Agri Business

La Niña well-established, may last into early March next: Australian Met

Vinson Kurian | | | Updated on: Dec 08, 2021
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Not sure yet if La Niña will stay longer in time for Indian monsoon

The Australian Bureau of Meteorology has said that La Nina has been firmly established in the tropical Pacific and cited climate models as suggesting it will persist likely into early March-April-May in 2022, just ahead of the start of India’s summer monsoon (South-West monsoon).

La Niña in the Pacific refers to a seasonal phenomenon in which the western basin (closer to India) warms relative to the eastern basin, where sea-surface temperatures (SSTs) dip. It has vibed well with a concurrent Indian monsoon in the past, though there is no direct cause-effect relationship.

‘Double dipping’ event?

The US Climate Prediction Centre has not taken a call on whether the current La Niña will last into the next Northern Hemisphere summer. Last year (2020-21) has been a La Niña year; if it were to sustain into 2021-22 (second consecutive year), it would constitute another ‘double dipping’ event.

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‘Double dipping’ is used in the context of SSTs dipping in the East Equatorial Pacific (even as they rise in the West as mentioned earlier) for a second year to mark La Niña. The US Climate Prediction Centre is of the view that it is too early to suggest that La Niña will recur into 2022 summer and beyond.

Makes or mars monsoon

As mentioned earlier, 2020-21 has been a La Niña year already. It was preceded by alter-ego El Niño before tapering to a neutral phase (neither La Niña or El Niño). El Niño is the exact reverse of La Niña in which the West Pacific cools with disastrous consequences for India, though with exceptions.

SSTs can make or mar a monsoon season depending on which side of the Pacific warms up relative to the other. Warm seas beyond a threshold 27.5-degrees Celsius facilitate evaporation, cloud-building, formation of low-pressure areas/depressions/cyclones and therefore heavy rain and floods.

‘Double dips’ in the past

If one goes back further to recent history, one can find that year 2016-17 was a variously El Niño-neutral-La Nina year followed by a neutral-to-La Niña in 2017-2018. Both these years are considered essentially La Niña years because of the comparably longer period during when it held sway.

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Other consecutive La Niña years listed by the US Climate Prediction Centre are 2010-11/2011-12; 2007-08/2008-09; 1999-2000/2000-01; 1983-84/1984-85 and 1970-71/1971-72. So ‘double dipping’ (La Niña) events have been quite common, though the same cannot be said of EL Nino.

La Niña thresholds

The Australian Bureau said that SSTs in the Equatorial Pacific have cooled to La Niña thresholds, with model outlooks expecting them to cool further. In the atmosphere, cloud and wind patterns are typical of La Niña, indicating the atmosphere is responding to the changes in ocean temperatures.

This feedback process is known as ‘coupling’, and it means La Niña conditions are now expected to be locked in until at least the end of December-January-February. Nearer home, the negative Indian Ocean Dipole (IOD) is near its end, with IOD index values in the neutral range.

Negative IOD phase ends

The IOD is the El Niño/La Nina-equivalent that rolls out periodically in the Indian Ocean. During a negative IOD phase, the East Indian Ocean basin warms up relative to the West and vice versa. The IOD too has a major say in how monsoons in India can pan out during a given year.

However, the Australian Bureau said some signs of the negative IOD persist with increased cloud over the East Indian Ocean and strengthened westerly winds. Climate models predict the IOD will remain neutral for the coming months, consistent with its typical seasonal cycle.

Published on December 08, 2021

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