Assimilation of T‐TREC‐retrieved wind data with WRF 3DVAR for the short‐term forecasting of typhoon Meranti (2010) near landfall

Abstract

AbstractAn extended Tracking Radar Echo by Correlation (TREC) technique, called T‐TREC technique, has been developed recently to retrieve horizontal circulations within tropical cyclones (TCs) from single Doppler radar reflectivity (Z) and radial velocity (Vr, when available) data. This study explores, for the first time, the assimilation of T‐TREC‐retrieved winds for a landfalling typhoon, Meranti (2010), into a convection‐resolving model, the WRF (Weather Research and Forecasting). The T‐TREC winds or the original Vr data from a single coastal Doppler radar are assimilated at the single time using the WRF three‐dimensional variational (3DVAR), at 8, 6, 4, and 2 h before the landfall of typhoon Meranti. In general, assimilating T‐TREC winds results in better structure and intensity analysis of Meranti than directly assimilating Vr data. The subsequent forecasts for the track, intensity, structure and precipitation are also better, although the differences becomes smaller as the Vr data coverage improves when the typhoon gets closer to the radar. The ability of the T‐TREC retrieval in capturing more accurate and complete vortex circulations in the inner‐core region of TC is believed to be the primary reason for its superior performance over direct assimilation of Vr data; for the latter, the data coverage is much smaller when the TC is far away and the cross‐beam wind component is difficult to analyze accurately with 3DVAR method.