UBC Faculty Research and Publications

Application of Two-Dimensional Terrain Height Spectra to Mesoscale Modeling. Steyn, Douw G.; Ayotte, K. W.


A caution is offered with regard to the use of one-dimensional terrain spectra to indicate the grid resolution needed to resolve terrain forcing in mesoscale numerical modeling exercises. To illustrate this, two-dimensional terrain height spectra are presented for two contrasting terrains: a relatively direction free topography (a portion of southcentral British Columbia, Canada) and a highly ordered topography (a portion of the ridge and valley terrain in Pennsylvania). Isoamplitude plots of the two spectra show clearly the morphological differences between the two regions and indicate the degree of directionality of the ordered terrain. An investigation of the wavenumber dependence of the terrain height spectra shows the spectral roll-off for the first case to be essentially independent of direction and to decay roughly as wavenumber to the -5/2 power over a wavenumber range of 0.04 to 8.33 km−1. By contrast, the spectral roll-off in the second case is strongly dependent on direction with an exponent that may be either greater than or less than the convergence limit (−2.0 for the amplitude spectrum) indicated by Young and Pielke. Copyright 1985 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (http://www.ametsoc.org/) or from the AMS at 617-227-2425 or copyright@ametsoc.org.

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