冬季各月北太平洋涛动的年际变化及其与我国降水异常的联系

利用ERA-Interim的海平面气压(Sea Level Pressure,SLP)再分析资料和中国160站的降水观测资料,分析了冬季各月(当年12月、次年1月和2月)北太平洋涛动(North Pacific Oscillation,NPO)的年际变化特征,及其与我国同期降水异常之间的联系。结果表明:1)冬季各月NPO指数的年际变化较为显著,但各月NPO指数年际变化之间的相关性较差,1979—2012年冬季12月与1月NPO指数年际变化之间的相关系数为0.09,而1月与2月NPO指数的相关系数仅为-0.003,均没有通过信度检验。2)1月和12月NPO指数年际变化与同期我国黄淮流域降水异常之间存在明显的正相关,而2月NPO指数年际变化与同期我国华北降水异常之间为明显的负相关。3)当1月(12月)NPO指数增加1个标准差时,我国黄淮流域降水量比多年平均值增加约50%(40%);而当2月NPO指数增加1个标准差时,我国华北降水量比多年平均值减少约30%。

Interannual variation of the winter monthly North Pacific Oscillation and its association with precipitation in China

The North Pacific Oscillation(NPO) is one of the most prominent large-scale patterns of atmospheric low-frequency variability in the northern extratropics.It plays an important role in modulating atmospheric circulation and climate over the East Asian region.Based on the ERA-Interim sea level pressure data,along with the observed precipitation data of 160 stations in China provided by the National Climate Center,spanning from January 1979 to December 2013,the interannual variation of the winter monthly(December,January and February) NPO and its association with simultaneous precipitation in China and atmospheric circulation over East Asia are investigated in this paper through use of correlation analysis,linear regression analysis and Morlet wavelet analysis.The results show that the monthly NPO has a significant interannual variation in wintertime.The index of the monthly NPO has a 2-4 yr period.Importantly,however,the correlations among the interannual variation of the winter monthly NPO indices are weak.During 1979-2012,the correlation coefficients between the NPO index in December and that in January is 0.09,while between January and February it is only -0.003,without passing the reliability test at the 95% confidence level.Additionally,it is shown that the interannual variation of the NPO impacts evidently upon the precipitation anomalies over East China.Significant positive correlation is found between the interannual variations of the NPO and the precipitation over the Huanghuai River valleys in December and January.However,the interannual variation of the NPO in February relates negatively to the precipitation over North China in February.The precipitation over the Huanghuai River valleys increases by about 50%(40%) compared with its climatology as the NPO index increases by one standard deviation in January(December).Meanwhile,when the NPO index increases by one standard deviation in February,the precipitation over North China decreases by about 30%.Furthermore,the monthly NPO is closely associated with anomalous East Asian atmospheric circulation,which leads to anomalous precipitation over East China.When the NPO index is positive in December and January,the simultaneous sea level pressure and 500 hPa geopotential height anomalies are positive over East Asia.As a result,the precipitation over the Huanghuai River valleys increases in December and January.When the NPO index is negative in December and January,the simultaneous sea level pressure and 500 hPa geopotential height anomalies are negative over East Asia.Accordingly,the precipitation over the Huanghuai River valleys decreases in December and January.When the NPO index is positive in February,the sea level pressure anomalies are positive over northwestern China and Inner Mongolia and the 500 hPa geopotential height anomalies are negative over northeastern China,which leads to a decrease in precipitation over North China in February.Lastly,when the NPO index is negative in February,the sea level pressure anomalies are negative over northwestern China and Inner Mongolia and the 500 hPa geopotential height anomalies are positive over northeastern China,resulting in increased precipitation over North China in February.