne states of India, Assam, Arunchal perdesh, Nmmt during April to mid May. Usually this time gradual heating of the subcontinent remains in progress. In late May to early june Cross equatorial winds start establishing, although the process is not continuous, its rather pulsating, but for the sake of understanding we will keep it simple and even would not discuss the multiple variables involve in the dynamics of Cef (cross equatorial flow).

During late may or june the south westerly component from Arabian sea(yellow) pushed by Cef from Gujrat coast enter in Ne states of India,(p1) where it interacts with the outflow of thunderstorms of Ne India and an east west convergence zone develops, under ideal conditions the process should expand to central India but due to heating of Tibetan plateau the outflow of subsequent thunderstorms flows, W, Nw(instead of Sw) direction along foothills of Himalaya towards upper Pakistan, where more hot /moist Sw winds interact with relatively cool/ moist outflow of let say foothills of Nepal thunder storm(p2) . The easterly outflow of thunderstorms (initially ignited by Eastern foothills of Himalaya)(blue line) vs Sw winds (yellow lines) creat a nw propagating convergence zone or trough (red line) usually between surface to 0.9 km Asl ( above mean sea level) along the foothills of Himalaya. If western Tibet and kashmir is Hot, the trough can extend upto foothills of Kashmir. Under adverse conditions ( frequent troughs in western Himalayan region) the process of east west trough may take several weeks from Ne India or Utter perdesh to Kashmir (p3) . Its called heat trough or east west trough until the full establishment of Sw Monsoon, there after its called monsoon trough or monsoon axis. Re establishment of monsoon trough dynamics are often more pronounced with an Ms break, which may occur around 10th July.

Next we will try do discuss north south movement of Western end of trough. Suggestions are also required for next topics from your side. Any questions or positive criticism is welcomed here

Yellow lines = Sw winds
P1’P2,P3 = ts phases
Blue line= thunderstorm outflows as e winds
Red line = Trough

Fahim Malik Dhurnal

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