Asymmetries of Tropical Cyclone Convection in Different Intensity Change Stages as Derived from Satellite 85 and 37 GHz observations

The asymmetries of convection in tropical cyclones (TCs) are of particular interest for TC intensity change forecasts, especially for rapid intensification (RI). In this study, the climatology of convection asymmetries relative to the environmental wind shear in different storm intensity changes is investigated. The main tool used for this work is a 14-year Tropical Rainfall Measuring Mission (TRMM) Tropical Cyclone Precipitation Feature (TCPF) database that contains 1146 TCs viewed by TRMM during 1998 and 2011. The TRMM TCPF database contains global TC best track information, TRMM radar and passive microwave observations, and environmental parameters from the ECMWF interim reanalysis. A subset of 2955 manually re-centered TC overpasses well-observed by the TRMM Microwave Imager (TMI) will be used in this research. To be included in the study, the TMI overpass must cover at least 200-km radius from the TC center. The dataset is divided by future 24-hour intensity change and exclusively includes storms with at least moderately favorable environmental conditions. The Fourier wavenumber analysis is applied to all the qualified TMI TC overpasses to calculate the first-order (wavenumber-1) asymmetries of 85 and 37 GHz Polarization Corrected brightness Temperature (PCTs), 37 GHz horizontally polarized brightness temperature (37H) and 37 GHz vertically polarized brightness temperature (37V). The TCs in each intensity change category are combined into composite diagrams orientated relative to the environmental vertical wind shear direction. The distribution and amplitude of asymmetry of these convective parameters will be compared for different intensity change stages and different TC-prone basins. The 85 and 37 GHz PCTs are associated with ice-scattering signature above the freezing level, while the 37H and 37V are associated with lower-level precipitation. The maximum wavenumber-1 phase differences between these upper-level and lower-level convection/precipitation parameters will be examined to evaluate the asymmetry characteristics in different levels for different storm intensity change stages. The results will show whether the degree of symmetry of convection quantified by different parameters is a good indicator of TC intensification and especially RI, and also show the convection structure differences between different TCs intensity change stages.