中高纬外强迫因子对夏季欧亚中高纬度阻塞环流的协同影响机理

The Eurasian blocking circulation anomalies over the mid-high latitudes during summer is one of the primary circulations associated with southern China droughts and floods. And the formulation of blocking circulation is closely related to atmospheric internal modes and external forcing factors which are playing an increasingly important role. In order to investigate the cause of blocking circulation anomalies on the interannual and decadal timescale, it is crucial to explore the impact of preceding external forcing factors and the mechanisms responsible for the influence. However, previous studies focus mainly on single external forcing factor as well as its influence, and far little attention has been paid to the combined impact of multiple factors. Therefore, in the present study, on the basis of critical processes in sea-land-air interaction, we attempt to identify the key external forcing factors, such as Arctic sea ice, Eurasian snow cover and North Atlantic sea surface temperature, and further to analyse the decadal changes in the relationship between key factors and circulation anomalies over the blocking domains. In view of the configuration of key factors, the physical mechanism responsible for the combined impact of key factors on the circulation anomalies over the blocking domains will be diagnosed by investigating the heating and transient vorticity forcing, via observational data and numerical simulation. Furthermore, the experienced forecast models would also be constructed. In the present project, we are beginning to get a deeper insights into the combined impact of preceding external forcing factors on the summer circulation anomalies over the Eurasian blocking domains. It aims to provide a scientific basis for improving the skill of summer climate forecast and thus increasing the ability to deal with disasters.

夏季欧亚中高纬阻塞环流异常是影响我国南方旱涝的关键环流之一。阻塞环流的形成与前期中高纬外强迫和大气内部因子变异紧密相关，其中外强迫因子起着越来越重要的作用。认识年际-年代际尺度阻塞环流异常成因，有必要探索前期外强迫多因子对它的影响机理。关于影响机理的研究，以往工作大多针对外强迫单因子，对多因子多尺度协同作用研究不足。因此，本课题基于海陆气相互作用的关键过程，首先识别影响阻塞环流的前期秋冬春季外强迫因子（北极海冰、欧亚大陆积/融雪和北大西洋海温），分析前期多因子与阻塞环流异常年际关系的年代际转变及其成因。然后考虑多因子相互配置，结合诊断分析和数值模拟，基于热力强迫和波流相互作用等物理过程，揭示前期外强迫多因子对阻塞环流的协同影响机理，建立相关经验预测模型。据此，本项目将建立外强迫多因子对阻塞环流异常的协同影响机理的深入认识，为提高我国夏季短期气候预测水平和国家开展防灾减灾工作提供科学依据。

夏季欧亚中高纬阻塞环流异常是影响我国夏季降水和旱涝的关键环流之一。阻塞环流的形成和变化与前期中高纬外强迫因子和大气内部因子变异紧密相关，其中外强迫因子起着越来越重要的作用。认识年际尺度阻塞环流异常成因，有必要探索外强迫对它的影响机理。关于影响机理的研究，以往工作大多针对外强迫单因子，对多因子协同作用研究不足。因此，本课题基于陆气相互作用等关键过程，系统研究了春季多个外强迫（北极海冰、欧亚大陆积/融雪和土壤湿度等）对夏季欧亚中高纬度大气环流和阻塞环流的影响，结合资料分析和数值模拟，揭示外强迫多因子影响阻塞环流的热力学和动力学物理机制，并建立相关经验预测模型。结果表明：（1）春季北极海冰的年际变化与夏季乌拉尔山阻塞高压频次正相关。极冰通过调制中纬度地区的天气尺度瞬变涡旋活动以及改变下垫面土壤湿度和热力条件，来影响乌拉尔山地区阻塞高压的建立和发展；（2）春末欧亚融雪也是调制夏季欧亚中高纬大气环流的关键因子，融雪通过改变春季-夏季土壤湿度及其相联系的热通量异常来激发异常Rossby波，进而加强了气候态准定常行星波2波和4波，其中乌拉尔山和鄂霍茨克海地区出现明显的高压脊，有利于阻塞高压的建立，为东亚夏季气候预测提供了理论依据；（3）春季北极海冰和欧亚积雪对欧亚遥相关型（EU）具有协同影响，二者皆可调制夏季EU型，表现为北大西洋-欧亚地区的“-+-+”遥相关波列，乌山阻塞高压明显偏弱，东亚大槽偏浅。基于冰雪两个因子建立的气候预测模型对夏季长江流域降水具有较强的预测能力；（4）回顾了中国南方降水和旱涝成因的主要研究进展，指出南方旱涝是热带太平洋海温、印度洋海温、青藏高原积雪等多因子协同影响的结果。据此，本项目加强了外强迫多因子影响阻塞环流异常的物理机制的深入认识，结果已经应用到国家气候中心亚洲区域气候监测诊断系统，为提高我国夏季短期气候预测水平和国家开展防灾减灾工作提供科学依据。