Now playing in the Pacific: An Indian rain dance by La Nina

In short, the effects of El Nino, which oversaw India’s worst drought in 120 years, are diminishing. The ECMWF has predicted a decline in El Nino conditions in all four Nino regions in the Pacific from March 2003. The NOAA, in one of its forecasts made through its linear inverse model, has predicted the emergence of La Nina in the Pacific from mid-2003.

La Nina has always brought good rains to India. In the last 200 years, La Nina reigned 24 times. In 16 such La Nina years, monsoon rainfall in the country was above the average normal level. In the other eight years, the rainfall was in excess as per parameters then set by the India Meteorological Department (IMD).

In its latest forecast on the subsiding El Nino and the possible emergence of La Nina, NOAA said ‘‘a majority of the coupled model and statistical model forecasts indicate that near-normal conditions will prevail through September 2003.

However, there is uncertainty in this forecast, as some forecasts indicate the possibility of continued weak El Nino conditions while others indicate the development of La Nina conditions during the second half of 2003 (vide the linear inverse model). All such models have relatively low skills during the transition phases of the ENSO cycle.’’

Dr Sushil Kumar Dash of the Centre for Atmospheric Sciences (CAS) at New Delhi’s Indian Institute of Technology says that developments in the central equatorial Pacific Ocean are very important for Indian monsoons. ‘‘If El Nino conditions subside and the La Nina phenomena emerges, it will result in better rains in the country.’’ But Dr Murari Lal, also at the IIT, says the effects of cooling of Pacific waters will be felt in the next monsoon because there’s a time lag in the teleconnections between different predictors of Indian monsoon.

NOAA also has a note of caution: though El Nino, which began developing in the Pacific from February 2002, started declining from December 2002 by more than two degrees Celsius in the eastern equatorial Pacific, the SST anomalies remained greater than plus one degree Celsius in the central equatorial Pacific.

In this context, one should remember that Nino 3.4 and Nino 4 regions are located in the central equatorial Pacific and developments in these regions impact the Indian monsoon. The IMD has selected only Nino 3.4 region for assessment of the monsoon impact and not Nino 4 region which is closer to the Indian Ocean.

Dr Dash says it’s possible IMD’s waiting for the El Nino phenomena to subside in Nino 3.4 region which will allow it to say with confidence that the monsoon rains will be normal this year.

The IMD, he points out, has already sought time until mid-July to make a final forecast on the monsoon. ‘‘The hope for a normal monsoon hinges on the El Nino phenomena subsiding in Nino 3.4 and Nino 4 regions and the prospects of excess rain depend on the possible emergence of La Nina,’’ says Dash.

NOAA scientists Martin Hoerling and Arun Kumar, in a study on droughts in 1998-2002, highlighted how conditions in tropical oceans have substantial effect on atmosphere. The droughts which occured during 1998-2002 in US, southern Europe and Asia were linked to ocean conditions.

The cold SST in eastern tropical Pacific and warm SST in western tropical Pacific and Indian Ocean worked together to cause drought in the mid-latitudes. Warm conditions in the west Pacific in 1998-2002 had no precedent in the last 150 years.