Representing Effects of Complex Terrain on Mountain Meteorology and Hydrology

Abstract:

Thermodynamic and microphysical processes in the atmosphere are sufficiently fast that the effects of complex terrain on mountain meteorology are evident at spatial scales less than ten kilometer, much smaller than the resolution of most global atmosphere models. The resulting orographic signatures in air temperature and precipitation influence the surface hydrology of mountain watersheds. To account for these effects in global models, we build on a method developed first for a regional climate model in the 1990s and applied to only one global model in the 2000s. The mean surface elevation and fractional area of a moderate set of subgrid elevation classes is determined based on high-resolution Digital Elevation Model and a percentile-area classification scheme. This information is applied to a simple model of airflow over topography to determine the vertical displacement of air parcels passing through the grid cell. Conservation of energy and water determines the temperature and humidity profiles that drive subgrid predictions of thermodynamics for each elevation class that provides atmospheric forcing for the land model that in turn simulates surface states and fluxes as lower boundary conditions for the atmosphere model. All of the atmospheric and land surface physics is applied to each elevation class. Results can be distributed geographically according to the distribution of surface elevation at high spatial resolution. We will demonstrate the performance in the DOE ACME model.