基于TRMM卫星资料揭示的长江流域梅雨季节降水日变化

利用1998~2013年热带测雨卫星TRMM 3B42降水率资料以及NCEP/CFSR温度场、气压场和风场等再分析格点资料等,从气候学角度揭示了长江流域梅雨季节降水和对流的日变化特征,探讨了典型和非典型梅雨锋年降水日变化差异,分析了大气环境场要素的日变化特征及其对降水和对流日变化影响。结果表明:(1)强降水在夜间发生在长江上游,白天发生在长江中下游。降水日变化特征显著,长江上游、盆地以东的中游以及中下游的沿江以南地区降水日峰值分别出现在午夜、清晨08时以及傍晚17时。沿江以北地区降水表现出半日循环,具有08时和17时两个峰值,午后峰值明显强于清晨。(2)长江中游地区降水日位相较上游地区延迟约6 h,下游地区日位相进一步向后推移,同时下游地区降水强度和范围明显强于上游,降水日较差也更明显。(3)典型梅雨锋年和近15年梅雨季节平均的降水日变化分布特征较为一致,非典型梅雨锋年较前两者日峰值出现时间明显提前。(4)短时强降水和深对流有较好的对应关系,白天高发区位于长江下游,夜间位于上游。(5)大气温压场在梅雨锋两侧显著的日变化差异使梅雨锋强度和结构在昼夜形成了差异,并使低层风场的辐合位置产生了日变化,这些大气环境场的日变化最终导致了梅雨期对流和降水的日变化。

ANALYSIS OF DIURNAL VARIATION OF MEIYU SEASON RAINFALL OVER THE YANGTZE RIVER BASIN BY TRMM SATELLITE DATA

Using the TRMM satellite precipitation data and NCEP/CFSR reanalysis data of temperature, high and wind filed from 1998 to 2013, the characteristics of diurnal variation of Meiyu season precipitation and convection over the Yangtze River Basin were revealed from the point of Climatology. The difference of diurnal variation of rainfall between typical and non-typical Meiyu years, the diurnal variation characteristics of atmospheric elements and their effects on the precipitation and convection were also analyzed. The results showed that, (1) the intense rainfall mainly occurred in the eastern Tibetan Plateau to the Sichuan basin during the night, in the middle and lower reaches of the Yangtze River during the day. The features of diurnal variation of precipitation were significant. The precipitation day peaks in the eastern Tibetan Plateau to the Sichuan basin, the middle reaches of the Yangtze River and Southern China respectively occurred on the middle night, 08 h early morning and 17 h late afternoon. The rainfall in the Yangtze-Huaihe river basin showed semidiurnal cycle, with the two peaks of 08 and 17 h, the afternoon peak was much stronger than the morning. (2) The daily rainfall in the middle reaches was delayed 6 h than the upper reaches of Yangtze River, the lower reaches was further backward, but the intensity and scope of precipitation was much stronger than the upper reaches. (3) The distribution of diurnal variation of typical Meiyu year is consistent to the nearly 15 years of Meiyu season average. The evolution form of non-typical was similar to the above two, only the daily peak time was ahead. (4) The short-time heavy rainfall had a good relationship to the deep convection. The high frequency area was happed in the lower reaches of Yangtze River (the eastern Tibetan Plateau to the Sichuan basin) during the day (night). (5) The diurnal variation of atmospheric temperature and pressure caused the intensity and structure differences of Meiyu front between the day and night. The lower troposphere wind speed was found to gradually weaken in the day, increase in the night, and produced diurnal variation of position of convergence at low level wind filed. These resulted in the diurnal variation of the rainfall and convection of Meiyu season.