Intra-Seasonal Features of Winter Extreme Cold Events in Northeast–North China and Synergistic Effects of Circulation Systems in Mid-High Latitude

Based on the daily minimum air temperature (Tmin) data from China Meteorological Data Network and NCEP/DOE reanalysis data, intra-seasonal circulation characteristics evolution of extreme cold events (ECEs) in Northeast–North (NE-N) during winter 1979–2018 are explored, synergistic effects key systems mid-high latitude ECEs discussed. The results show that: (1) Tmin NE-N region presents a significant low-frequency period 10–30 d; cooling phases, pair cyclone–anticyclone lower troposphere moves southeastward, accompanying intensifying Siberian High, leads to abnormal northerly; developing wave trains middle result enhancing maintaining air; furthermore, situation upper tropospheric jet weakening north strengthening south is favorable for move southward accumulate region. (2) There two Eurasian at 200 hPa level. one southeastward through Ural Mountains coast East Asia, with upstream activity flux dispersing region, causing northeast vortex develop. relatively weak intensity disperses northward, enhances vortex. (3) Mountain Blocking Northeast Cold Vortex, Asian Subtropical Jet. High four phases earlier than low temperature, rest basically phase temperature. effect will lead extended-range