{News} 090322! Model forecasts indicate normal monsoon this year

Model forecasts indicate normal monsoon this year

Vinson Kurian
Thiruvananthapuram, March 22 The International Research Institute (IRI) for Climate and Society at Columbia University has forecast normal to slightly above normal monsoon for India during June to September this year.

This would be preceded by a spectacular pre-monsoon season, especially towards the East and northeast of the country, a comparative study of predictions by IRI and other models suggested.
The IRI has also predicted above normal temperatures for North India during the April-May-June quarter, which is crucial for ‘setting up the monsoon’. The land-ocean temperature differential is the driving force behind the monsoon.

BUSY NORTHEAST
The May-June-July quarter witnesses the onset of monsoon orchestrated by the Arabian Sea arm along the Southwest coast and the Bay of Bengal over the northeastern States.
IRI forecasts indicate a busy onset phase over the northeast, coming close on the heels a successful pre-monsoon season. Nagaland-Manipur-Mizoram-Tripura, Assam and Meghalaya, along with adjoining Bangladesh and Myanmar, may benefit.

But the onset along the southwest coast (over Kerala) is being seen as a more sober affair, though a blow-up of rains is indicated for coastal Karnataka and the Konkan coast.
June-July-August would see normal rains all over the country. During the last year, the rains had failed this crucially important phase leading to destruction of the sugar and cotton crops.
Independent forecasters warned that the weak but prevailing La Nina conditions in the equatorial Pacific and a still evolving Indian Ocean Dipole (IOD) could combine to totally undo the best forecasts.

In a La Nina, ocean temperatures cool down in the equatorial and equatorial-east Pacific while a corresponding warming anomaly propagates to the west. Associated convection and storm development are traditionally found to favour a good Indian monsoon but without any direct cause-effect relationship.

An IOD refers to the see-sawing of temperatures in the West and East Indian Ocean, and has a more immediate effect on the performance of the monsoon.

A positive IOD (warming anomaly in the West Indian Ocean) amplifies the performance of the monsoon, as has been the case during the last three years, a rare occurrence by itself. Excess showers over the west coast and adjoining central India is a signature feature associated with a positive IOD.

Both the Indian Ocean and the equatorial Pacific oceans are being scanned for possible signs of season-altering trends with respect to specific parameters.

In any case, the IRI has ventured to suggest that the four-month season would end in a flourish during the last quarter of July-August-September. The west coast and adjoining central peninsula extending to some parts of north and northwest India are expected to witness excess rains during this phase.

Mr Jing-Jia Luo, Senior Scientist at the Tokyo-based Climate Variations Research Program Frontier Research Centre for Global Change, informed Business Line that the current La Nina may persist until the year-end.

Mr Luo has also forecast that a negative IOD may spring up during the second half of the year. Unlike a positive IOD, a negative IOD is usually weak and might have less influence on monsoon.
Again, the net effect of La Nina-negative IOD might depend on the strength of each signal. If the La Nina were to persist, it would have a positive impact on the monsoon.

“While current trends are suggestive of a weak La Nina lasting until the end of the year, it is advised that we wait for another month just to make sure,” he added as a word of caution.
“Model forecasts for June to August do show more rainfall for many parts of India, in particular, western India. Low-level wind behaviour too rules out a weak monsoon. To sum up, I would expect stronger than normal monsoon this summer,” Mr Luo said.

Source: http://www.thehindubusinessline.com/2009/03/23/stories/2009032350150400.htm