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Wednesday, May 20, 2009

Update of Recent Differences Between GISS and NCDC SST Anomaly Data And A Look At The Multiple NCDC SST Datasets

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THE AVAILABILITY OF ERSST.v2 DATA

In a post at Climate Audit “Bob Tisdale on SST”, Steve McIntyre noted that NOAA has stated, regarding their ERSST data, that “V3b is now the official version. V2 will no longer be updated. It will still be available in our subdirtectory /Datasets/noaa.ersst/V2/'”
http://www.cdc.noaa.gov/data/gridded/data.noaa.ersst.html

There is no date on the notice from NOAA, and it has been my understanding for a few months that ERSST.v2 would no longer be updated.

--BUT--

The ERSST.v2 data available through the KNMI Climate Explorer is current through April 2009. Go figure.


Thanks again to Steve McIntyre.


THE REASON FOR DELETING THE SATELLITE DATA FROM THE ERSST.v3 DATA

Reynolds, Smith, and Liu gave the reasons for removing the satellite data from ERSST.v3 data as, “In the ERSST version 3 on this web page WE HAVE REMOVED SATELLITE DATA from ERSST and the merged product. The addition of satellite data caused problems for many of our users. Although, the satellite data were corrected with respect to the in situ data as described in reprint, there was a residual cold bias that remained as shown in Figure 4 there. The bias was strongest in the middle and high latitude Southern Hemisphere where in situ data are sparse. THE RESIDAL BIAS LED TO A MODEST DECREASE IN THE GLOBAL WARMING TREND AND MODIFIED GLOBAL ANNUAL TEMPERATURE RANKINGS.” [Emphasis added.]

The link for that quote is here:
http://www.ncdc.noaa.gov/oa/climate/research/sst/papers/merged-product-v3.pdf

So, how much did the removal of the satellite data change the appearance of the Southern Ocean data? Figure 1 is a comparison of the ERSST.v3 and ERSST.v3b versions of the Southern Ocean SST anomalies from January 1970 to April 2008, smoothed with a 12-month running-average filter. It clearly shows the change to the annual temperature rankings of the Southern Ocean.

http://i40.tinypic.com/2zg9i5h.jpg
Figure 1

Figure 2 is a long-term comparison of the ERSST.v3 and ERSST.v3b SST Anomaly data for the Southern Ocean, smoothed with a 37-month filter. With the smoothing, the ERSST.v3 version has been cooling since the 1980s, and in the ERSST.v3b version, the cooling was delayed for more than a decade. There also appear to have been some other adjustments made to the earlier data that would not have been a part of the satellite data fix.
http://i40.tinypic.com/2rw6sg7.jpg
Figure 2

SOURCES

The ERSST.v3b SST anomaly data is available through the NCDC’s ERSST.v3 webpage:
http://www.ncdc.noaa.gov/oa/climate/research/sst/ersstv3.php
Link to the available datasets:
ftp://eclipse.ncdc.noaa.gov/pub/ersstv3b/pdo
I used this dataset for this post:
ftp://eclipse.ncdc.noaa.gov/pub/ersstv3b/pdo/aravg.mon.ocean.90S.60S.asc

I used the obsolete ERSST.v3 I had on file for the comparison graphs.

2 comments:

steve said...

Bob, KNMI is getting its data from here (V2 shows an update on May 11, 2009)

ftp://ftp.ncdc.noaa.gov/pub/data/ersst-v2/

Bob Tisdale said...

Steve: Thanks for the link.

If I had to guess, I'd say there are a number of researchers using the ERSST.v2 data, and they complained when NCDC failed to update it. Hence the delay in the update to the 11th, where the ERSST.v3b data gets updated on the 3rd of each month.

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The Smith and Reynolds SST Posts DOES NOT LIST ALL SST POSTS. I stopped using ERSST.v2 data for SST when NOAA deleted it from NOMADS early in 2009.

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