Feature article
ENSO Update
by Ashmita Gosai, Stuart Burgess, and Dr Jim Salinger, NIWA
The now-decaying El Niño event began to affect the South Pacific climate from about the middle of 2002, after the sea surface temperatures (SSTs) in the tropical and eastern equatorial Pacific warmed to about 1°C above normal. These temperatures remained warm for the rest of the year, continuing into early 2003.
The climate of the Southwest Pacific had responded much as expected, with equatorial areas near the date line experiencing enhanced convection, resulting in three times average rainfall in Western and Eastern Kiribati extending south to Tuvalu. Suppressed convection over the Western Pacific resulted in below average rainfall in Australia and New Caledonia (Fig. 1). Parts of French Polynesia also experienced below average rainfall during the same period. Rainfall was generally about average for most of the other island nations in the region.
Most of the oceanic and atmospheric observations indicate that the current El Niño event in the tropical Pacific is weakening. The marked SST anomalies in the NINO3 and NINO4 region and the Southern Oscillation Index (SOI) have been weakening since December 2002. There has also been a noticeable breakdown of subsurface temperature anomalies since February 2003, and the easterly trade winds have resumed near normal frequencies.
There is a general consensus among most of the global El Niño Southern Oscillation (ENSO) forecast models that this event is likely to end by the early southern hemisphere winter.
The majority of global ENSO climate models are now predicting neutral conditions, as being most likely for the six months beyond June 2003.
Fig 1: The El Niño associated convective pattern (August 2002 through March 2003). Outgoing Long-wave Radiation (OLR) anomalies, in Wm-2 are represented in shaded areas. High radiation levels (yellow) are typically associated with clearer skies and lower rainfall, while cloudy conditions lower the OLR (blue) and typically mean higher rainfall.