Five Weather Systems Impacting Indian Monsoon

Syllabus: GS1/Climatology

Context

• India’s southwest monsoon may remain weak or stalled for a week, with five rain-suppressing factors active at the same time.

About

• India recorded a 38% countrywide rainfall deficit between June 1 and June 17, with central India facing the highest deficit at 62%.
• Five rain-suppressing factors are: Developing El Niño conditions, weak Madden-Julian Oscillation activity, dry westerly winds, a weak Somali Jet and neutral Indian Ocean Dipole conditions.

Southwest Monsoon

• Onset and Retreat: The monsoon season in India generally starts in early June and lasts until September.
  • The onset of the monsoon is marked by the arrival of the southwest monsoon winds, which bring moisture-laden air from the Indian Ocean.
  • The withdrawal or retreat of the monsoon typically begins in October.
  • The northeast monsoon, occurring from October to December, brings rainfall to parts of southern India.

Factors Impacting Monsoon

El Nino

• El Niño means Little Boy in Spanish. It is a climate phenomenon characterized by the periodic warming of sea surface temperatures in the central and eastern equatorial Pacific Ocean.
  • During El Niño, trade winds weaken. 
  • Warm water is pushed back east, toward the west coast of the Americas and as a result cold water is pushed towards Asia.

• Impact of El Nino on weather patterns: It leads to rise in global temperature, weakens monsoon, increases risk of wildfires and triggers extreme weather events such as hurricanes, and cyclones, particularly in the Pacific Ocean and Atlantic.

Madden-Julian Oscillation (MJO)

• The MJO is a moving system of winds, clouds, and pressure that brings rain as it circles around the equator. It was discovered in 1971 by Roland Madden and Paul Julian.
• The system travels eastward at 4–8 m/s and circles the globe typically every 30–60 days, though it can take up to 90 days.
• As it moves, strong MJO activity often splits the planet into two parts — one in which the MJO is in active phase and brings rainfall, and the other in which it suppresses rainfall.
  • During an active MJO phase, regions within its influence experience above-average rainfall, often due to increased cloud formation, convection, and cyclonic activity.

Western Disturbance

• A Western Disturbance (WD) is an extra-tropical weather system that originates outside India and moves from west to east, bringing rain, snowfall, and storms to northern parts of the Indian subcontinent.
• Origin and Formation: Western disturbances originate over the Mediterranean region, Black Sea, or Caspian Sea.
  • They form when cold polar air interacts with warmer, moist air, creating low-pressure systems.
  • These systems are carried eastward by westerly winds in the upper atmosphere, particularly the subtropical westerly jet stream.

Indian Ocean Dipole:

• In 1999, N H Saji of Japan discovered an ENSO-like phenomenon in the Indian Ocean which they named the Indian Ocean Dipole (IOD).
  • Like ENSO, IOD also has three phases—positive, negative and neutral. During the positive phase of IOD, sea surface temperatures are warmer in the western Indian Ocean which gives a boost to monsoon winds.
  • The reverse happens during IOD negative and no gradient is observed during the IOD neutral period.

Somali Jet

• It is a fast moving inter hemispheric cross equatorial flow of air which originates near Mauritius and the northern part of Madagascar in the southern Hemisphere. 
  • The winds cross the Equator and move along the eastern coast of Africa through Kenya, Ethiopia, and Somalia.
  • During May, the jet moves into the Arabian Sea, and by June it reaches the west coast of India.
  • As it travels, it carries a large amount of moisture (water vapour) from the ocean.
  • When the Somali Jet becomes stronger, it brings heavier and more reliable monsoon rainfall to Peninsular India.

Source: DTE