关键词: 华南, 台风, 降水日变化, 台风登陆前, 外围环境场

Abstract:

We used the Japan Meteorological Agency (JMA) best track data, tropical rainfall measuring mission (TRMM) 3B42 3-hourly precipitation data and Japanese 55-year reanalysis (JRA-55) 6-hourly data from 1998 to 2017. We selected typhoons, which originated from the Northwest Pacific and had rain belt passing through South China with moving path located to the south of Taiwan Island, as our research objects. The date of the first spiral rain belt of typhoon arriving in South China was manually judged from satellite cloud images and TRMM precipitation data. The influences of typhoons on diurnal variation of precipitation in the study area before the rain belt arriving were then analyzed. The results showed that on the one hand the peripheral circulations of typhoons would transport much water vapor into the region before typhoon landfall, which was beneficial to the precipitation in the region; on the other hand, the downdraft outside of cyclonic divergence field would suppress the convection in the region, which was inconducive to the occurrence of precipitation. When the former played a greater role than the latter, the precipitation in South China would increase. The maximum of atmospheric instability within a day would occur in the afternoon, resulting in an afternoon rainfall peak. These relevant typhoons appeared mostly in July and August, when the western Pacific subtropical high was located easterly and was favorable for the northward movement of typhoon. The typhoon centers were close to the coastal area of South China when their first wave of rainband reached South China. On the contrary, the atmospheric layer over South China was stable and therefore precipitation decreased; the diurnal variation of precipitation peaked in the morning due to radiative cooling and the relevant typhoons mostly appeared in September and October. As the westward extension of the western Pacific subtropical high is not conducive to the northward movement of typhoon, the typhoon centers were far away from the coastal area of South China when their first wave of rain band reached South China. The results are expected to improve the knowledge for impact of cyclonic peripheral circulation on precipitation process in coastal regions before typhoon landfall.

Key words: South China, typhoon, diurnal variation of precipitation, before typhoon landfall, cyclonic peripheral circulation