Large ensembles of uncoupled and coupled model experiments on the influence of Arctic sea ice decline on mid-latitude weather and climate


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Tido.Semmler [ at ] awi.de

Abstract

We have conducted a series of atmosphere-only and coupled model experiments on time scales from weather to climate and with different methods to address the question how the large scale circulation of the Northern mid-latitudes is affected by the shrinking Arctic sea ice as well as by the overlying atmosphere. A major pathway has been found from the Barents Sea / Kara Sea area to Eastern Europe and Northern Asia and a secondary one from the Canadian Arctic into North America. In contrast, the atmosphere above ocean areas is less affected by the Arctic. A recurring response feature to declined Arctic sea ice is the slowdown and southward shift of the jet stream with less cyclone activity north of it leading to around 0.5 K colder conditions over some limited regions of North America and North Siberia in winter consistent with a negative Arctic Oscillation index. This happens despite the tendency of less intense cold advection due to the warmer Arctic in cases of anomalous northerly flow. It should be noted that for robust responses large ensemble simulations are needed due to low signal-to-noise ratio. In this respect it has been proven helpful to perform simulations in a Numerical Weather Prediction setting as the short simulation time enables us to easily run ensembles of several hundreds of realizations. Furthermore, in such a setting the initial response to a suddenly changed Arctic sea ice cover can be studied giving us hints how anomalies in the atmosphere develop. Coupled model simulations hint at no discernable influence of shrinking Arctic sea ice on the ocean on time scales of a year while on decadal to centennial time scales the ocean starts to react with possible feedbacks to the atmosphere. Due to less and thinner sea ice cover the momentum flux into the ocean increases which spins up the Beaufort Gyre. This response propagates towards the North Atlantic as an increased outflow through the Fram Strait, which drives increased volume transport into the Barents Sea, thus fostering the Atlantification of the basin. The response is not confined to the interior of the Arctic and our results suggest that it may reach as far south as the North Atlantic Current as a combined response to the dynamical ocean adjustment triggered within the Arctic and, secondarily, to the atmospheric weakening of the westerly winds.



Item Type
Conference (Poster)
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Primary Division
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Peer revision
Not peer-reviewed
Publication Status
Published
Event Details
Polar Climate Change: Driving Processes, Extreme Events, and Global Linkages, 23 Oct 2017 - 24 Oct 2017, Nanjing, China.
Eprint ID
46084
Cite as
Semmler, T. , Jung, T. , Campos, C. , Kasper, M. , Stulic, L. and Tilinina, N. (2017): Large ensembles of uncoupled and coupled model experiments on the influence of Arctic sea ice decline on mid-latitude weather and climate , Polar Climate Change: Driving Processes, Extreme Events, and Global Linkages, Nanjing, China, 23 October 2017 - 24 October 2017 .


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