近60年索马里急流越赤道水汽输送的变化特征及对中国初夏降水的影响

利用近60年(1951-2010年)的NCEP/NCAR再分析风、比湿、地面气压及降水资料,建立了一个越赤道水汽输送强度指数来表征索马里急流的强度,并从季节、年际、年代际变化及突变等不同侧面出发,比较系统地分析了索马里急流越赤道水汽输送强度的变化特征,并进一步分析了它与我国初夏降水异常的关系及这种关系随时间的年代际变化特点.分析结果表明:进入20世纪90年代之后,索马里急流风速强度有明显的减弱趋势,而水汽输送强度无显著变化;与索马里急流风速强度相比,水汽输送强度与我国初夏6月降水量的关系更为密切.索马里急流弱年对应长江以北的华北地区初夏降水偏少,反之亦然.此外,索马里水汽输送对我国北方初夏降水的影响在1982年后明显加强.

Variation of the Cross Equatorial Moisture Transport in Somali and Its Impact on China Early Summer Rainfall in Nearly 60 Years

Based on the NCEP / NCAR wind field, specific humidity, surface pressure and precipitation reanalysis data from 1951 to 2010, a cross equatorial moisture transport intensity index is established to characterize the strength of the Somali jet (SMJ), and the seasonal, interannual, decadal variations and mutations of the SMJ cross equatorial moisture transport intensity are studied, while comparing with the traditional SMJ wind speed intensity index. In addition, the relationship between SMJ and the China early summer precipitation is analyzed. Based on the above analysis, the decadal changes of this relationship are revealed. Main results are as follows. After the 1990s, the SMJ wind speed intensity index is weakening, but the SMJ water vapor transport has no significant variations; compared with the SMJ wind speed strength, the SMJ water vapor transmission intensity is associated with the China early summer rainfall more closely. When the SMJ is weaker, rainfall decreased in the Huanghe Huaihe River Basin and North China in early summer, and vice versa. Besides, this correlation has been strengthened in recent 30 years.