9B.5 The Impact of Assimilating Surface Pressure Tendency Observations on Severe Weather Events in a WRF Mesoscale Ensemble System

Tuesday, 28 October 2008: 5:30 PM
South Ballroom (Hilton DeSoto)
Dustan M. Wheatley, NOAA/NSSL, Norman, OK ; and D. J. Stensrud

Surface pressure observations provide significant information on the properties of mesoscale features, such as cold pools, that affect convective development. While a number of studies have demonstrated the potential benefits of assimilating total surface pressure fields, little effort has been given to assimilating surface pressure tendency fields, which at times depict more coherent mesoscale structure than total surface pressure fields. To explore the impact of this dataset, routine hourly surface observations of temperature, winds and pressure tendency are assimilated into a 30-member Weather and Research Forecasting (WRF) mesoscale ensemble that accounts for initial condition and model physics uncertainties. The ensemble Kalman filter (EnKF) approach encoded in the Data Assimilation Research Testbed (DART) framework is employed in this study. Hourly analyses are generated for the period 1300 UTC to 0600 UTC on a continental United States domain with a horizontal gridpoint spacing of 30 km. Preliminary work has focused on the analyses and forecasts of derecho-producing convective systems from 4-5 July 2003 over Indiana and 19-20 June 2007 over Texas.

The benefit of assimilating pressure tendency data is evaluated through comparison to an ensemble that assimilates only surface temperature and wind data. The relative performance of the original EnKF experiment is also compared against an ensemble that assimilates altimeter setting. In both comparisons, the primary objective is to establish a method for assimilating surface pressure data that produces the best analyses of mesoscale features, such as cold pools, and attendant circulations in the ensemble mean fields. Impacts of the pressure assimilation on severe weather parameters will be discussed and implications examined.

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