Climate Modeling

Atmospheric Circulation and Mountain Orography

Ice sheet-climate feedbacks

Gerard Roe, UW Quaternary Research Center
Collaborator: Dick Lindzen, MIT

Continental-scale ice sheets influence the atmospheric circulation

We have demonstrated the strong coupling that existed between the great continental ice sheets of the ice ages and the atmospheric circulation. The ice sheets induced changes in the atmospheric stationary waves and in the distribution of precipitation. These changes in turn acted to sculpt the ice sheets over thousands of years.

Figure 1:Continental-scale ice sheets influence the atmospheric circulation. In turn the atmospheric circulation determines the patterns of accumulation and ablation which shape the ice sheet. This feedback has been explored using a hierachy of idealized atmospheric and ice sheet models, and it must have contributed to the configuration of the great ice sheets of the Pleistocene ice ages.

Orographic precipitation and the evolution of mountain ranges

Collaborators: Dave Montgomery and Bernard Hallet, QRC
Todd Elhers, Caltech
Bob Houze and Dale Durran, UW Atmospheric Sciences

Active mountain ranges are, to first order, the result of uplift due to tectonic convergence and erosion due to bedrock incision by streams and rivers. Our results show that the spatial distribution of precipitation is of crucial importance in setting the relief in mountainous regions. The interaction is a feedback because the precipitation which acts to shape the mountains is itself a function of the interaction between the mountain topography and the prevailing atmospheric winds. We are currently extending this work to more complete surface process models, and to examining the specifics of different precipitation regimes, and the impact on observed mountain ranges.

Figure 2

Figure 2: The form and structure of earth's mountain ranges are a result of the combined action of tectonics, erosion, and climate, although the latter has frequently been neglected in quantitative studies. To first order, an active mountain range is the result of the competition between uplift due to tectonic convergence and erosion due to rivers incising into bedrock channels. The rivers are obviously fed by precipitation and a fundamental feature of mountainous terrain is highly variable spatial patterns of precipitation. These patterns are caused in turn by the interaction between the prevailing atmospheric circulation and the mountain topography. Model calculations show that such patterns are a first order control on mountain orography.

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