冬季北太平洋大气低频环流的年际和年代际变化特征及其与大气环流和海温异常的联系

利用1979—2015年ECMWF逐日再分析资料,通过EOF分解和回归分析研究了冬季北太平洋大气低频环流的年际和年代际变化特征及其与海表面温度异常(SSTA)和大气环流异常之间的联系。研究结果表明:冬季中纬度北太平洋地区850 h Pa低频尺度环流存在3个明显的变化模态:第一模态为海盆尺度的单极型异常气旋(反气旋)式环流,同期太平洋SSTA呈现El Ni1o(La Ni1a)以及PDO暖位相(冷位相)空间分布,阿留申低压强度增强(减弱),对流层中高层是正位相(负位相)的PNA型遥相关,北太平洋天气尺度风暴轴中东部南压(北抬);第二模态为在白令海峡和副热带地区呈气旋式与反气旋式环流南北向偶极型变化,同时中纬度北太平洋SSTA呈现NPGO(North Pacific Gyre Oscillation)正位相(负位相)的空间分布,黑潮区域SSTA偏暖(偏冷),北太平洋SSTA经向梯度加大(减小),对流层中高层为负位相(正位相)的WP型遥相关,北太平洋天气尺度风暴轴整体偏北(偏南),强度增强(减弱);第三模态为北太平洋中西部和北美西岸呈气旋式与反气旋式环流东西向偶极型异常,黑潮区域SSTA偏冷(偏暖)而北太平洋东部SSTA偏暖(偏冷),SSTA纬向梯度加大(减弱),同时赤道东太平洋出现类似La Ni1a(El Ni1o)的SSTA分布,北太平洋天气尺度风暴轴中东部明显减弱(加强)而西部略有加强(减弱)。

Interannual and interdecadal variations of atmospheric low-frequency circulation over the North Pacific in winter and its relationship with the atmospheric circulation and SST anomaly

The daily reanalysis data of ECMWF from 1979 to 2015 are used in Empirical Orthogonal Function (EOF) analysis and regression method to investigate the interannual and interdecadal variations of atmospheric low-frequency circulation over the North Pacific in winter and its relationship with the Sea Surface Temperature Anomaly (SSTA) and midlatitude atmospheric circulation anomaly.The results show that there are three main variation modes of the 850 hPa low-frequency scale circulation over the midlatitude North Pacific in winter.The first mode depicts the one pole abnormal cyclonic (anticyclone) circulation of basinwide scale.Meanwhile,the SSTA presents El Niño (La Niña) pattern and PDO is in warm phase. The intensity of the Aleutian Low increases (decreases) and the middle and high troposphere is of positive (negative) phase of PNA.The mid-east part of the synoptic scale storm track moves southward (northward) in North Pacific. The second mode depicts a meridional dipole pattern with a cyclone in Bering Strait and an anticyclone in the subtropical areas.Meanwhile,the SSTA is of positive (negative) phase of NPGO over the midlatitude North Pacific. SSTA in the Kuroshio Current is warmer (colder) than usual and the meridional SSTA gradient increases (decreases).The middle and high troposphere is of negative (positive) phase of WP. The synoptic scale storm track moves northward (southward) with its intensity increases (decreases) in North Pacific. The third mode depicts a zonal dipole pattern with a cyclone in the central North Pacific and an anticyclone in the west coast of North America.Meanwhile,SSTA in the Kuroshio Current is colder (warmer) but in the eastern North Pacific,it is warmer (colder) than usual. The zonal SSTA gradient increases (decreases) and it is similar that SSTA is of La Niña (El Niño) pattern in the equatorial eastern Pacific. The mid-east part of the synoptic scale storm track weakens (strengthens) obviously but the west part of it strengthens (weakens) slightly.