Southwest monsoon delay

Southwest monsoon delay

Subject: Geography

Context:

The southwest monsoon, one of the most stable weather systems on the planet, has gone for a toss in 2021. As on July 12, the country-wide deficit of monsoon rainfall stands at seven per cent below normal.

Concept:

Reasons for Delay

• the progress and rains happened because coincided with cyclones, Tauktae in the Arabian Sea and Yaas in the Bay of Bengal, just before the onset of monsoon rains, ‘onset’  of monsoon because the cyclone dragged the monsoon trough onto Kerala and it met the definition of the onset
• The monsoon is delayed due to lower-than-usual temperatures in northern Pakistan and northern India because it takes a longer time to heat these regions to monsoon temperature.
• It led to the absence of the formation of the low-pressure system over the north Bay of Bengal. However, nature abhors a vacuum. As a result, suitable conditions occur for the appearance of synoptic-scale
• Rossby waves in between the African Jet and mid-latitude westerly winds that led to the longest break and heatwaves in Delhi, are unlikely to have affected the Indian monsoon .
• Madden Julian oscillation and Indian Ocean Dipole. The Madden Julian Oscillation is an eastward moving pulse of cloud and rainfall

Rossby Waves

• The meandering jet streams are called Rossby Waves.
• Rossby waves are natural phenomenon in the atmosphere and oceans due to rotation of earth.
• In planetary atmospheres, they are due to the variation in the Coriolis effect (When temperature contrast is low, speed of jet stream is low, and Coriolis force is weak leading to meandering) with latitude.
• Rossby waves are formed when polar air moves toward the Equator while tropical air is moving poleward.
• The existence of these waves explains the low-pressure cells (cyclones) and high-pressure cells (anticyclones).

Madden Julian Oscillation

• It is an eastward moving cyclic weather along the tropics. It influences rainfall, sea surface temperature, winds.
• It consists of two phases. Enhanced Rainfall Phase and Suppressed Rainfall Phase.
• Rainfall Phase: winds at the surface of the earth converge to push the air upwards throughout the atmosphere. This rising air increases condensation and rainfall.
• Suppressed Rainfall Phase: The winds at the top of the atmosphere converge and forces the air to sink down. As air sinks, it dries and suppresses rainfall.
• The El Nino, Indian Ocean Dipole and Madden Julian Oscillation are the atmospheric and oceanic phenomena that affect the weather on a large scale.
• The Indian Ocean Dipole pertains only to the Indian Ocean. However, the other two affects weather till mid latitudes.
• When the Madden Julian Oscillation is over the Indian Ocean, it brings good rainfall for the Indian subcontinent. On the other hand, when it stays longer over the Pacific, it dries up Indian Monsoon winds.