Land-Atmosphere Coupling in ACME with Subgrid Topography

Wednesday, May 6, 2015 - 07:00
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The ACME land and atmosphere models will use subgrid-scale topographic classes to better simulate the influence of orography on precipitation, temperature, land surface hydrology, glacier surface mass balance, and other physical processes. To permit more flexibility in choices of component grids and to allow the changing ice thickness to influence atmospheric processes, land-atmosphere coupling will be much more complex than a simple horizontal remapping between two grids. We have developed a coupling approach that uses vertical interpolation between adjacent elevation classes to optimize accuracy, along with normalization procedures to ensure exact conservation of energy. This approach can be applied not only to static topographic units in the land model, but also to glacier columns whose elevation and area change in time. Here we outline the main ideas, discuss the merits and drawbacks of different approaches to remapping and normalization, and describe the software changes needed to support accurate, conservative coupling.