Status May 23

All three runs streams are progressing forward, 5 months in, approximately. However, as some folks here were making corrections a few weeks ago there were some unusual reports in the sonde data. Further investigation has found a problem that is fairly easily correctable. Actually there are two problems, and they change in time.

Starting around 1988, the actual launch time isn't being considered, just the synoptic time of the launch. From 1988-1992, this occurs in less than 1% of the launches at any given synoptic time. After 1992, the rate increases to around 10-15%. The consensus is that the impact to the 1989 MERRA stream is small, and we can have this fixed by the time we cross 1992. However, in 1992, a more serious problem occurs. Then, some sondes are not labeled correctly as to their manufacturer. This then affects whether the radiation correction for certain sondes is called, and the radiation correction is important to handle correctly. This occurs at a rate of about 15% at any given synoptic time, also a fairly large number. Again it can be corrected for the 1989 stream, before it gets serious.

The 1998 stream is another matter. Both of these problems are occurring at a rate of about 15% per synoptic time in January 1998 and on. So, the data we have processed for the 1998 stream has a flaw than needs to be corrected. In order to stay timely with the MERRA processing, we will continue the 1998 stream to 1 July 1998, at which time the fixed sonde data will be implemented. The Jan - Jun 1998 data processed so far will not be released. Instead, we will continue the 1989 stream to recover this period, and there will be overlap through 1998 to ensure that the transition of streams is as smooth as possible.

A word about the source of this error. We are using recently reprocessed sonde data from NCEP, and working with NCEP closely on monitoring and quality controlling this data. This is the data set that would also go into the NCEP CFSRR, but is not the same as has been used in previous reanalyses.

So in summary, there is no impact on the 1979 data stream. The extremely small number of launch time errors early in the 1989 stream are considered to be nominal, and the sonde data will be fixed as soon as possible. The 1998 data from Jan - Jun must be redone. The fix to the data will be implemented on Jul 1998.