Assimilation of Airborne Radar Radial Velocity Data with the GSI based EnKF-3DVAR Hybrid System for the Prediction of Hurricane Irene (2011)

The Gridpoint Statistical Interpolation (GSI) based hybrid ensemble Kalman filter (EnKF)-3D-Var system interfaced with the Hurricane Weather Research and Forecasting (HWRF) model, is used to assimilate the airborne radar radial velocity data for the prediction of Hurricane Irene (2011). In this hybrid system, flow-dependent ensemble covariance estimated from the EnKF is incorporated into the variational cost function using the extended control variable method. The data assimilation cycles were conducted during the flight missions, with the TDR radial velocity (Vr) data assimilated according to the flight legs. The Vr data are thinned after fore and aft sweeps are separated. Verification against independent in situ and remotely sensed observations shows that the analyses provided by the hybrid system capture the hurricane structure and intensity well. The 48-h forecast 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. Extensive testing and tuning of the hybrid system with more missions and cases are ongoing and the results will be presented in the conference.