资源环境科技发展态势分析平台

Cold air outbreaks (CAOs) are the dominant cause of intense wintertime upward heat fluxes in the Irminger Sea. In this study, the climatological pathways of Irminger Sea CAO airmasses and the evolution of airmass properties, as well as the large-scale synoptic environments leading to CAO formation are examined for winter. To that end, a comprehensive, multi-decadal climatology of Irminger Sea CAO airmasses using kinematic trajectories is presented, complemented by a composite analysis of the large-scale synoptic environment for intense CAO events.

The following three synoptic environments conducive for CAO formation are identified: (1) The westerly environment is characterized by an upper-level trough crossing Greenland and inducing strong westerly winds at crest level, accompanied by either cyclogenesis or the intensification of an existing cyclone in the lee of Greenland. The associated CAO airmasses originate in the Canadian Arctic, overflow southern Greenland, and descend into the Irminger Sea with an according imprint in their thermodynamic evolution. (2) In the easterly cyclonic environment, one or multiple cyclones in the Nordic Seas induce northerly winds along Greenland's eastern coast that transport Arctic airmasses from Fram Strait to Denmark Strait. (3) The easterly anti-cyclonic environment, finally, is dominated by an anti-cyclone over Greenland with similar airmass origins and pathways as in the easterly cyclonic environment. The two easterly environments represent the limiting cases of an intermediate spectrum, whereas in contrast the westerly environment is clearly distinct. Katabatic drainage from northern Greenland contributes to the CAO airmasses in both easterly environments, whereas in the easterly cyclonic environment also marine airmasses from the Nordic Seas are involved. An important conclusion of this study is that the amount of heat extracted from the ocean by a CAO airmass depends critically on its pathway, and thus on the synoptic environment.