北太平洋冬季西部发展型天气尺度涡旋对平均流的影响

在中纬度北太平洋大气强斜压区,存在频繁的天气尺度涡旋活动,通过水分、动量和能量输送维持大气环流。为了进一步研究天气尺度涡旋发生发展与大尺度环流之间的联系,利用1981—2013年再分析资料,筛选出西部发展型天气尺度涡旋114个偏强日和87个偏弱日,给出了西部发展型天气尺度涡旋异常导致的动力和热力强迫的变化,同时从能量转换的角度分析了西部发展型天气尺度涡旋与平均流之间的相互作用,并探讨了其与西太平洋遥相关型的关系。结果表明:西部发展型天气尺度涡旋通过动力强迫和热力强迫影响平均流,其中动力强迫主要造成北太平洋中纬度上空的西风气流加速并向北移动;热力强迫的作用则是减弱中纬度大气斜压性。同时,强西部发展型天气尺度涡旋有利于西北太平洋上空对流层低层斜压有效位能向扰动动能的转化增大和扰动动能向平均流的转化增大,有利于中纬度地区对流层高层平均流向扰动动能的转化增大。此外,西部发展型天气尺度涡旋通过与平均流的作用,对维持西太平洋遥相关型的负位相有一定影响。

Influence of western developing pattern synoptic-scale eddy on mean flow over North Pacific in wintertime

In the strong atmospheric baroclinic zone of the North Pacific at mid-latitude,the spread activities of synoptic-scale eddy are frequent,which maintain atmospheric circulation through the moisture,momentum and energy transport.In order to further study the relationship between the occurrence and development of synoptic-scale eddy and large-scale circulation,this paper selected 114 strong and 87 weak days of the western developing pattern synoptic-scale eddy (WSE) by using the reanalysis data from 1981 to 2013,and gave the variations of dynamic and thermal forcing caused by the WSE anomalies.Meanwhile,it analyzed the interaction between the WSE and mean flow from the perspective of energy transformation and the relationship between the WSE and the Western Pacific (WP) teleconnection pattern.Results show that the WSE affects mean flow through dynamic and thermal forcing.The dynamic forcing mainly makes the westerly currents over the mid-latitudes of North Pacific accelerate and move northward,while the thermal forcing weakens atmospheric baroclinicity over mid-latitudes.Meanwhile,the strong WSE is beneficial to increase the conversion of baroclinic available potential energy to eddy kinetic energy and eddy kinetic energy to mean flow in the lower troposphere over Northwest Pacific,and to increase the conversion of mean flow to eddy kinetic energy in the upper troposphere over mid-latitudes.In addition,the WSE has a certain effect on maintaining the negative phase of the WP teleconnection pattern through its interaction with the mean flow.