In an attempt to better understand climate change in the Pacific and Indian Oceans, I have begun to make videos like the one I will present here, which documents sea surface temperature (SST) in the North Pacific. Each graph in the video is a SST time series of a segment of ocean 2 degrees wide, stretching from the equator to 60N (or wherever that segment hits land). As the movie progresses, the graphs move Eastward.
Orginally, my intent was to show SST from 1854 to the present. However, I found that variation from 1974 to the present sheds a lot of light on the nature of what we consider to be the El Nino/Southern Oscillation (ENSO).
Click here for the video. You will have to watch it a few times.
It seems to me that three “true” El Nino events took place since the climate shift of 1976. 1982/3, 1986/7, and 1997/8.
- The 1982/3 event was countered by the eruption of El Chichon. Because of this, no extra heat entered the system, and no La Nina followed the event.
- The 1986/7 event was associated with heat input into the system, and some of that heat entered the North Pacific via the Kuroshio Current. This heat that was recyled through the North Pacific re-appeared in the tropics as the El Ninos of 1991-1995.
- The 1997/8 event was also associated with heat input into the system. The same process occured as with the 86/7 El Nino, resulting in the El Ninos of 2001-2006.
- All of this was superimposed on falling tropical temperatures, recovering from the climate shift of 1976.
We see the long-term influence of the 86/7 ansd 97/8 El Ninos in the “humps” of temperature from 1989 to 1997 and from 2000 to 2008. These “humps” are also apparent in the ENSO curve. After the initial El Nino event in the equatorial Pacific, heat moved into the West Pacific as a spike, spread out into the West/Central Pacific creating a step-change, and continued to spread into the Central/Eastern Pacific at a variable rate, creating a hump. These humps then influenced the ENSO curve in the equatorial Pacific.
The blue curve represents the underlying shape of ENSO, driven by the “real” El Nino events, and shown in the North Pacific. It is also apparent that the residual heat from the 1986/7 El Nino my have bolstered the 1997/8 El Nino.