Three years on, prolonged La Niña draws to a close

“During February 2023, below average sea surface temperatures prevailed and they weakened. Currently, they persist only in the central Pacific Ocean. The latest Niño – 3.4 index value is minus 0.2 degrees Celsius and the Niño – 1+2 index value at +1.1 degree Celsius. Collectively, the coupled-atmosphere system was consistent with ENSO neutral,” the NCEP’s final ENSO alert status issued on March 9 stated.

Scientifically, when the Niño – 3.4 index value falls below minus 0.5 degrees Celsius, it is termed as ENSO neutral. Oceanic Nino Index (ONI) is a value which guides meteorologists to declare either of these three events. This index of a region identified as Niño 3.4 (central equatorial Pacific) is the main indicator for declaring La Niña, El Niño Southern Oscillation (ENSO) and El Niño — the three oceanic events defined by the prevailing sea surface temperatures (SST) along the equatorial Pacific Ocean.

While La Niña refers to the abnormally cool SSTs, El Niño is the opposite and is linked to the significantly above normal SSTs in this region of the Pacific Ocean. ENSO is when the atmosphere and oceans are more dominantly affected by other climate drivers.

Both La Niña and El Niño, when combined with other climate drivers, directly affect the global weather. It may not affect all regions equally, but can lead to enhanced droughts, floods, cold or heatwaves.

Officials at the India Meteorological Department (IMD) and NCEP maintained that predicting the commencement of an El Niño event, expected later this year, will be ‘‘premature”.

(Anjali Marar is the Science Communication and Outreach Manager at the Raman Research Institute, Bengaluru)