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Monday, January 4, 2010

South Pacific Hot Spot

I’ve moved to WordPress.  This post can now be found at South Pacific Hot Spot
In replies to questions about the Hot Spot in the mid latitudes of the South Pacific, Figure 1…
Figure 1

…I’ve been posting a copy of the temperature anomaly correlation maps from Trenberth et al Trenberth et al (2002) "Evolution of El Nino–Southern Oscillation and global atmospheric surface temperatures", Figure 2:

Figure 2

As noted in Trenberth et al (2002), the evolution of ENSO and the responses of the global oceans to ENSO events undergo periodic changes. The Trenberth et al (2002) correlation maps for the periods of 1950 to 1978 and of 1979 to 1999 do not necessarily reflect the current state of the oceans. The 1997/98 El Nino discharged and redistributed a substantial amount of heat from the tropical Pacific, and the 1998/99/00/01 La Nina recharged that heat, so the global oceans are naturally warmer than they were before that “El Nino of the Century”. Are the global oceans responding differently in the years after the 1997/98 El Nino than they were before it? It appears so. As you will see, the hot spot in the central mid latitudes of the South Pacific appears to be a phenomenon that appears regularly after 1997/98 El Nino, while its appearance was unusual before it.


Keep in mind that the maps of the globe are rectangular projections of a sphere, so they distort distances at higher latitudes. A number of degrees longitude at the 40 degrees latitude are approximately 76 % of the same number of degrees at the equator, and at 50 degrees longitude, the percentage drops to 64%. If you’d like to calculate the surface area of the hot spot and compare it to the area of warming in the tropical Pacific, you can use the NOAA Latitude/Longitude Distance Calculator to help approximate the areas:

If we define the South Pacific Hot Spot by the coordinates of 50S-40S, 150W-120W, the SST anomalies for December 2009 are unusually high. This is illustrated in Figure 3.
Figure 3

Because the hot spot is accompanied by areas of unusually cool waters, the SST anomalies for the entire South Pacific SST anomalies, Figure 4, are NOT outside the range of the expected response to an El Nino event.
Figure 4


Figures 5, 6, and 7 are South Pacific SST anomaly maps for the month of December from 1982 to 2008. Prior to the 1997/98 El Nino, the hot spot appeared once in 1991. After the 1997/98 El Nino, the hot spot appears with every El Nino.
Figure 5
Figure 6
Figure 7

Apparently, the heat that was released and redistributed during the El Nino of the Century and its subsequent La Nina impacted ENSO teleconnections. Is this a harbinger of something terrible? No. It’s simply an indication that the response to ENSO events is different in one location after that Super El Nino. There is no apparent difference in the basin-wide response.

OI.v2 SST Anomaly data and maps are available through the NOAA NOMADS webpage:


kuhnkat said...

What is your opinion of the possibility that the active volcano reported in this warm area is contributing to the increased anomaly??

Bob Tisdale said...

kuhnkat: If you're referring to the post from earlier this year at WUWT, the author of the post missed the location of the hotspot and volcano by a chunk of miles. If not, what active volcano?

kuhnkat said...

Yup, I am. I take it a chunk of miles is over 1000?

kuhnkat said...

I went back and did the background check I should have done first.

There were eruptions off Guam and Tonga during that time period. I also checked Ocean Current maps and it would appear unlikely that the Tonga eruption, the closer one, would have had a significant impact on the gyre anomaly alone.

hswiseman said...

Hi Bob,

How deep do these anomalies penetrate? Are we seeing some type of closed cell ocean circulation between the hot and cold anomalies? (BTW,I really appreciate the relentless scientific orientation here. I really am sick of politics in all its forms).

Bob Tisdale said...

hswiseman: You asked, "How deep do these anomalies penetrate?"

Luckily, the cross sections presented in the ECMWF Meridional Secions...
...provides a look at 140W. They appear to penetrate a little more than 50 meters.

hswiseman said...

It almost looks like the more boyuant warm pool is trapped between two columns of more dense cooler water on each side. The warm pool temperature is fairly consistent despite the change in depth, indicating perhaps that the warm water is well mixed?


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