北太平洋秋季海表温度异常影响冬季大气环流的主模态及其热动力特征*

The main mode of winter atmospheric circulation affected by sea surface temperature anomalies in the North Pacific during autumn and its thermal and dynamic characteristics

中文关键词:  北太平洋海表温度异常，非绝热加热，瞬变活动强迫，大气环流异常，主模态

英文关键词:Sea  surface temperature  anomaly in  the North  Pacifi, Diabatic  Heating, Transient  activity forcing, Atmospheric  circulation anomaly, Main  mode

中文摘要:

      [目的]为探讨北太平洋海表面温度对于中国极端天气的影响,[资料和方法]基于1977～2023年逐日和逐月NCEP/NCAR再分析资料,在去除ENSO影响下,运用最大斜方差 (Maximum covariance analysis,MCA)、回归和相关分析,采取海气耦合和天气瞬变涡动相结合的热、动力诊断方法,研究了北太平洋海表面温度异常(Surface sea temperature anomaly ,SSTA)对于大气环流异常的作用及可能机制,[结果]结果指出：初秋(ASO)北太平洋SSTA显著影响初冬(OND)大气环流(相应的空间分布型为主模态),主模态初秋(ASO)北太平洋SSTA具有明显的“西负东正偶极子”型分布特征,相应初冬(OND)大气环流异常呈“类PNA模态”分布,正、负异常环流中心相比SSTA中心偏北、偏东,其垂直分布为相当正压结构。[结论] 秋冬季北太平洋海洋-大气之间的相互作用通过非绝热加热和瞬变强迫相互耦合,晚夏“东西偶极子”型大气环流异常波列加深低空阿留申低压,冷(暖)平流加强,释放(获得)湍流热通量和非绝热加热(冷却),相应初秋“东西偶极子”SSTA加强,负SSTA南部海面锋区加强,大气低层斜压活动增强,高空瞬变活动加强；非绝热加热异常随季节向上传输并产生斜压反应,瞬变活动强迫在高空急流以北(南)产生负(正)变高(反)气旋式环流,高空较强。高空瞬变活动强迫随季节增强并向南移动,在其和非绝热加热异常共同作用下,从初秋(ASO)到初冬(OND),大气环流异常波列由“东西偶极子”转变为“类PNA模态”分布,上下结构和强度上分别经历“相当正压-弱斜压-相当正压”和“强-略有减弱-明显加强” 的转变过程；反之,大气环流异常强迫SSTA由“东西偶极子”转变为“马蹄型”分布,强度上经历了“强-减弱-减弱” 的转变过程。初秋(ASO)北太平洋SSTA通过持续性作用和瞬变活动强迫致使初冬(OND)大气环流异常明显增幅并实现统计上的显著性。初冬(OND)“类PNA模态”相应的北半球大气环流异常为一向下游传播到北美的显著性波列,对冬季大气内在变率PNA模态的形成具有一定的贡献,当初冬(OND)大气环流异常与冬季PNA模态同(反)位相时,PNA模态加强(减弱),PNA模态的强弱变化对中国极端天气的预测具有较强的指示意义。

英文摘要:

      To explore the impact of sea surface temperature in North Pacific on extreme weather in China, based on daily and monthly NCEP/NCAR reanalysis data from 1977 to 2023, through Maximum Covariance Analysis (MCA), regression, and correlation analysis after removing the influence of ENSO,the thermal and dynamic diagnostic method combining ocean-atmosphere coupling and weather transient eddies were adopted to study the role and possible mechanism of surface sea temperature anomaly (SSTA) in North Pacific affecting atmospheric circulation anomalies. The results indicate that the early autumn (ASO) North Pacific SSTA significantly affects the early winter (OND) atmospheric circulation (with the corresponding spatial distribution pattern as the main mode), the main mode of early autumn (ASO) North Pacific SSTA has a clear "west negative east positive dipole" distribution characteristic, and the corresponding early winter (OND) atmospheric circulation anomaly shows a "PNA like" distribution;the positive and negative abnormal circulation centers are northward and eastward compared to the SST anomaly center, and their vertical distribution is a fairly positive pressure structure. The interaction between the ocean-atmosphere in the North Pacific during autumn and winter is coupled through diabatic heating and transient forcing; in late summer, the anomalous wave train of the "East West Dipole" type atmospheric circulation deepens the low-level Aleutian low pressure circulation, strengthens the cold (warm) advection, and releases (obtains) turbulent heat flux and diabatic heating (cooling);correspondingly,the "East West Dipole" SSTA in early autumn strengthened, the southern sea front of negative SSTA area strengthened, the atmospheric low-level oblique pressure activity increased, and the upper transient activity increased; diabatic heating anomalies are transmitted upwards with the seasons and generate oblique pressure reactions,transient activity forces the formation of negative (positive) changes of high and (anti) cyclonic circulation to the north (south) of the upper level jet stream, with stronger upper levels. The upper transient activity forcing increase with the seasons and move southward,and under its combined effect with diabatic heating anomalies, the anomalous wave train of atmospheric circulation changes from an "east-west dipole" to a "PNA like" mode distribution, the upper and lower structures and intensities undergo a transition process of "equivalent positive pressure-weak oblique pressure-equivalent positive pressure" and "strong-slightly weakened-significantly strengthened", respectively; on the contrary, anomalous atmospheric circulation forces SSTA to transform from an "east-west dipole" to a "horseshoe shaped" distribution, undergoing a "strong-weak-weak" transition in intensity from early autumn (ASO) to early winter (OND). The North Pacific SSTA in early autumn (ASO) causes a significant increase in atmospheric circulation anomalies in early winter (OND) through sustained effects and transient activity forcing, achieving statistical significance. The atmospheric circulation anomaly corresponding to the "PNA like mode" in early winter (OND) is a significant wave train propagating downstream to North America, which contributes to the formation of the intrinsic variability PNA mode in the winter atmosphere. When the atmospheric circulation anomaly in early winter (OND) is in the same (opposite) phase as the winter PNA mode, the PNA mode strengthens (weakens), and the changes in the strength of the PNA mode have certain indicative significance for predicting extreme weather in China.