Further Studies Of Atmospheric Turbulence In Layers Near The Surface: Scaling The Tke Budget Above The Roughness Sublayer |
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| Authors: | Paul Frenzen Christoph A Vogel |
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| Institution: | (1) 263 Kala Heights Drive, Port Townsend, WA 98368, USA;(2) NOAA Atmospheric Turbulence and Diffusion Division, Oak Ridge, TN 37831, USA |
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| Abstract: | The second of two experimental studies of the TKE budget conducted on sites of different roughness is described, and results are compared. The first took place within a shallow layer above a small field of mostly bare, cultivated soil; the second was carried out above a roughness sublayer of significant depth on an extensive plain of tall dry grass. Budget terms observed in the second study were scaled with a modified u which compensated for effects of an unusually large stress gradient and ensured that the  m functions would be collinear. By showing that the modification becomes negligible in smaller gradients, it is demonstrated that in normal conditions, budgets observed above significant roughness sublayers should be normalized by scaling in terms of the unreduced Reynolds stress at the sublayer's upper surface. This procedure is shown to be consistent with the expectation that TKE budgets in layers near the surface all scale in fundamentally the same way.Other findings include: (1) the fact that most m functions previously reported are not quite collinear is attributed to a type of overspeeding known to affect three-cup anemometers; (2) revised m functions, collinear and largely free of the effects of overspeeding, are determined from a well-established characteristic of the linear m relation for the stable case; (3) data that define collinear m functions can also be represented with single hyperbolic curves; (4) dissipation is found to be 10 to 15% too small to balance total TKE production in unstable and neutral conditions and to decrease with increasing z/L in thestable regime; and (5) new relations for  based on the observed behaviour of the dissipation deficit provide an improved closure for the set of equations that express the budget terms as functions of m and z/L. |
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| Keywords: | Atmospheric turbulence Cup anemometer overspeeding Dimensionless shear function (or  m)" target="_blank">gif" alt="phgr" align="MIDDLE" BORDER="0">m) Roughness sublayer Turbulence dissipation deficit Turbulence scaling Turbulent kinetic energy (or TKE) budget |
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