Comparison of Cloud/Rain Band Structures Between High-Resolution Numerical Simulation of Typhoon Lekima (2019) and FY-4A Advanced Geostationary Radiation Imager Observations

Abstract

Higher cloud top and stronger convection within Typhoon Lekima (2019) corresponds to lower brightness temperature (TB) from Fengyun-4A (FY-4A) Advanced Geostationary Radiation Imager (AGRI) observations. In this study, an effort is made to see if all-sky TB simulations from short-term model forecasts by a radiative transfer model could capture observed low-TB distributions. We employ a coupled ocean-atmosphere Weather Research and Forecasting (WRF) model at 3-km resolution and the European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis v5 (ERA5) and the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) analysis as initial conditions. Horizontal structural distributions of all-sky TB simulations initialized by the NCEP GFS analysis better match AGRI observations than the ERA5 reanalysis, including the eyewall, moat and spiral rainband distributions of Typhoon Lekima. The cloud top pressure in most cloud areas near the center of Lekima is around 140 hPa, whereas in some rainbands far from the center is approximately 700 hPa. A high correlation in horizontal distributions of all-sky TB simulations with relative vorticity fields during the 24-hr period of WRF model forecasts suggests a potential relationship between dynamic and thermodynamic variables. The farther from the center of Lekima, the greater the proportion of high-wavenumber structures within both TB and relative vorticity fields. Within the radius of maximum wind speed, the azimuthal wavenumbers 0, 1, and 2 shown in TB and relative vorticity fields have greater comparability. High wavenumber structures in relative vorticity increase with radial distance in a way faster than those in TB.