Indian Geography Part 2: How the Monsoon Actually Works — Jet Streams, ITCZ and El Niño, Exam-Ready Notes

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Civil ExamsCivil Services1 min read

The monsoon is a system, not a date. Four drivers decide onset, strength and breaks.

On this page

  1. Drivers
  2. Mechanism and rhythm
  3. Variability
  4. Revise in 30 seconds

Drivers

  • Differential land-sea heating plus the northward shift of the ITCZ.
  • Tibetan Plateau summer heating acts as an elevated heat pump.
  • Subtropical westerly jet retreats north of the Himalaya before onset.

Mechanism and rhythm

  • Two branches: Arabian Sea (coastal Karnataka-Kerala-Gujarat) and Bay of Bengal (NE, then backed west up the plain).
  • MJO, a 30-60 day wave, sets active and break spells.
  • Retreat: October heat, lows over the Bay, NE monsoon rains on Tamil Nadu.

Variability

  • El Nino tilts weak; positive IOD rescues; La Nina tilts strong.
  • Normal onset over Kerala around 1 June; IMD forecasts with a plus-minus of 4 days.

Revise in 30 seconds

  • ITCZ + jet shift + Tibet heating = onset.
  • Two branches: Arabian Sea, Bay of Bengal.
  • El Nino bad, positive IOD good.
  • NE monsoon is the Tamil Nadu rainy season.

Quick revision

  • Differential land-sea heating plus the northward shift of the ITCZ.
  • Tibetan Plateau summer heating acts as an elevated heat pump.
  • Subtropical westerly jet retreats north of the Himalaya before onset.
  • Two branches: Arabian Sea (coastal Karnataka-Kerala-Gujarat) and Bay of Bengal (NE, then backed west up the plain).
  • MJO, a 30-60 day wave, sets active and break spells.
  • Retreat: October heat, lows over the Bay, NE monsoon rains on Tamil Nadu.