夏半年热带太平洋中部型海温异常与热带印度洋海盆模对同期中国东部降水的共同影响

Combined influences of tropical central Pacific SSTA and tropical Indian Ocean Basin Mode on precipitation in eastern China during summer half-year

摘要:

利用1961-2013年NCEP/NCAR再分析资料和HadISST月平均海表面温度资料，分析了夏半年热带太平洋中部型海温异常与热带印度洋海盆模（Indian Ocean Basin Mode，IOBM）的特征，并研究了不同位相配置时二者对同期中国东部气候的共同影响。结果表明：1）太平洋中部型海温异常指数与印度洋海盆模指数几乎相互独立。太平洋中部型海温异常与IOBM同位相变化（记为PPNN事件）和反位相变化（记为PNNP事件）时，热带印太地区海温异常分别呈三级型和偶极型分布。2）不同位相配置对中国东部地区降水异常的影响及其影响机制存在显著差异：当发生PPNN事件时，水汽从海洋性大陆（Maritime Continent，MC）地区向江淮流域输送；热带海温异常引起大气产生Gill型响应，维持了中国东部的环流异常；MC地区通过经向三圈异常垂直环流引起江淮流域降水异常增多。发生PNNP事件时，Gill型环流响应中心西移，长江流域降水偏少，水汽辐散；同时MC地区对流层低层准定常Rossby波能传播也有利于长江流域扰动的维持。这些结果对深刻认识中国东部地区夏半年降水异常成因和印度洋/太平洋海温异常不同分布的作用具有重要意义。

Abstract:

Based on the NCEP/NCAR reanalysis data and the HadISST monthly mean sea surface temperature(SST) data from 1961 to 2013,this paper investigates the characteristics of tropical central Pacific SST anomaly(SSTA) and tropical Indian Ocean Basin Mode(IOBM),and their combined influences on climate in eastern China during summer half-year.Results demonstrate that the tropical central Pacific SSTA pattern index(CPI) and IOBM index(IOBMI) are almost independent of each other in sense of statistics.When the CPI and IOBMI have same signs(referred to PPNN cases) and opposite signs(referred to PNNP cases),the tri-pole and dipole SSTA patterns are observed in tropical India Ocean and Pacific Ocean,respectively.Mechanisms behind different anomalous rainfall patterns in eastern China are different in PPNN and PNNP cases.In PPNN cases,moisture can be transported from Maritime Continent(MC) to the Yangtze-Huaihe River basin.The anomalous circulations in eastern China are generated and maintained due to Gill response of atmosphere to the tropical SSTA.The anomalous vertical circulation cells over region from MC northward to the Yangtze-Huaihe River show some connections between anomalous thermal forcing over MC and rainfall anomalies over the Yangtze-Huaihe River basin.However,in PNNP cases,no moisture is transported into the Yangtze River.Due to the significant westward shift of location of SSTA center in Pacific,the corresponding anomalous circulations also shift westward as a Gill response of atmosphere to central Pacific SSTA pattern.Meanwhile,Rossby wave energy can propagate into region south of the Yangtze River from MC,facilitating the maintenance of anomalous anti-cyclonic circulation over region south of the Yangtze River.These results are beneficial to us for better understanding the causes of rainfall anomalies and the role of SSTA patterns over Indo-Pacific region in inducing precipitation anomalies in eastern China.