"Response of the wintertime Northern Hemisphere atmospheric circulation to current and projected Arctic sea ice decline: a numerical study with CAM5," J. Climate (2013); doi: 10.1175/JCLI-D-13-00272.1

Journal of Climate, (2013); doi: 10.1175/JCLI-D-13-00272.1

Response of the wintertime Northern Hemisphere atmospheric circulation to current and projected Arctic sea ice decline: a numerical study with CAM5

Yannick Peings* and Gudrun Magnusdottir (Department of Earth System Science, University of California, Irvine, CA, U.S.A.)

Abstract

The wintertime Northern Hemisphere (NH) atmospheric circulation response to current (2007-2012) and projected (2080-2099) Arctic sea ice decline is examined with the latest version of the Community Atmospheric Model (CAM5). The numerical experiments suggest that the current sea ice conditions force a remote atmospheric response in late winter that favors cold land surface temperatures over mid-latitudes, as has been observed in recent years. Anomalous Rossby waves forced by the sea ice anomalies penetrate into the stratosphere in February and weaken the stratospheric polar vortex, resulting in negative anomalies of the Northern Annular Mode (NAM) that propagate downwards during the following weeks, especially over the North Pacific. The seasonality of the response is attributed to the timing of the phasing between the forced and climatological waves. When sea ice concentration taken from projections of conditions at the end of the 21st century is prescribed to the model, negative anomalies of the NAM are visible in the troposphere, both in early and late winter. This response is mainly driven by the large warming of the lower troposphere over the Arctic, as little impact is found in the stratosphere in this experiment. As a result of the thermal expansion of the polar troposphere, the westerly flow is decelerated and a weak but statistically significant increase of the mid-latitude meanders is identified. However, the thermodynamical response extends beyond the Arctic and offsets the dynamical effect, such that the stronger sea ice forcing has limited impact on the intensity of cold extremes over mid-latitudes.

*Correspondence: Dept. of Earth System Science, University of California, Irvine, Irvine, CA 92697-3100, ypeings@uci.edu

 

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-13-00272.1

K. Delthloff et al.,The climate system of the Earth from a polar perspective

Nuuk Climate Days 2009: Changes of the Greenland Cryosphere Workshop & The Arctic Freshwater Budget International Symposium, Nuuk, Greenland, 25-27 August 2009


Primary author: DELTHLOFF, Klaus (Alfred Wegener Institute for Polar and Marine Research (AWI),
Germany), Klaus.Dethloff@awi.de.  Co-authors: RINKE, A. (Alfred Wegener Institute for Polar and Marine Research); HANDORF, D. (Alfred Wegener Institute for Polar and Marine Research); DORN, W. (Alfred Wegener Institute for Polar and Marine Research); BRAND, S. (Alfred Wegener Institute for Polar and Marine Research); MIELKE, M. (Alfred Wegener Institute for Polar and Marine Research); GRAESER, J (Alfred Wegener Institute for Polar and Marine Research); HERBER, A. (Alfred Wegener Institute for Polar and Marine Research)

Abstract ID: F1

The climate system of the Earth from a polar perspective

Balloon and radio sounding data from the North Pole drifting station NP35 for autumn 2007 to spring 2008 have been used to evaluate numerical model outputs (simulations with the regional climate model HIRHAM, ECMWF analyses). HIRHAM in the climate mode has some difficulty to represent the observed complex temperature profile, while the forecast mode shows better agreement. Sensitivity experiments concerning the atmospheric initial state, sea ice thickness and planetary boundary layer parameterization demonstrate improvements in the simulations.

Similar measurements have been carried out during spring 2009 on NP 36 and with the AWI airplane POLAR 5 over the Arctic Ocean. The pilot-project PAM-RCM (Pan-Arctic Measurements and Arctic Regional climate model simulations) provided a unique opportunity to obtain a snapshot of aerosol and cloud distributions and associated meteorological and atmospheric conditions as well as measurements of sea ice thickness in a latitude band between about 70°N and 80°N.

Sensitivity experiments using a coupled regional atmosphere-ocean-ice model of the Arctic has been conducted in order to identify the requirements needed to reproduce observed sea-ice conditions and to address uncertainties in the description of Arctic processes. While more sophisticated schemes for the albedo, the treatment of lateral freezing and melting, and the snow cover have been successfully introduced into the model, the parameterization of clouds is an open issue.

The global influence of Arctic feedbacks connected with sea-ice albedo changes and stratospheric ozone changes have been investigated. The simulations show significant changes over the Arctic and the whole globe due to changes of planetary wave patterns, which trigger the Arctic Oscillation (AO) and influences the sea -ice cover.

The impact of an interactive stratospheric ozone chemistry on the tropospheric circulation has been studied on the basis of the atmosphere-ocean-sea ice general circulation model ECHO-GiSP. The results show a sensitivity of the tropospheric circulation dynamics to the stratospheric chemistry. With enabled interactive stratospheric chemistry the model tends to the negative phase of the AO mode and a more unstable polar vortex..

Contact for symposium information:  Sune Nordentoft Lauritsen, e-mail: snl@space.dtu.dk