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Monday, September 1, 2008

ERSST.v3 Version of Southern Ocean SST Anomaly


I’ve been investigating the ERSST.v2 version of the Smith and Reynolds SST data for so long I’d forgotten I’d never checked the latest version (ERSST.v3) to see what the update for the Southern Ocean looked like. I’m glad I checked. Smith and Reynolds have made significant progress compiling data for the Southern Ocean.


Figure 1 illustrates the ERSST.v2 version of the Southern Ocean SST anomaly data from January 1854 to May 2008. I’ve posted it and discussed it a number of times in this series.
Figure 1

The latest version, ERSST.v3, is significantly different, as shown in the comparative graph, Figure 2. The ERSST.v3 data begins January 1880 and ends April 2008, where the ERSST.v2 data begins in January 1854 and continues to be updated. That aside, the smoothed and dampened curve of the old data set prior to 1960 has been replaced with data that gives long-term trend information, including a significant drop in SST during the late 19th to early 20th centuries.
Figure 2


Figure 3 shows the raw ERSST.v3 Southern Ocean SST anomalies from January 1880 to April 2008. On the webpage that serves as my source, there have been no updates since then. There are multiyear gaps in the data during the 1910s and 1940s, a result, apparently, of the World Wars. There are also smaller gaps that are impossible to discern in the graph.
Figure 3

When the data is smoothed with a 37-month running-average filter, the gaps disappear and the trends become clearer. Refer to Figure 4. Overall, Southern Ocean SST anomalies dropped from 1880 to 1920, but within that timeframe there was a short and substantial rise in SST anomalies from around 1892 to 1898. SST anomalies rose from the 1920 to the early 1980s, where they peaked. Southern Ocean SST anomalies have been dropping ever since. Does this infer an oscillation with a frequency of 120 years? Or is this variability a reaction to other drivers?
Figure 4

It must be remembered that the Southern Ocean mixes with the Atlantic, Indian, and Pacific Oceans and that, in one hypothesis of long-term ocean circulation, the bulk of Thermohaline Circulation (THC) upwelling occurs in the Southern Ocean.

A good starting place for more information about THC is Wikipedia.

Figure 5 shows the short-term Southern Ocean SST anomaly data, from January 1978 to April 2008. Even with the volatility of SST, the downward trend is visible from the 1980s to present. What does catch the eye is the spike that occurs 4 years before the 97/98 El Nino.
Figure 5

In Figure 6, I scaled NINO3.4 data with a multiplier of 0.35 and shifted the Southern Ocean data back in time by 48 months so that the spike in the Southern Ocean SST anomaly data aligned reasonably well with the 97/98 El Nino. While it appears there might be interaction between the Southern Ocean and the El Nino/Southern Oscillation, the absence of cause and effect for the 82/83 El Nino and the 87/98 La Nina implies there is something else that interacts with NINO3.4 SST.
Figure 6


Smith and Reynolds Extended Reconstructed SST (ERSST.v2) is available through the NOAA National Operational Model Archive & Distribution System (NOMADS).

The more recent version of the Smith and Reynolds Extended Reconstructed SST (ERSST.v3), along with land surface temperature and combined (land + ocean) surface temperatures, are available in various latitudinal bands at:
Don’t let the PDO in the address bother you. There’s much more there. The overview for the update is here:

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