Major features of Indian monsoon

Indian monsoon is a seasonal wind system that reverses direction between summer & winter. Fig: seasonal reversal of winds showing ITCZ, Bay of Bengal, Arabian sea, Indian subcontinent monsoon patterns. 1. Seasonal reversal of winds - winds blow from sea to land in summer & land to sea in winter. 2. Two branches - Bay of Bengal & Arabian sea. 3. Uneven distribution - both spatial & temporal (Mawsynram vls Jaisalmer). 4. Retreating monsoon - begins in monsoon September & causes NE monsoon in Tamil Nadu. 5. Monsoon breaks - decline in rainfall.

1. Differential heating of land & sea leads to low pressure zone on land & high pressure over oceans. This gradient drives moist winds to Indian subcontinent. 2. Tibetan plateau heating - strengthens monsoon trough. 3. El Nino - leads to rainfall deficit (eg. 2015) & La Nina causes stronger monsoon winds & above normal rainfall (eg. 2012). 4. Indian Ocean Dipole - positive IOD (warmer western Indian Ocean) strengthens monsoon. 5. Madden Julian Oscillation (MJO) - if it present over Indian Ocean intensifies low pressure system & increases rainfall. 6. Jet streams - subtropical westerly jetstream & tropical easterly jetstream (summer) influence monsoon. 7. Bay of Bengal & Arabia sea - sea surface evaporation & fluxes fuel monsoon. 8. Arctic amplification - warming Arctic impairs monsoon bogth, may delay onset of rainfall. 9. Orography & topography - Himalayas block cold air, Ghats cause orographic uplift - higher rainfall on windward sides.