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

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 the strengthened East Asian winter monsoon. The intensified East Asian trough and North Pacific atmospheric blocking as well as significantly negative low-level air temperature anomalies accompanied by anomalous northerlies lying upstream of the MNPST are expected to be associated with the distinct 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, the strengthened 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 associated with the MWS.