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Friday, April 17, 2009

A Closer Look At The ERSST.v3b Southern Ocean Data

I’ve moved to WordPress.  This post can now be found at A Closer Look At The ERSST.v3b Southern Ocean Data
The time-series graph of the ERSST.v3b SST anomaly data for the Southern Ocean, Figure 1, is unique. It clearly shows that Southern Ocean SST anomalies were higher in the late 1800s than they were at their late 20th century peak. Note also how Southern Ocean SST anomalies have been dropping since the early 1990s.
Figure 1

But where does the unique shape come from?


Figure 2 is a comparative graph of the Southern Ocean SST anomalies, where the data has been divided by the approximate southernmost longitudes of the three major oceans: Atlantic (90S-60S, 70W-20E), Pacific (90S-60S, 145E-70W), and Indian (90S-60S, 20E-145E). It’s clear that the major variations originate south of the South Pacific.
Figure 2

Figure 3 illustrates the Southern Ocean SST anomalies south of the South Pacific without the distraction of the other datasets.
Figure 3

Dividing the data of the Southern Ocean south of the Pacific, Figure 4, illustrates that the majority of the variability lies in the East Central (90S-60S, 145W-110W) and East (90S-60S, 110W-70W) segments.
Figure 4

If those two sections of the Southern Ocean south of the Southeast Pacific are combined (90S-60S, 145W-70W) and compared to remainder of the data for the Southern Ocean (90S-60S, 70W-145W), Figure 5, two things stand out. First, the remainder of the Southern Ocean made a slow dip (from the late 1870s to the early 1930s) and rebound (from the early 1930s to the late 1970s). And since the 1970s, the SST anomalies for that major portion of the Southern Ocean have been dropping. Is the dip and rebound and recent decline part of a ~100-year oscillation? Second, something adds to the apparent natural oscillation in the Southern Ocean south of the Southeast Pacific, which represents about 21% (75 deg longitude/360 deg longitude) of the Southern Ocean, to create the additional variability.
Figure 5

And the logical contributor to the variability of the Southern Ocean south of the Southeast Pacific would be ENSO. Figure 6 compares scaled NINO3.4 SST anomalies to those of the Southern Ocean south of the Southeast Pacific. The timing of the perturbations agree for the most part. At other times, that portion of the Southern Ocean appears to respond to some other forcing.
Figure 6

Figure 7 illustrates the SST anomalies of the Southern Ocean south of the South Atlantic and Indian Oceans. Note how the two datasets appear to modulate out of sync at times. Is this evidence of Antarctic Circumpolar Waves? Refer to:
Figure 7

Refer back to Figure 2. After 1910, note how two of the three datasets appear to vary in unison, while the third opposes them. There are occasions when all three vary in sync, but they occur less often.

As an additional reference, Figures 8 and 9 are the individual SST anomaly graphs for the Southern Ocean south of the South Atlantic and Indian Oceans.
Figure 8
Figure 9


We often hear that global warming is causing the Wilkins Ice Shelf to break free of Antarctica. Refer to Figure 10. Many times the article will note that the local Southern Ocean SST anomalies have risen for the past 50 years. What they fail to mention are:
-SST anomalies for that location show a negative trend over the past 150+ years,
-SST anomalies in that area were higher in the late 1800s than they were in the late 1900s, and
-SST anomalies have dropped significantly since the late 1990s.
Figure 10


ERSST.v3b SST anomaly data is available through the KNMI Climate Explorer website:http://climexp.knmi.nl/selectfield_obs.cgi?someone@somewhere


Alan Cheetham said...

I recently wrote an article about the Wilkins Ice Shelf (see: http://www.appinsys.com/GlobalWarming/AntarcticWilkinsIceShelf.htm). The last plot in your article - the plot of the Wilkins area was curious to me -- so I plotted the same area at the NOAA ESRL page and get a very different result (see: http://www.cdc.noaa.gov/cgi-bin/data/timeseries/timeseries.pl?ntype=1&var=SST&level=2000&lat1=-65&lat2=-80&lon1=-80&lon2=-60&iseas=1&mon1=0&mon2=11&iarea=0&typeout=2&Submit=Create+Timeseries)

Unknown said...

Thanks for your careful research. Since I have learned so much about our oceans from reading your posts on WUWT, I check your blog a number of times a week. The charts are amazing.

Bob Tisdale said...

Alan Cheetham: Your graphs are of annual averages of Jan-Feb-Mar (Summer) SSTs, while the ones I illustrated are monthly SST anomalies smoothed with a 37-month filter. They may also be two different datasets.

Jeanette: Thanks.

Alan Cheetham said...

Hi Bob:

No - I don't mean the plots in my article compared to yours - I mean this one, (Jan -Dec covering the same area as yours): http://www.cdc.noaa.gov/cgi-bin/data/timeseries/timeseries.pl?ntype=1&var=SST&level=2000&lat1=-65&lat2=-80&lon1=-80&lon2=-60&iseas=1&mon1=0&mon2=11&iarea=0&typeout=2&Submit=Create+Timeseries

Bob Tisdale said...

Alan Cheetham: The NCEP SST Reanalysis graph of the 80S-65S, 80W-60W grid is interesting. After the shape of the curve, the first thing I noted was the scale. They're showing SSTs at -16 to -19 deg C, but sea water freezes at approx -1.8 deg C, so that's a problem.

The NCEP graph also made me curious, so I plotted the annual SSTs (not anomalies) of the ERSST.v2, ERSSST.v3b, HADISST, and OI.v2 SST datasets for the 80S-65S, 80W-60W area.

1854 to 2008 is here:

1950 to 2008 is here:

The NCEP data resembles the HADISST data after 1970, but bears no likeness before then.

The ERSST.v3b is the latest from the NCDC and they eliminated the satellite data from it because it was influencing it in ways that users didn’t like. HADISST and OI.v2 SST both use satellite data to supplement buoy and ship data.

Whose dataset does one believe?

HR said...

Hi Bob,
I don't know if your still taking comments on this given it was posted so long ago but here goes.

I got here in a roundabout way from looking at The State of The Climate 2009 and wanting an image of the Southern Ocean SST. I was looking for something to compare the N. Atlantic record in the above doc. You sort of confirmed for me that the N amd S oceans seem to run with a seesaw effect in their SSTs.

On a side note figure 5 and 6 got me thinking. You've identified an underlying 100 year ossilation in the Southern Ocean. If you subtracted that osillation from the Southern Ocean south of the Southeast Pacific anomoly (for example red - green in Fig5) and then compared the resulting data to the ENSO index (as in Fig6) it looks to me like you'd get an even better fit with the ENSO index.

I read your post with interest, it always frustrates me that many discussions of climate seem to reduce every changing metric to one factor. It's good to see somebody looking at the fasinating natural variability. Thanks


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