The 2015-16 El Nino that sparked off record temperatures globally has finally come to an end during the mid-month of May. The El Nino, which was considered as strongest ever on record after 1997-98, has caused some extreme events across the globe during it’s period as few parts of the world witnessed extreme drought, and few parts of the world were affected by relentless rains and flooding. However, the period has come to an end as we’ve entered into the neutral state of the ENSO (El-Nino Southern Oscillation).
During this EL Nino, Indian summer monsoon was badly affected for second consecutive year leaving many place under water scarcity. Due to the poor monsoon, the relentless heat-waves during period of March-May has even worsened the situation across those areas claiming many people’s lives. However, prospects of an above-average monsoon looks good for India in 2016 as the period of El Nino has been officially declared over.
The biggest question is whether we’ll slip into a La Nina this year, which is what we’re anticipating right now. While there’s so much divergence among models on when La Nina would officially would take over, the depth of the Pacific Ocean is hinting for a possible La Nina conditions would establish by this meteorological summer (Jun-Aug).
SUB-SURFACE TEMPERATURE ANOMALIES
Going by the above chart, you can see ~-4C departures in the Central Pacific at about depth off 100-150m which will push over to surface in coming months, & with this amount of cooler anomalies, we could mostly see the flip to La Nina around late summer/early fall.
Also, looking at the monthly graph of the Nino 3.4 Sea surface temperature anomalies, it has been extremely consistent with the decline of El Nino. After almost two years, we have seen Nino 3.4 region Index flipping to negative which is a signal of a developing La Nina in the Pacific.
In addition, when doing a comparative study of all the NINO regions with respect to 1997-98 El Nino, which was previous Super El Nino period, 2015-16 was much stronger in Central Pacific than East Pacific.
SOUTHERN OSCILLATION INDEX
Looking at the Southern Oscillation Index (component of ENSO), it has finally flipped to positive mode after a year which also conveying that La Nina is in making in the tropical Pacific ocean.
For a comparative study with 1982-83 & 1997-98, which were the previous two Super El Nino years, the SOI in 2015-16 never dipped into a strong negative phase compared to 1982-83 & 1997-98, thanks to strong interference of MJO which increased the tropical convection over Indian ocean that in turn boosted the trade winds across Pacific. This clearly conveys that 2015-16 Super El Nino falls behind the 1997-98 El Nino strength.
Coming to a consensus by looking at all the factors, we should slip into a La Nina by late summer/early fall in 2016. This will play a major role in enhancing the Indian monsoon and much of India is likely to receive above normal rainfall aside North-East portion.
NORTH PACIFIC & ATLANTIC OCEAN EVOLUTION
We have seen so far the status of the tropical Pacific (ENSO) & the likelihood of La Nina during the late summer/fall, but that’s not the only factor that is going play role in the summer/fall.
The decadal variability of North Pacific & Atlantic ocean has started to show signs of transition which may have impact on global circulation during 2016.
When you look at this sea surface temperature anomalies, watch out for the cold pockets of waters over North Atlantic Ocean (white arrow) progressing south. The cold waters over North Atlantic has been there for last couple of years, and may move down towards tropical region at some point, which may switch the Atlantic Decadal Variability (AMO) to a negative phase. This pattern may have an influence on global weather, but the timing of that switch is going to be critical. It may not happen so soon in near future, but for decadal trend something to keep an eye on.
Also keep an eye on the cooling taking place in the North-East Pacific (Red circle) which is an indication of a flip in decadal variability of North Pacific (Pacific Decadal Oscillation) likely this fall. This trend is likely to happen given the conditions that are expected across Tropical Pacific ocean and this pattern will enhance the monsoon across the Asian continent. At the same time, this can have large scale impact on temperatures across mid-latitude region with increasing warmth.
This cooling of North Pacific & Atlantic ocean needs to be monitored not only for impacts on weather across the globe, but also for the state of tropical Pacific.
When both show signs of flip to cooling phase, La Nina would be there to stay for more than couple of years & frequency of El Nino events may reduce.