Weather and Climate Systems

Assimilation of radar radial velocity data using hybrid systems for the prediction of Hurricanes Ike and Irene

Yongzuo Li
CAPS / OU School of Meteorology

26 February 2014, 3:00 PM

National Weather Center, Room 5600
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

In first part of the seminar, an enhanced version of the hybrid ensemble–three-dimensional variational data assimilation (3DVAR) system for the Weather Research and Forecasting Model (WRF) is applied to the assimilation of radial velocity (Vr) data from two coastal Weather Surveillance Radar-1988 Doppler (WSR-88D) radars for the prediction of Hurricane Ike (2008) before and during its landfall. In this hybrid system, flow-dependent ensemble covariance is incorporated into the variational cost function using the extended control variable method. The analysis ensemble is generated by updating each forecast ensemble member with perturbed radar observations using the hybrid scheme itself. The Vr data are assimilated every 30 min for 3 h immediately after Ike entered the coverage of the two coastal radars.Verification shows that hybrid method improves both analysis and free forecast.


In second part of the seminar, the unified Gridpoint Statistical Interpolation (GSI) based hybrid ensemble Kalman filter (EnKF)-three dimensional variational data assimilation (3DVAR) system interfaced with the Hurricane Weather Research and Forecasting (HWRF) model, is used to assimilate the airborne tail Doppler radar (TDR) radial velocity data for the prediction of Hurricane Irene (2011). In this hybrid system, flow-dependent ensemble covariance estimated from the ensemble Kalman filter (EnKF) is incorporated into the variational cost function using the extended control variable method. The analysis ensemble is generated by updating each forecast ensemble member with a serial implementation of the square root ensemble Kalman filter (EnSRF) system. The data assimilation cycles were conducted during the hurricane reconnaissance flight missions, with the TDR radial velocity (Vr) data assimilated according to the flight legs. The Vr data are thinned after fore and aft TDR sweeps are separated.

The subsequent 48-h deterministic forecasts initialized from the analysis of the hybrid system produces substantially smaller track and intensity errors than those such as operational HWRF forecast, forecasts without assimilating the TDR data and forecasts initialized by the analyses generated by the GSI 3DVAR with static covariance.

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