10.2
Experiments of high-density data in the NCEP Eta Data Assimilation System: NEXRAD radial velocity and satellite radiance data
PAPER WITHDRAWN
Eric Rogers, NOAA/NWS/NCEP, Camp Springs, MD; and D. Parrish, M. Pondeca, Y. Lin, and G. DiMego
In the past 2 years NCEP has made significant enhancements to the operational Eta analysis and forecast system to provide higher-resolution mesoscale guidance, culminating with the implementation of the 12 km / 60 level Eta model in November 2001. With the high-resolution Eta Data Assimilation System (EDAS) in place, NCEP has begun experiments to assimilate high-density observational data sets using the Eta 3DVAR analysis. One source of high-resolution data are the radial wind velocities derived from the NEXRAD radar network. For use in the EDAS, the raw radar wind data is converted into a super observation with a spatial resolution of 5 km and 6 degrees of azimuth. To account for beam spread with distance from the radar, a new type of non-linear forward model has been defined for the radial winds. Winds at all Eta levels covered by the estimated vertical spread of the radar beam are adjusted so that the observation is as close as possible to the interval between the minimum and maximum wind at the selected levels. All winds, out to the maximum range of the radar (250 km), can be used by the new Eta 3DVAR forward model. If the EDAS data quality control algorithm rejects the Vertical Azimuth Display (VAD) winds for a given radar (e.g., due to contamination by migrating birds) the radial winds from that radar are not used. Results from EDAS experiments at 32 km and 12 km will be presented, along with future planned enhancements.
Although satellite radiance data from the GOES and polar-orbiting TOVS platforms have been used in the EDAS since September 2000, the data used has been significantly thinned (1/3rd of GOES data, 1/20th of TOVS HIRS data, 1/4th of TOVS AMSU-A and 1/48th of TOVS AMSU-B) so that the 3DVAR analysis would converge to a solution in a reasonable time. With greater computer power and more sophisticated algorithms, NCEP has begun experiments to assimilate higher-resolution radiance data. Results from EDAS experiments at both 32 km and 12 km resolution will be presented.
Session 10, Data Assimilation I
Thursday, 15 August 2002, 8:00 AM-9:58 AM
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