>In replies to questions about the Hot Spot in the mid latitudes of the South Pacific, 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:
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.
THE SIZE OF THE HOT SPOT
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:
HOT SPOT SST ANOMALIES
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.
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.
PAST DECEMBER SST ANOMALY MAPS
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.
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: