The Linkage between Midwinter Suppression of the North Pacific Storm Track and Atmospheric Circulation Features in the Northern Hemisphere

Abstract

The midwinter suppression (MWS) of the North Pacific storm track (NPST) has been an active research topic for decades. Based on the daily-mean NCEP/NCAR reanalysis from 1948 to 2018, this study investigates the MWS-related atmospheric circulation characteristics in the Northern Hemisphere by regression analysis with respect to a new MWS index, which may shed more light on this difficult issue. The occurrence frequency of the MWS of the upper-tropospheric NPST is more than 0.8 after the mid-1980s. The MWS is accompanied by significantly positive sea-level pressure anomalies in Eurasia and negative anomalies over the North Pacific, which correspond to a strengthened East Asian winter monsoon. The intensified East Asian trough and atmospheric blocking in the North Pacific as well as the significantly negative low-level air temperature anomalies, lying upstream of the MNPST, are expected to be distinctly associated with the MWS. However, the relationship between the MWS and low-level atmospheric baroclinicity is somewhat puzzling. From the diagnostics of the eddy energy budget, it is identified that the inefficiency of the barotropic energy conversion related to the barotropic governor mechanism does not favor the occurrence of the MWS. In contrast, weakened baroclinic energy conversion, buoyancy conversion, and generation of eddy available potential energy by diabatic heating are conducive to the occurrence of the MWS. In addition, Ural blocking in the upstream region of the MNPST may be another candidate mechanism associated with the MWS.

摘要

虽然大气斜压性在冬季达到最强,北太平洋风暴轴强度在深冬时期(1月和2月)却弱于秋季和春季,由于不符合斜压不稳定理论的预期,这被称为北太平洋风暴轴“深冬抑制”(MWS)现象。本文利用再分析资料研究了与北太平洋风暴轴MWS相关联的北半球大气环流特征。对流层高层北太平洋风暴轴MWS的发生频率在1980s中期的年代际减弱之后仍超过0.8。MWS伴随着海平面气压在欧亚大陆有显著的正异常,在北太平洋有显著的负异常,加强的东-西气压梯度可能对应增强的东亚冬季风。显著增强的东亚大槽和北太平洋阻塞,以及位于北太平洋风暴轴上游显著的低层冷异常与MWS存在联系。然而,MWS与低层大气斜压性的关系令人困惑。从瞬变涡旋能量收支的诊断可知,低效的正压能量转换不利于MWS发生,减弱的斜压能量转换、浮力转换和由非绝热加热引起的瞬变涡旋有效位能有利于MWS发生。此外,北太平洋风暴轴上游的乌拉尔阻塞也可能与MWS存在联系。