Are El Nino Global SSTA Patterns Changing?

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03/12/2019, 2:40 pm EDT
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Summary: Modern-day El Nino episodes have a tendency to occur while many other parts of the global oceans are also warmer than normal. This observation is a large change from the previous strong El Nino episodes of 1982-83/1997-98 when most of the oceanic heat and influence on atmospheric climate was consolidated in the tropical East Pacific. Consequently, our understanding of El Nino climate rooted in the influence on the atmosphere by the 1982-83/1997-98 warm ENSO events is different for many regions.

Discussion: Are modern-day El Nino’s the same? According to the NOAA/CPC operational Nino index (ONI) the most intense El Nino episodes since 1950 occurred in 1982-83, 1997-98 and 2015-16. The warmest ONI for each episode occurred in December. Let’s take a look at global sea surface temperature anomalies (SSTA) on Dec. 1 of each intense El Nino provided by the Climate Change Institute at the University of Maine (Fig. 1-3).

The influence on global climate by the intense El Nino of 1982-83 was profound. The influence of El Nino 1982-83 caused (unexpected) weather disasters on each continent most famously in Australia, Africa and Indonesia where harsh drought occurred but also historic rainfall episodes in Peru.

During the following decade-plus the El Nino 1982-83 inspired the research community to the development of ENSO prediction processes and forecasts. And just-in-time as El Nino 1997-98 was just as strong as its intense predecessor. Once again widespread drought, historic rainfall and flooding and adverse effects on oceanic wildlife occurred although this time with some notice.

A 3rd intense El Nino formed in 2015-16. Once again profound drought emerged in Southeast Asia, Australia and Africa. However, there were differences from previous intense El Nino episodes such as failed rains in California and a dramatic wet South Brazil/drought Central Brazil regime.

The global oceans have turned somewhat warmer during modern-day El Nino episodes. The influence on the atmosphere is different from the 1982-83/1997-98 El Nino events. The primary change is the consolidation of tropical convection in the warm equatorial East Pacific region and influence on the global atmosphere during the 1982-83/1997-98 El Nino episodes compared to recent El Nino’s when tropical convection affecting the global circulation is not necessarily confined to the East Pacific.

For many regions modern-day El Nino should be a little different from the 1982-83/1997-98 benchmark El Nino episodes.

Is the influence of global oceanic warming hurting the evolution of the 2018-19 El Nino episode? The weak El Nino present now may have peaked in intensity late last year but without much engagement of the global atmospheric climate primarily due to the inability of tropical convection to organize and persist east of the Dateline to drive an El Nino climate.

Fig. 1: The first of 3 intense El Nino episodes since 1950 occurred in 1982-83. The peak strength was observed in December 1982. Pictured are the global SSTA on Dec. 1, 1982. Note how all of the oceanic heat is consolidated within the equatorial East Pacific El Nino zone.

Fig. 2: The second intense El Nino episode since 1950 occurred in 1997-98. Once again peak strength was observed in December. Pictured are the global SSTA on Dec. 1, 1997. Although the global ocean surface is not as cool as DEC-82 the repeat signature of ocean heat consolidation in the equatorial East Pacific El Nino zone is repeated.

Fig. 3: A third intense El Nino appeared in 2015-16. The peak of intensity occurred in December. Pictured are the global SSTA on Dec. 1, 2015. Note the much warmer global ocean surface in addition to the conventional accumulation of El Nino oceanic heat in the equatorial East Pacific.

Fig. 4: El Nino 2018-19 is out there but has struggled to organize. Once again the warmest SSTA of the weak El Nino episode (so far) was observed in late 2018. Similar to the stronger 2015-16 El Nino the global oceans are also quite warm.