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Dynamics of Arctic Climate and Circulation

PI: Eric DeWeaver
Institution: University of Wisconson-Madison
Additional Investigators: Qingfang Wu
Abstract:
The first priority of the proposed intercomparison is to look at the annual cycle of the sea level pressure pattern over the Arctic and sub-Arctic. Motivation for the SLP comparison comes from Bitz et al. (2002), who found that model biases in geostrophic surface circulation have a profound effect on the distribution of Arctic sea ice. Holland and Bitz (in press at Climate Dynamics) further showed that sea ice biases in present-day climate simulations are linked to the extent of polar amplification in global warming simulations.

In addition to the SLP and surface circulation intercomparison, I plan to use eddy temperature, geopotential height, potential vorticity, and streamfunction to examine the three-dimensional structure of the flow associated with the SLP centers, particularly the Beaufort High. In reanalysis, the Beaufort High is the surface expression of a deep barotropic high rather than a surface-trapped feature associated with cold lower-tropospheric temperatures. Simulations of the high will be more credible -- and less sensitive to local surface temperature change -- if they can reproduce this deep vertical structure.

I also plan to look at the dynamical processes which maintain the high-latitude circulation. In particular, I would like to compare the strength of the synoptic and submonthly fluxes of heat and momentum among the models, and the strength of the diabatic heating. In CCSM3 I have found that synoptic momentum flux is overestimated by a factor of two or more, and I'm interested in the possibility that this is a common AGCM bias.

Model data required:

* monthly-mean surface and 3-d circulation fields -- SLP, winds, temperature, geopotential height.

* sub-monthly eddy flux statistics (uu, uv, vv, vt, wt).

* total diabatic heating.

* 6-hourly or once-daily horizontal winds and temperature at an upper level, winds and temperature at a lower level, and SLP.
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