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Distinct circulation states of the Arctic atmosphere induced by natural climate variability

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Dorn, W. , Dethloff, K. , Rinke, A. and Botzet, M. (2000): Distinct circulation states of the Arctic atmosphere induced by natural climate variability , Journal of Geophysical Research - Atmospheres, Vol. 105, No. D24, pp. 29659-29668 . doi: 2000JD900546
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2000JD900546
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Abstract:

The high-resolution regional climate model HIRHAM4 with a horizontalresolution of 0.5 degrees times 0.5 degrees was used to determine theinfluence of natural climate variations in the Arctic. The large-scalelateral forcing and the lower boundary forcing for the HIRHAM4 weredelivered from a long-term run of the coupled circulation model ECHO-Gat T30 resolution. This run was carried out with prescribed constantexternal forcing for present-day climate conditions. 600 years of thisECHO-G simulation were analyzed to find periods persisting over severalyears either with mainly warm or mainly cold conditions during the Arcticwinter. Two warm and two cold periods, each of 6 years duration, wereselected for the regionalization of the Arctic climate in January. Theperformed model simulations show that a warm or cold Arctic winterclimate is connected with two distinct circulation states of the Arcticatmosphere. These states are characterized by a different location andextension of the tropospheric vortex with a vortex center over thewestern Arctic in warm Januaries or over the eastern Arctic in coldJanuaries, respectively. Moreover, there are indications that thesedifferent locations of the vortex are linked to a different synopticactivity in Alaska and the eastern part of the Arctic which is, in turn,related to a different meridional transport of heat and moisture intothese regions. The resultant climate conditions in these regions differfrom each other with statistical significance and are, finally, decisivefor the warm or cold Arctic climate state.

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