El Niño/Southern Oscillation (ENSO)

El Niño/Southern Oscillation (ENSO)

During January, El Niño conditions were wellestablished in the equatorial Pacific. Equatorial sea surface temperature anomalies weakened a little in the NINO3 region in response to weakened Equatorial westerly wind anomalies. In NINO4 SSTs changed only slightly where the westerly wind anomalies persisted. In January, the NINO3 SST anomaly was +1.4°C and the NINO4 anomalies was +1.6°C (3–month NDJ means were +1.5°C and +1.6°C respectively). Upper-ocean equatorial heat content anomalies were positive east of the Date Line, and showed signs of weakening as the easterly trades strengthened later in the month. The large positive subsurface temperature of above +4°C east of 130°W that existed in December has also weakened, and this indicates that El Niño has peaked and is beginning to weaken.

The SOI for January was –1.1 (NDJ mean –1.0). Tropical OLR anomalies in January showed strongly enhanced convection across the Equatorial Pacific from near the Date Line towards Papua, northern Australia and Indonesia. The extensive area of convection that was present during January was probably due to a combination of the classical El Niño convective pattern and an MJO event that passed across Indonesia and into the Pacific. The MJO event is expected to stall in the western Pacific during the first half of February, with suppressed convection spreading over the eastern Indian Ocean/western Indonesia regions. The MJO influence may account for a slow weakening in the SOI over the past two months. The TRMM ENSO precipitation index was –0.0 for the 30 days to 25 January.

The global climate model ensemble assessed by NIWA show dynamical models (and all but one statistical model) projecting warm conditions through to the end of April 2010, but all models show a weakening towards neutral conditions in autumn. The NCEP ENSO discussion from 7 January suggests a strong El Niño at present but it is expected to weaken and persist into the austral autumn. The IRI summary (21 January) indicates a 98% above 90% of continuing El Niño through February-April., before returning to climatological probabilities in July–September. 

Sea surface temperature anomalies (ºC) for January 2010

Mean sea surface temperatures (ºC) for January 2010