Observed Axisymmetric and Asymmetric Rainfall Structure in Landfalling Tropical Cyclones of China

In this study, axisymmetric and asymmetric rainfall structure evolutions in tropical cyclones (TCs) that made landfall in China from 2001 to 2009 were analyzed based on the TRMM satellite 3B42 rainfall estimates. The results revealed that in landfalling TCs, the wavenumber-zero rainfall was closely related with the TC intensity. The wavenumber-zero rainfall was decreased generally with the decreasing TC intensity during landfall. The TCs of higher (lower) intensity had higher (lower) peak axisymmetric rain rates, with higher (lower) amplitudes of wavenumber-zero rainfall component relative to the total rain and lower (higher) wavenumber-1, 2, 3, 4 rainfall components relative to the total rain. The axisymmetric rainfall was also related with the TC intensity change. It is found that for the TCs of larger intensity change rate, they had the same larger rain change rate. According to the TC intensity change rate, the landfalling TCs were categorized to five groups, including rapid decay (RD), slow decay (SD), unchanged, slow intensification (SI), and rapid intensification (RI). The TCs of RD (RI) had the lowest (highest) peak averaged rain rate and the largest (smallest) averaged radius of the peak rain. For TC rainfall asymmetries relative to the coastlines, the landfalling TCs rainfall maximums were generally in the offshore side, and in the downshear to downshear-left. The TC intensity and motion speed seemed to have no obvious impacts on the rainfall maximum location during landfall. But when the shear was turned smaller, the asymmetric rainfall maximum locations would be changed from the downshear and offshore side to the upshear and onshore side at the time of landfall, which indicated that the coastline could have obvious effects on the rainfall asymmetry during landfall when the environmental vertical wind shear was weak. Key words: Tropical cyclones, Structure, Rainfall, Landfall