An empirical expression for aerodynamic resistance in the unstable boundary layer |
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Authors: | Neil R Viney |
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Institution: | (1) Mathematics Department, University College, University of New South Wales, 2600 Canberra, A.C.T., Australia |
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Abstract: | In unstable conditions, the set of equations defining the aerodynamic resistance to sensible heat transfer, r
a
, cannot be solved analytically. An iterative technique must be used to obtain r
a
exactly, but this is cumbersome and time consuming. In this paper, a new, empirical equation is presented relating the ratio, Q, of the aerodynamic resistances in neutral and unstable conditions, to the bulk Richardson number, Ri
B
. The equation takes the form Q = a + b(–Ri )
c
, where a, b and c are empirical functions of (z – d)/z
om
. This model is shown to predict r
awith a mean absolute error of 0.06 s m–1 over the ranges -15 < Ri
B
< 0 and 10 < (z – d)/z
om
< 2300. Statistical comparison with other equations that have been proposed for r
a
in unstable conditions indicates the superior precision of the model presented here. |
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Keywords: | |
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