Wednesday, 12 February 2003
Operational Use of QuikSCAT winds in NCEP GDAS
QuikSCAT wind data of one degree longitude-latitude superobs were implemented in the Global Data Assimilation Systems (GDAS) of the National Centers for Environmental Prediction (NCEP) in January 15, 2002. This paper discusses results of a pre-implementation test, and those of a more recent experiment using QuikSCAT winds in NCEP numerical weather prediction operations. In the pre-implementation test with NCEP's operational resolution (75km horizontally) data assimilation system, a parallel global data assimilation experiment was conducted for a 45 days, starting on the 00 UTC cycle of September 27, 2001, and ending on the 00 UTC cycle of November 10, 2001. Based on time-series and average scores of 1000 mb and 500 mb anomaly correlations, and those of tropical wind RMS errors at 850 mb and 200 mb, from a total of 40 forecasts of this parallel experiment, NCEP obtained a positive impact of QuikSCAT wind data from day 1 up to day 5 forecasts. The impact is mostly seen in the low level ocean surface 10 meter wind and sea level pressure forecasts.
Recently, a parallel data assimilation experiment was conducted for a one month period using a half-degree longitude-latitude superobed resolution of QuikSCAT wind data in the NCEP operational GDAS. NCEP is implementing a new higher resolution GDAS with a forecast model of about 50 km horizontal resolution this summer, and the new GDAS should be capable of using "meso-scale" features contained in the half-degree superobed resolution of QuikSCAT wind data. The assimilation experiment was initiated on June 12, 00 UTC cycle 2002, and ended on 12 July 00 UTC cycle, 2002. Preliminary results of this experiment show that use of a half-degree superobed resolution of QuikSCAT winds leads to a small improvement in both Northern and Southern Hemisphere geopotential height forecasts, but a very large improvement in the tropics wind forecasts, when compared to results from the use of currently operational one-degree superobed resolution of QuikSCAT winds in the NCEP's GDAS.