A New Method for Estimating Roughness Parameters and Evaluating the Quality of Observations

K. J. Schaudt The University of Arizona, Institute of Atmospheric Physics, Tucson, Arizona

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Abstract

A new method for estimating the roughness parameters (displacement height d, momentum roughness length zo, and friction velocity u∗), under adiabatic conditions, is introduced in this paper. The goals of this method are to obtain an unambiguous best fit for the roughness parameters and, perhaps, to reduce the present large uncertainties in these estimations via screening of the wind profile observations using a standard quality-of-fit measure. There are a number of advantages to this new method. Not only does it produce better fits (less error between predicted and observed values) than the two most commonly used methods but it also does so more effectively when the observations are of high quality. The standard wind profile equation is rewritten in a manner that allows linear least squares analysis to be performed unambiguously to determine the best fit values for dand zo for any given u∗. The u∗ is scanned to find the true best fit for all three parameters. The quality of fit, Q, of the parameters to the wind profile observations is also found. This quality of fit test is used beyond the normal test for adiabaticity to screen out the low-quality observations. Using only high-quality observations to estimate the roughness parameters should reduce the uncertainties. The purposes of this paper are to introduce the method, to illustrate how it improves the fit, and to make it known that a fortran program that performs this analysis is available by contacting the author for the World Wide Web address.

Corresponding author address: Dr. Kimberly J. Schaudt, Institute of Atmospheric Physics, The University of Arizona, PAS Building, #81, Tucson, AZ 85721.

schaudt@stratus.atmo.arizona.edu

Abstract

A new method for estimating the roughness parameters (displacement height d, momentum roughness length zo, and friction velocity u∗), under adiabatic conditions, is introduced in this paper. The goals of this method are to obtain an unambiguous best fit for the roughness parameters and, perhaps, to reduce the present large uncertainties in these estimations via screening of the wind profile observations using a standard quality-of-fit measure. There are a number of advantages to this new method. Not only does it produce better fits (less error between predicted and observed values) than the two most commonly used methods but it also does so more effectively when the observations are of high quality. The standard wind profile equation is rewritten in a manner that allows linear least squares analysis to be performed unambiguously to determine the best fit values for dand zo for any given u∗. The u∗ is scanned to find the true best fit for all three parameters. The quality of fit, Q, of the parameters to the wind profile observations is also found. This quality of fit test is used beyond the normal test for adiabaticity to screen out the low-quality observations. Using only high-quality observations to estimate the roughness parameters should reduce the uncertainties. The purposes of this paper are to introduce the method, to illustrate how it improves the fit, and to make it known that a fortran program that performs this analysis is available by contacting the author for the World Wide Web address.

Corresponding author address: Dr. Kimberly J. Schaudt, Institute of Atmospheric Physics, The University of Arizona, PAS Building, #81, Tucson, AZ 85721.

schaudt@stratus.atmo.arizona.edu

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