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A family of terrain-following theta-sigma hybrid vertical coordinates
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2002
[PDF-579.50 KB]
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Description:We investigate an algebraically simple family of hybrid vertical coordinates which possess the advantages of isentropic coordinates at high elevations but gradually and smoothly make the transition to terrain-following coordinates at the lower levels. The family of coordinates has parameters by which we can choose the approximate elevation characteristic of the broad transition between isentropic and terrain-following behavior, or the degree of 'dilution' of the coordinates at upper levels with 'sigma'. We illustrate the effects of these parameters on the vertical distribution of hybrid coordinate levels and we estimate the relative magnitudes of numerical truncation error associated with the calculation of the horizontal pressure gradient force as the result of using either pressure and geopotential or Montgomery potential and potential temperature as dependent variables. We claim no special merits for the particular family of hybrid coordinates we have employed here; rather we have used a relatively simple parameterized family as representative of a much larger class of hybrids, in the hope that the qualitative conclusions drawn from this study have a validity that extends more generally.
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Rights Information:Public Domain
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Compliance:Submitted
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