Verification tests of the ETA model, October-November 1988

"The sigma system introduced at the early stage of numerical weather prediction has enabled a simple representation of the effect of mountains and has become almost universally accepted. Concern has however persisted over the possibility of large errors in calculation of the pressure gradient force over steep terrain slopes in some situations, and errors also may occur or are known to occur in the horizontal advection and lateral diffusion. Experience shows that sigma system models do indeed have difficulties with very steep mountains thus it is a common practice to smooth terrain elevations before they are incorporated into NWP models. This however reduces the barrier effect of model mountains and/or the ability of the model to capture the influence of smaller scale terrain features"--Introduction. Fedor Mesinger, Thomas L. Black. "March 1989." System requirements: Adobe Acrobat Reader. Includes bibliographical references (page 46-47). 1989 NWS (National Weather Service) NCEP (National Centers for Environmental Prediction) Library Public Domain 2285