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During the Indian monsoon season
Explanation
During the Indian summer monsoon season (June to September), the upper-level atmospheric circulation undergoes a significant shift. The subtropical westerly jet stream, which prevails over the north Indian plains during winter, withdraws and shifts north of the Himalayas [c1][c2]. Following this withdrawal, the Tropical Easterly Jet (TEJ) sets in, typically along 15°N latitude [c1][t2]. This easterly jet is a unique feature of the northern hemispheric summer over southern Asia and is considered responsible for the 'burst' of the monsoon [c1][c5]. While the westerly jet exists north of the Tibetan Plateau, it is absent from the Indian region (the area south of the Himalayas) during the peak monsoon months [c1][t7]. Therefore, within the Indian region specifically, only the easterly jet stream exists during the monsoon season [c1][t9].
Sources
- [1] INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.) > Chapter 4: Climate > Onset of the Monsoon > p. 31
- [2] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 4: Climate of India > JET STREAM AND INDIAN MONSOON > p. 8
- [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 27: Jet streams > The Tropical Easterly (TEJ) Jet or African Easterly Jet > p. 389
- [4] https://en.wikipedia.org/wiki/Tropical_Easterly_Jet