Extended Abstract (2.0M)6.2
Implementation of the radar-enhanced RUC
Stan Benjamin, NOAA/ESRL, Boulder, CO; and S. Weygandt, J. M. Brown, T. Smirnova, D. Devenyi, K. Brundage, G. Grell, S. Peckham, T. W. Schlatter, T. L. Smith, and G. S. Manikin
In this report, we describe changes and testing for a significant RUC upgrade at NCEP planned for January 2008, about the time of this conference. These changes will have important modifications to aviation guidance using RUC grids, primarily for improvements in short-range convection forecasts, winter storm forecasts, and surface forecasts.
The most important part of the RUC change package is assimilation of 3-d radar reflectivity primarily by specification of 3-d radar-based latent heating during a pre-forecast diabatic digital filter initialization (DFI). This change has been in testing at NOAA/ESRL/GSD in real-time RUC cycles since February 2007. A number of revisions have been developed during this initial testing period, including more careful QC procedures for the radar reflectivity data, and in the specification of latent heating. A convection suppression technique has also been developed as part of the RUC radar assimilation to suppress erroneous convection in the RUC background forecast in echo-free regions. A secondary contribution of the RUC radar reflectivity assimilation is to complement satellite cloud-top and METAR ceiling/visibility so as to modify the background 1-h RUC 3-d hydrometeor/water vapor forecast. Proxy reflectivity, calculated using lightning stroke density, supplements the radar reflectivity data in areas of no radar coverage.
The experimental RUC model with radar assimilation has shown consistent improvement in reflectivity and precipitation forecasts out to 6h, with smaller changes still evident often in 12h forecasts. This retention is achieved by changes to the 3-d divergent wind field via the assimilation technique. Some of the improvement is also attributable to changes in the Grell-Devenyi convective parameterization used in the RUC model.
All of the RUC upgrade changes below will be described briefly at the conference presentation:
· Assimilate radar reflectivity – components in both analysis and model. Builds convection where needed and suppresses erroneous convection.
· Assimilate mesonet winds from accepted provider uselist
· Change of longwave radiation scheme from current Dudhia (1989) to Rapid Radiative Transfer Model (RRTM – Mlawer et al 1997) – primary effect - less warm bias in warm season
· Modification to Grell-Devenyi convective scheme to reduce excessive areal coverage for light precipitation and to improve coherence of areas of thunderstorms.
· Modification to snow component of RUC land-surface model (Smirnova et al. 2000) for snow density to decrease the incidence of excessively low 2-m air temperatures over fresh snow cover at night
· Add reflectivity products similar to those for the NCEP North American Mesoscale (NAM) model).
Session 6, Nowcasting and Modeling Part II
Tuesday, 22 January 2008, 11:00 AM-12:00 PM, 226-227
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