Most of the global weather agencies are now speculating a neutral ENSO in the second quarter of 2016 and possibly a weak La Nina thereafter.
A repeat El Nino is assessed as very unlikely.
Click here to read, What is La Nina
Warmer or colder than average temperature in one part of the world can influence weather around the globe. El Nino and La Nina are opposite phases of what is known as the El Nino – Southern Oscillation (ENSO). La Nina and El Nino are the cold and warm phases of ENSO respectively and have large potentials to impact weather activity on a synoptic scale. ENSO cycle is governed by the fluctuations in temperature between the ocean and atmosphere, in the east central equatorial Pacific Ocean.
Click here to read, What is El Nino
The deviation from the normal sea surface temperature (SST) can trigger changes in the ocean dynamics which in turn impacts global weather and climate. Truly speaking, it is not only the SST, but the ocean mean temperature (OMT), which is a more realistic and a better representative of ocean heat content that governs the atmospheric circulation. As of now, neither the SST has relaxed nor have the ocean heat anomalies declined substantially.
During January-March 2015, a significant sub surface warming across the eastern Pacific was observed. Thereafter, during August-September positive anomalies decreased but again rose in October. A falling trend was noticed in November-December. The temperatures showed signs of an increase in January again and this may lead to another peak shortly during the spring.
The ocean indices over the entire East and Central Pacific continue to be fairly high and a sudden collapse seems unlikely. The propensity of oceans to retain heat energy will restrict any rapid loss or drop in the oceanic energy. The capacity of oceans to conserve energy is phenomenal and decline is invariably gradual. The past records of oceanic nino index (ONI) for overlapping quarters suggest a maximum drop by 0.5°C from one to the next. With the existing high positive anomalies of 2.5°C, even reaching a neutral state is a daunting task and possibly is going to be a long drawn process.
Here’s a look at the ONI Index for overlapping quarters of 2015.
Out of 26 El Nino episodes since 1900, around 50% have been followed by a neutral year and 40% by La Nina. Two successive El Nino’s, though not many, are also on record.
Since 1950, the longest duration of El Nino occurred from August 1986 to March 1988. The current event has already lasted for 12 months from February 2015 till date (January 2016). Similarly, the longest La Nina on record is for 23 months, from June 1998 to April 2001.
Must Watch: NOAA explains El Nino and La Nina phenomena
In case of prolonged La Nina conditions, the Monsoon rains are found better in the years when La Nina commences as compared to the following year.
Occurrence of El Nino is invariably linked with poor Monsoon rains but exceptions are there on record. Likewise, La Nina has been associated with above normal rains, though not always. Unlike a fairly strong correlation between El Nino and weak Monsoon rains, La Nina does not find a convincing cause-effect relationship.
El Nino models have been helped by the development of satellite and network of buoys which can track the ocean thermal profile. But then, how well do our current weather and climate models perform in representing the tropical atmosphere’s response to El Nino?
The decommissioning of older satellites and ingesting of newer satellite data in the data assimilation system is bound to bring some changes in the initial state of models. Nevertheless, over a period of time the changes get integrated with the model dynamics and get stabilized.
However, when it comes to studying impact of an evolving El Nino, the February-March data lacks credibility and is marred by the ‘Spring Barrier’. As of now, it is too early to speculate a bouncy Monsoon on account of La Nina. The best bet at this stage could be a neutral ENSO. For a more authentic and comprehensive Monsoon forecast, one will have to wait till April.
Image Credit - NOAA