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Gunter Weller

Abstract

The surface energy balance in Antarctica is examined by summarizing and comparing field data collected at seven locations in five latitudinal zones, each having different ice surface characteristics which are specified. Satellite records are used to estimate the energy balance of the pack ice zone for which no field data are available. The midwinter energy loss from the ocean to the atmosphere of this zone may be almost an order of magnitude higher than previous estimates, due to a much larger extent of open water as determined from satellite observations. Interannual variations of the energy balance over the continent appear to be small, as judged from the limited data set, but the effects of sea ice, the largest year-to-year variable in the energy balance, could not be determined without better satellite-derived information of the sea ice thickness distribution.

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Gunter Weller and Bjorn Holmgren

Abstract

The microclimates of the arctic tundra at Barrow, Alaska, are described for the near-surface terrestrial layers in which most biological activities take place. Temperature profiles are constructed from detailed measurements in the air, vegetation and soil, from 16 m above to 6 m below the tundra surface. Wind and radiation measurements supplement these data. Considering the tundra as a two-dimensional heat exchange surface, daily components of the heat balance are computed and summarized for a number of periods throughout the year, which are characterized by changes of the physical nature of the tundra surface such as appearance and disappearance of snow, meltwater and precipitation, and growth and decay of vegetation. Through changes in surface terrain parameters such as albedo and roughness length, and availability of water for phase changes, the thermal and moisture regimes of the near-surface layer change markedly during these periods as reflected by the heat balance.

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John E. Walsh, Hiroshi L. Tanaka, and Gunter Weller
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Gunter Weller and Eugene W. Bierly
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Amanda H. Lynch, William L. Chapman, John E. Walsh, and Gunter Weller

Abstract

An Arctic region climate system model has been developed to simulate coupled interactions among the atmosphere, sea ice, ocean, and land surface of the western Arctic. The atmospheric formulation is based upon the NCAR regional climate model RegCM2, and includes the NCAR Community Climate Model Version 2 radiation scheme and the Biosphere–Atmosphere Transfer Scheme. The dynamic–thermodynamic sea ice model includes the Hibler–Flato cavitating fluid formulation and the Parkinson–Washington thermodynamic scheme linked to a mixed-layer ocean.

Arctic winter and summer simulations have been performed at a 63 km resolution, driven at the boundaries by analyses compiled at the European Centre for Medium-Range Weather Forecasts. While the general spatial patterns are consistent with observations, the model shows biases when the results are examined in detail. These biases appear to be consequences in part of the lack of parameterizations of ice dynamics and the ice phase in atmospheric moist processes in winter, but appear to have other causes in summer.

The inclusion of sea ice dynamics has substantial impacts on the model results for winter. Locally, the fluxes of sensible and latent heat increase by over 100 W m−2 in regions where offshore winds evacuate sea ice. Averaged over the entire domain, these effects result in root-mean-square differences of sensible heat flux and temperatures of 15 W m−2 and 2°C. Other monthly simulations have addressed the model sensitivity to the subgrid-scale moisture treatment, to ice-phase physics in the explicit moisture parameterization, and to changes in the relative humidity threshold for the autoconversion of cloud water to rainwater. The results suggest that the winter simulation is most sensitive to the inclusion of ice phase physics, which results in an increase of precipitation of approximately 50% and in a cooling of several degrees over large portions of the domain. The summer simulation shows little sensitivity to the ice phase and much stronger sensitivity to the convective parameterization, as expected.

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