北半球夏季海洋性大陆区域降水与南方涛动联系的年代际变化

利用1960—2016年夏季美国国家海洋和大气管理局(NOAA)的月平均降水资料、南方涛动指数SOI以及Niňo3指数资料、NCEP/NCAR再分析资料以及英国哈德莱中心海表温度资料,通过相关分析和回归分析,研究了北半球夏季海洋性大陆区域(Maritime Continent,MC)降水与ENSO联系的年代际变化特征。结果表明:MC地区夏季平均降水与SOI指数的相关自1998年后明显减弱。造成这种现象的原因是:南方涛动指数SOI与海温相关系数在太平洋中部为负的大值中心,且1998年之后海温异常呈中部型。这种SSTA强迫造成1998年后大气视热源异常亦偏于赤道太平洋中部,这有利于通过Gill型响应,使菲律宾以东的对流层低层存在明显的反气旋性环流,辐散增强,从而造成赤道以北降水显著减少,抵消了MC区域内南部地区降水的增加,破坏了原有的SOI为正(负)时MC地区平均降水异常增加(减少)的关系。

Interdecadal changes in the relationship between summer oceanic continental precipitation and southern oscillation in Northern Hemisphere

By using the NOAA precipitation data, the Southern Oscillation Index(SOI) and Niño3 index, the monthly mean data from NCEP/NCAR Reanalysis, the monthly mean sea surface temperature data from Hadley Center over the period of 1960-2016, we have investigated the interdecadal variation characteristics of relationship between summer precipitation and ENSO in the Maritime Continent(MC) region of the northern hemisphere through correlation analysis and regression analysis. When SOI is positive(negative), precipitation anomaly over MC is positive(negative), too. Results show that the correlation between SOI and summer precipitation over MC area has significantly weakened since 1998. The reason for this phenomenon is that the correlation of SOI and Sea Surface Temperature(SST) is negative in the central Pacific. The negative correlation center has shifted eastward and manifested as CP-type SSTA after 1998. This type of SSTA corresponds to the center of apparent heat source anomalies located in the central Pacific, which induces the Gill-type response of atmosphere, leading to an anomalous anticyclonic circulation in the lower troposphere east of the Philippines, thus strengthening the divergence there. This causes the precipitation over area north of equator to significantly decrease, canceling the precipitation increase over southern part of the MC, making the relationship between the precipitation and SOI loose.