{News} 080610 Dipole lends odds-on chance for surplus rain

Dipole lends odds-on chance for surplus rain

The Hindu Business Line, June 10, 2008

Vinson Kurian

Thiruvananthapuram, June 9 A rare third-in-a-row positive Indian Ocean Dipole (IOD) event unfolding in the equatorial Indian Ocean could just be the trigger the monsoon needs to fire on all cylinders and deliver more rain than what long-range forecasts seem to credit it with.
The Indian monsoon is known to thrive when it is rear-ended by a positive IOD, which arises from an anomalous warming of the West Indian Ocean in contrast with a cooling anomaly to the east. The pattern is reversed during a negative IOD.
“We may expect an above normal monsoon year but we should note that the evolution of IOD might be adversely affected by strong intra-seasonal disturbances,” Dr Toshio Yamagata and Dr Swadhin Behera of the Tokyo-based Frontier Research Centre for Global Change (FRCGC) told Business Line. The FRCGC is credited with the discovery of the IOD phenomenon.EXTREMELY RARE
It is extremely unusual that a third consecutive positive IOD has evolved this year following those in 2006 and 2007. The decadal change in the ocean condition, under the global warming stress, is an underlying factor for such frequent occurrences. This is similar to the “perpetual IOD”, which could have occurred several thousand years ago.
“As far as we know there is no such occasion in the past 100 years when we had three consecutive positive IODs. Anything closest that come to mind are the repeat IOD events of 1913 and 1914,” said Prof Yamagata and Dr Behera. Sea-surface temperature (SST) and rainfall data for the last 100 years were mined as part of an expansive study by FRCGC researchers.
“It seems the monsoon onset this year is earlier than the normal in several parts of India. The heavy rains that Mumbai and several parts in coastal Maharashtra are experiencing could be related to the evolution of the positive IOD,” said Dr Behera.
The IOD event does not endorse even spread of rains, spatial or temporal, as it turned out during the last year when northwest India ended up in a deficit even as the peninsular west and central India recorded excess rainfall. MONSOON ADVANCES
Meanwhile, the monsoon advanced into more parts of north Arabian Sea, south Gujarat, Maharashtra, Andhra Pradesh, Orissa, West Bengal, Bihar and the entire Bay of Bengal on Monday. The northern limit passed through Veraval, Nashik, Parbhani, Hanamkunda, Bhubaneswar, Sriniketan and Forbesganj.
Conditions are favourable for its further advance over more parts of Gujarat, Maharashtra, Orissa, Bihar and Jharkhand, and remaining parts of Andhra Pradesh and West Bengal, India Meteorological Department (IMD) said in its update on Monday.
A `low’ had sprung up over the northeast Arabian Sea off the Gujarat coast and had become well marked by the evening. An offshore trough extended from this system to the Kerala coast.
An upper air cyclonic circulation lay over northwest Bay of Bengal, off the Orissa coast. This too is expected to descend to lower levels to set up a ‘low.’ Fairly widespread rainfall has been forecast over east India during the next three days.
Heavy to very heavy rainfall is likely at a few places over Konkan, Goa and coastal Karnataka and isolated over Gangetic West Bengal, Orissa, south Gujarat, Madhya Maharashtra, Kerala and Lakshadweep over the next two days.
Extended forecast for two days from June 12 said that fairly widespread rainfall activity with isolated heavy to very heavy falls is likely along the west coast, Uttar Pradesh and central India.

Source: http://www.thehindubusinessline.com/2008/06/10/stories/2008061050771100.htm