Direct assimilation of simulated radar reflectivity for typhoon In-fa using EnKF: Issue with state variables updating

Abstract

Using a convective scale WRF-GSI system and a reflectivity observation operator based on the double-moment microphysics (Thompson) scheme, simulated radar reflectivity data are produced and then directly assimilated with EnKF through Observing System Simulation Experiments (OSSEs) for the case of typhoon In-Fa (2021). We examined the ability of the EnKF to simultaneously estimate state variables and conducted sensitivity tests to evaluate the impact of updating different state variables. The results show that updating a full set of analysis variables can help obtain highly precise initial fields in the model and improve typhoon forecast skills. Excluding the horizontal wind update will affect the adjustment of the temperature field and the sea level pressure field during the cyclic assimilation process. Updating the variables directly related to the reflectivity operator alone could adjust hydrometers well, but the positive impact arising from the assimilation quickly vanishes during the forecast. In addition, this study also includes a quantitative RMSE analysis for each variable during the assimilation cycle and compares the effect of each schemes on different variables.

Keywords

• Radar reflectivity data
• EnKF
• Direct assimilation
• State variables