The Hindu Business Line : Cold, dry winter a La Nina offshoot: Experts

Thiruvananthapuram, March 11 A fortuitous combination of a climatological event with a non-event triggered the cold spell in February over northwest India, apart from sending out some of the worst-ever snowstorms that chilled the Chinese northwest.

The peaking La Nina in the equatorial Pacific and the demise of the positive Indian Ocean Dipole event (IOD, marked by warming of the western Indian Ocean) connived to generate rare winter conditions this year, says a research team led by Prof Toshio Yamagata, Programme Director, at the Tokyo-based Frontier Research Centre for Global Change (FRCGC).

HIGH PRESSSURE

Anomalous atmospheric convection in La Nina winters causes 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 causes the upper tropospheric westerly jets, carriers for WDs, to become weak and lie north of their normal positions. The number of WDs that manage to reach the Indian region gets curtained in this manner. The polar, northerly component of WDs (as against warm, moist southwesterlies) gets magnified in the bargain, setting the colder than normal winter over northwest India.

This is how the dry but colder than normal winter conditions established themselves over northwest India. But this cold spell has largely helped salvage the standing Rabi wheat crop in the region suffering from acute moisture stress during the dry winter.

TROUGH LINE

As far the China chill is concerned, the unusually strong Siberian high pressure zone introduced a corridor (trough line) across East Asia. Rich moist air was supplied from the tropical eastern Indian Ocean, including the Bay of Bengal region (possibly due to demise of IOD), as well as the western tropical Pacific (from warming due to La Nina).

An interesting feature was the positive phase of the Arctic Oscillation (AO) during this time of the year. The positive AO brings lower-than-normal pressure over the polar region, steering ocean storms northward, bringing wetter weather to northern Europe but drier conditions to areas such as Spain and the West Asia.

A positive AO phase is thus known to bring about warmer northern hemisphere winter conditions, but this was not the case for East Asia because of the existence of the above trough line. This in turn brought about unprecedented cold and wet winter conditions over northwest China.

More Stories on : Climate & Weather

Article E-Mail :: Comment :: Syndication :: Printer Friendly Page

Stories in this Section
Weeding out

Cold, dry winter a La Nina offshoot: Experts

Covering buys lift spot rubber prices

Bill for hiking cess on sugar introduced in Lok Sabha

Special sops sought for Barak Valley tea gardens

Prices rule firm at Coimbatore tea auctions

WGC to cross-list StreetTracks in Hong Kong, Tokyo

Cashew exports may rise on Vietnam woes

Bird flu: Poultry sector seeks loan waiver

Fall continues in pepper futures

Soya hits upper circuit

Labour shortage continues to bug coffee estates

Wage accord at Nilgiri plantations