El Nino is a coupled interaction of the atmosphere with the ocean resulting in warming of sea surface temperature (SST) in the Central and East Pacific Ocean. The El Nino lasts for about 9-12 months, but there are exceptions of overstepping this threshold and go on for even 2 years at a stretch. Nino indices are measured over an area of 12 million sq km. El Nino results slowing down of trade winds and sometimes even reversal in the equatorial belt, which causes a shift in the weather pattern across the globe.
Warming of the Pacific before the arrival of Indian Monsoon is not taken kindly. Even a faint presence of El Nino can corrupt the Monsoon rains. It has strong linkages with the time of onset, intensity, and overall performance of seasonal rains. The table shows the trend of Nino indices over the last few weeks:
These indices depict positive values, means warming in all the sections and mostly above the threshold mark of 0.5. These could be biased because of the spring barrier but consistency over the last 5 weeks or even longer can not be ignored.
The Oceanic Nino Index (ONI) is based on SST departures from average in the Nino3.4 region and is a principal measure for monitoring, assessing, and predicting ENSO. It is defined as the three- month running- mean SST departure in the Nino3.4 region. To be classified as El Nino episode, this threshold must be reached or exceeded for a period of at least 5 consecutive overlapping 3-month seasons. The table shows the trend of ONI:
The Pacific is warmer than the average for fairly long. The most recent value is +0.5degC. Actually there have been four consecutive positive values of the same magnitude. And looking at the trend the fifth one is also going to be + 0.5 or more. Technically speaking five readings in a row exceeding the threshold mark qualifies for an El Nino episode. But the seasonal projection suggests the El Nino index reaches nearly zero by June.
For a timely onset and a good start, these +ve ONI values literally need to collapse and it has happened on a few earlier occasions. But as of now, we keep our fingers crossed. Eagerly waiting for the spring barrier to get over to instill confident and reliable forecasts.
