资源环境科技发展态势分析平台

Winter weather in the subarctic and lower latitudes can be influenced by the repositioning of the polar vortex away from being centred near the North Pole, extending over regional locations of subarctic continents. One example was the "Beast from the East" event in Eurasia in March 2018, which brought snow to much of Europe. We are interested in extended (week to a month) North American weather events, and especially the impacts from a location of the polar vortex centre over and near Greenland. For a tropospheric polar vortex location index, we use low 500hPa geopotential heights (GPH) over greater Greenland from values of the Greenland Blocking Index (GBI) below negative 1.0 SD (1951-2018 base period). February is a preferred month with 10 low GBI events beginning 1989. Composite 100 and 500hPa GPH for these 10 cases show hemispheric-wide features with a trough/ridge/trough pattern extending from eastern Siberia eastward to Greenland and spanning both the stratospheric and tropospheric polar vortex. Associated extreme weather as seen in 2015 and 2018 include cold temperatures on the eastern United States, warm monthly temperatures (>5.0 degrees C anomalies) in California with drought conditions, and record sea ice loss in the winter Bering Sea. Results support the concept that November-December has a regional tropospheric pathway for Arctic/mid-latitude weather interactions due to delayed autumn sea ice freeze up, whereas January-March has a more hemispheric pathway related to stratospheric polar vortex movement that is delayed into late winter.