9B.3
Radar Reflectivity Assimilation for the Hourly RUC and Rapid Refresh
Stephen S. Weygandt, NOAA / ESRL / GSD, Boulder, CO; and S. G. Benjamin and J. M. Brown
We have developed an effective procedure for assimilation of radar reflectivity as available over the CONUS from NCEP's version of NSSL's Q2 reflectivity mosaic. At the Global Systems Division of the NOAA Earth System Research Lab, this is being applied in both the developmental Rapid Update Cycle (RUC) and its replacement currently under development, the Rapid Refresh (RR).
The procedure identifies volumes of the atmosphere where we have confidence there are precipitating hydrometeors based on evidence from radar, satellite and METAR surface observations. We then construct a temperature tendency field based on an estimated rate of latent heat release needed to produce these hydrometeors, and insert this temperature tendency into the forward (diabatic) portion of the Digital Filter Initialization. (In model grid columns where we have no clear indication that hydrometeors exist, we use the temperature tendencies produced by the physics parameterizations without modification). Using this combined tendency field in the forward (diabatic) portion of the DFI procedure produces a divergent wind component that has a measure of dynamical consistency with the observed reflectivity. The model forecast thus starts with a vertical motion field that allows initial precipitating systems to have time continuity into the forecast. The result is much improved precipitation during the first few hours of the forecast. This assimilation technique will be part of the NCEP operational RUC in its fall 2008 change package, and will become part of the initial implementation of the 13-km RR, to replace the RUC in 2010.
In this presentation we demonstrate, through the use of case studies, the advantages of combining high resolution and rapid updating for very short range (3-12h) forecasting of convection. The importance of the initialization procedure, and the challenges it presents, will be discussed.
A companion paper by Smith et al. at this conference will show application of this radar reflectivity assimilation from the RUC and Rapid Refresh to initialize an hourly 3-km grid spacing, explicit convection WRF-based model called the High Resolution Rapid Refresh (HRRR).
Recorded presentationSession 9B, Data Assimilation
Tuesday, 28 October 2008, 4:30 PM-6:00 PM, South Ballroom
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