January 21, 1998
In response to a question by Dr. Rupa Kumar (visiting scientist at ENM/URF/UMT Meteo France) concerning the large 1997 Indian monsoon rainfall, Bob Kistler found a problem with our handling of the Indian station data since March 1997. These analyses are not "wrong" but use more Indian station data than intended. Preliminary plans are to redo the analyses starting from March 1997 with an expected completion date in February 1998.
CDAS/Reanalysis did not use all the Indian station data (i.e., stations were "blacklisted") which was NCEP practice when Reanalysis was developed. Since then, operational practice has changed so that Indian stations are not blacklisted and PAOBS are not used. In March 1997, CDAS's GTS decoder had to be changed to the new operational decoder because NCEP's mainframes were removed from service. Through an oversight, the Indian data were not blacklisted for processing by CDAS. This oversight will be corrected. At present, there are no plans to add PAOBS decoding to the new decoder.
The effect of using the "blacklisted" Indian stations was to drastically increase the Indian monsoon precipitation. According to Dr. Kumar, the assimilation's too low precipitation became too large. Removing the "blacklisted" stations is necessary for the sake of temporal continuity over the Indian subcontinent. On the bright side, Dr. Kumar found the interannual variability was "reasonably well captured" (about 0.8 correlation between the total Indian JJAS precipitation anomalies and Reanalysis for the years 1974-1996.)