An analysis of spatial and temporal variations in the axisymmetric precipitation structure associated with typhoons making landfall on the southeastern coast of China based on the Doppler radar data

This study investigated temporal and spatial variations in the precipitation structure within 300 km radius from typhoon center by using the reflectivity data taken from the Doppler radars located in Wenzhou (CINRAD WSR98D) and Wufenshan, Taiwan, China. Six typhoons making landfall along the southeastern coast of China in the years of 2004-2007 have been selected to examine changes in the precipitation distribution from 18 h before landfall to 6 h after landfall. The axisymmetric component of typhoon rainfall, represented by the radial distribution of the azimuthally mean reflectivity, reveals that the maximum rainfall is located in the eyewall and a secondary maximum rainfall is in the rainband outside from 9 to 18 h before landfall. With increasing storm intensity, the maximum rainfall rate increases while its radius from the typhoon center decreases. When typhoons are approaching the coast, the mean rainfall rate in the innercore region increases abruptly, accompanied with the rapid contraction of the outring precipitation toward typhoon center. The highest intensification factor of the mean rain rate in the innercore of the six typhoons reaches 3.2. The peripheral rainbands contract to typhoon center simultaneously, and the rates of contraction decrease with typhoon intensifying. After typhoon landfall, the eye is filled by rain and the intensity decreases quickly with the precipitation shrinking continuously. As a result, the amount of rainfall in the innercore attenuates gradually. Finally, a model was proposed in this paper to fit the observed precipitation curve before typhoon landfall. This model is able to quantitatively describe the profile of the azimuthally mean rain of typhoon, and reveal the characteristic of twopeak of the profile. The maximum of the RMSE between the observed curve and the simulative result was 5.3 mm/h while the minimum was only 0.46 mm/h, suggesting that the model can well fit the real outline of typhoon precipitation.