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Vinson Kurian

Thiruvananthapuram, Jan. 11 Leading climate models have seemingly reached a consensus that late-in-the-season La Nina conditions have developed over the equatorial Pacific.

The La Nina is likely to continue into the northern hemisphere spring 2009, according to the National Oceanic and Atmospheric Administration of the US.

The Tokyo-based Frontier Research Centre for Global Change (FRCGC) has gone a step further and forecast that this ‘cooling event’ (compared to the warming El Nino) over the Pacific might extend into early 2010.

The La Nina may have been in the making as early as October 2008, say some researchers. This might have had a say on winter climes which have been late to arrive over northwest India and lacking in marked rainfall events in what resembles a play-out of conditions during the comparable period last year.

Analysing the conditions then, Prof Toshio Yamagata, Programme Director at the FRCGC, had said that anomalous atmospheric convection in La Nina winters caused high pressure to develop over the Mediterranean region - the source region for western disturbances (WDs) which determine the strength of the northwest Indian winter.

This caused the upper tropospheric westerly jets, carriers for WDs, to become weak and lie north of their normal positions. The number of WDs that managed to reach the Indian region got curtained in this manner.

The polar, northerly component of WDs (as against warm, moist southwesterlies) got magnified in the bargain, setting colder than normal winter over northwest India. A waxing and waning cold wave has accounted for more than 70 deaths until now in northwest India, but without any major rainfall event.

Meanwhile, the western Himalayas are bracing to receive a fresh western disturbance mid-week to end of this week. Scattered snowfall/rainfall has been forecast over Jammu and Kashmir, Himachal Pradesh and Uttarakhand.

Fog-to-shallow fog conditions prevailed over parts of east Uttar Pradesh, Bihar, Madhya Pradesh and southeast Rajasthan until Sunday morning. These are likely to continue during the next 1-2 days as well. Cyclonic circulations have been traced to over Jammu and Kashmir, Punjab and north Maharashtra and adjoining south Gujarat.

Despite the unusually late start to the La Nina, expected impacts during January-March 2009 include above-average precipitation over Indonesia and below-average precipitation over the central and eastern equatorial Pacific.

As for India, there is near-model consensus of slightly above normal rainfall for the southern parts during December-January-February 2009. La Nina is conventionally known to impact the monsoons over the sub-continent but without direct cause-effect relationship.

The FRCGC too has predicted above normal rain for the southern Indian peninsula during this quarter. Periodical accentuation of the zone of tropical convergence and passing easterly waves might help sustain wet conditions over Sri Lanka and south peninsular India.

The US-based Centre for Ocean-Land-Atmosphere Studies expects isolated wet weather events to hold over coastal Tamil Nadu and later extreme south peninsula until January last.

The northeast monsoon has officially drawn to a close but easterly wave action has not stopped over the Bay of Bengal. In fact, a weak wave has been causing isolated showers over parts of the region over the past few days.

More Stories on : Climate & Weather | Climate & Weather

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