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Monsoon onset over Kerala delayed

Topics Covered: Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclones etc.

Monsoon onset over Kerala delayed:


Context:

The India Meteorological Department (IMD) has said that the arrival of the southwest monsoon over Kerala has been delayed to June 3.

However, Skymet, a private weather forecast agency, said the monsoon had arrived. This was because two of the three criteria — as defined by the IMD — had been met.

The criteria are:

  1. Rain-bearing westerlies being at a minimum depth and speed.
  2. At least 60% of the available 14 stations in Kerala and coastal Karnataka reported rainfall of 2.5 mm or more for two consecutive days after May 10.
  3. A certain degree of clouding, indicated by a parameter called ‘outgoing longwave radiation’ (OLR), being below 200 W/square metre.

Currently, IMD’s own data indicated that except for the OLR, the other criteria were met. Thus, there is an element of subjectivity in arrival.

Factors influencing the onset on Southwest Monsoon:

The onset of Southwest Monsoon is an emotional event as it may cause anxiety if delayed or shoot excitement for stepping in early.

Various factors influencing it’s onset:

The onset needs a trigger in the form of a weather system in the proximity of the coastline. These are ocean born phenomena which accentuate the monsoon surge around the normal time of onset. These include:

  1. The low-pressure area or depression in the Bay of Bengal during the last days of May or the beginning of June.
  2. There are such systems in the Arabian Sea as well around the same time which results in onset over the mainland.
  3. Cyclonic Vortexis another factor which appears in the Southeast Arabian Sea, off Kerala and Lakshadweep region. They also shift along the west coast to push the monsoon current.
  4. The formation of ‘trough’ off the west coast due to temperature differential between land and sea. This situation could be for a mild start and weak progress.
  5. Lastly the cross-equatorial flow, wherein the trade winds from the Southern Hemisphere crossover to the Northern Hemisphere can bring a strong monsoon surge towards the Indian mainland.

Monsoon in India- related key facts:

  1. Generally, across the world, the monsoons are experienced in the tropical area roughly between 20° N and 20° S.
  2. Out of a total of 4 seasonal divisions of India, monsoon occupies 2 divisions, namely- the southwest monsoon season and the retreating monsoon season.

 

Insta Curious:

  • Do you know that the Indian summer monsoon rainfall is influenced by a system of oscillating sea surface temperatures known as the Indian Ocean Dipole (IOD)? Read here
  • If you are more curious and would like to know how India Ocean Dipole also affects floods & bushfires in Africa and Australia respectively, Read here

 

InstaLinks:

Prelims Link:

  1. What is El Nino?
  2. What is La Nina?
  3. What is ENSO?
  4. When do these events occur?
  5. Impact of ENSO on Asia, Africa and Australia.
  6. What is Indian Ocean Dipole?
  7. Differences between Southwest and Northeast monsoon.
  8. Factors influencing the onset of Southwest Monsoon.

Mains Link:

Discuss the impact of La Nina weather phenomenon on India.

Sources: the Hindu.