19th Conf. on weather Analysis and Forecasting/15th Conf. on Numerical Weather Prediction


Cloud/hydrometeor initialization in the 20-km RUC Using radar and GOES data

Dongsoo Kim, NOAA/FSL, Boulder, CO; and S. G. Benjamin and J. M. Brown

Toward the goal of improved short-range forecasts of cloud/hydrometeors, icing, and precipitation, an advanced version of the Rapid Update Cycle (RUC) cloud-hydrometeor assimilation technique with radar and GOES has been developed and tested. A version of this technique using GOES single field-of-view cloud-top pressure data provided by NESDIS, is being implemented into operations at the National Centers for Environmental Prediction (NCEP) along with a major upgrade to the RUC in April 2002. The new version of the RUC, called RUC20, also includes a change in horizontal resolution from 40 km to 20 km and significant changes to the analysis and model forecast components. The addition of GOES cloud-top assimilation to the RUC20 is shown to have a beneficial effect on cloud forecasts out to 12 h in duration.

Previous versions of the RUC technique for assimilation of GOES cloud-top pressure have been reported on by Kim and Benjamin (2001, 2000). In this paper, we present more recent modifications to the RUC cloud/hydrometeor analysis technique using GOES cloud-top data as well as initial experiments toward assimilation of radar reflectivity. Testing has started at FSL toward assimilation of radar reflectivity into the RUC to augment the assimilation of GOES cloud-top pressure data. Data sets examined include a real-time 2-km resolution reflectivity mosaic from WSI (Weather Services International) and a 10-km resolution Radar Coded Message (RCM) from NWS. Both are processed for each 20-km RUC gridpoint. While the WSI reflectivity data provide higher resolution, the RCM data provide beam blockage area information that helps to differentiate "no echo" from "no coverage".

Initial experiments with reflectivity data assimilation have been performed by adjusting the background (1-h forecast) mixing ratio profiles of rain water, ice, snow, and graupel, such that the maximum reflectivity (dBZ) of the column is close to the WSI maximum reflectivity. Examples of assimilation and forecast differences from radar and GOES assimilation will be presented at the conference.

extended abstract  Extended Abstract (252K)

Session 12, Data Assimilation II
Thursday, 15 August 2002, 1:30 PM-3:00 PM

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