Status June 5

We've had some good news and bad news. The good news is that efforts by the analysis group to revise the error statistics have had the expected positive impact on a systematic zonal wind bias in the tropics at upper levels. Further, the adjustments in the convective parameterizations by the model group have held up through this testing, and precipitation looks be reasonable compared to other reanalyses and observation data sets at the monthly time scales.

The bad news is that the "saw tooth" problem persists, but progress is being made in understanding it. In one of the data sweeper runs, we find that the analysis is reasonable, through Dec 2000, then the sawtooth begins in January 2001. This is at the same time NOAA 16 data begins to be used in the input data stream. Presently, the satellite bias corrections used in the system are being reexamined. The current thinking is that, if an inappropriate bias is included, the analysis rejects the radiance observations (near the surface), then the bias is never properly adjusted. To test this, an experiment started with zero bias is being started, this should spin up a new bias correction. Most of the system testing has simply carried bias corrections along from older systems.

So, while the system is getting closer and we are certainly learning more on the system with every experiment, the important validation experiments have not yet begun. Some minor corrections have also been identified. For example, it was found that snow was reaching the surface in regions too warm and equatorward. The snow production algorithm was not including surface temperatures, so now a check has been added.

The 2 degree experiment to test SSMI in the late eighties has progressed into 1987, and is closing on the onset of SSMI in July. However, the experiment is being removed from the priority queues. The GMAO is gearing up for operational support for TC4, which needs high priority, and also the experimentation on the sawtooth problem takes priority.

To emphasize the critical nature of the sawtooth problem, the figure below shows an example of how it looks at the worst. The time series is 850 mb temperature at a point every 6 hour analysis time. The points closest to the NCEP operational analysis are the when sondes are present (00Z and 12Z) and the very warm temperatures are when only satellite data are available. At this point, the GEOS5 surface temperature is much colder than NCEP and the surface channel radiances are being rejected by the quality controls.

June 11 Follow up: Recent experiments have shown that the AMSU channels over ice may be the root of the sawtooth problem. Further work is aimed at identifying specific channels. Result should be posted in the next status report, probably Friday June 15.