Monsoon rains may come two days earlier to the Andaman & Nicobar islands, but this will have no bearing on how soon it reaches Kerala.

• Monsoon typically sets in over Kerala by June 1, but there have been instances of powerful winds gusting into the Andamans and then stalling.
• Earlier this week, the agency had indicated that the threat to the Indian monsoon from an El Nino may have receded.
• Another sea anomaly, the Indian Ocean Dipole (that refers to oscillating temperatures in that ocean), was likely to be positive.
• A positive dipole buffered against an El Nino’s effects, but didn’t on its own improve chances of rains.

El Nino:

• El Niño events are associated with a warming of the central and eastern tropical Pacific, while La Niña events are the reverse, with a sustained cooling of these same areas.
• These changes in the Pacific Ocean and its overlying atmosphere occur in a cycle known as the El Niño-Southern Oscillation(ENSO).
• The atmosphere and ocean interact, reinforcing each other and creating a ‘feedback loop’which amplifies small changes in the state of the ocean into an ENSO event.
• Even in a neutral state, temperatures in the Pacific Ocean vary from east to west – for example, the western Pacific ‘warm pool’ in the tropical Pacific has some of the warmest large-scale ocean temperatures in the world.
• During an ENSO event, ocean temperatures become warmer than usual or cooler than usual at different locations, which are reflected in ocean temperature gradients.
• The most important driver of ENSO is these temperature gradients across the Pacific, both at the surface and below the surface, particularly at the thermocline.
• The term El Niño translates from Spanish as ‘the boy-child’. Peruvian fishermen originally used the term to describe the appearance, around Christmas, of a warm ocean current off the South American coast.
• La Niña translates as ‘girl-child’ and is the opposite ENSO phase to El Niño.

Indian Ocean Dipole (IOD)

• It is also known as the Indian Niño, is an irregular oscillation of sea-surface temperatures in which the western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean.
• The IOD involves an aperiodic oscillation of sea-surface temperatures, between “positive”, “neutral” and “negative” phases.
• Apositive phase sees greater-than-average sea-surface temperatures and greater precipitation in the western Indian Ocean region, with a corresponding cooling of waters in the eastern Indian Ocean-which tends to cause droughts in adjacent land areas of Indonesia and Australia.
• The negative phase of the IOD brings about the opposite conditions, with warmer water and greater precipitation in the eastern Indian Ocean, and cooler and drier conditions in the west.
• The IOD also affects the strength of monsoons over the Indian subcontinent.
• A significant positive IOD occurred in 1997-98, with another in 2006. The IOD is one aspect of the general cycle of global climate,interacting with similar phenomena like the El Niño-Southern Oscillation (ENSO) in the Pacific Ocean.

Source: The Hindu & Wiki