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Second-order closure PBL model with new third-order moments: Comparison with LES dataThis paper contains two parts. In the first part, a new set of diagnostic equations is derived for the third-order moments for a buoyancy-driven flow, by exact inversion of the prognostic equations for the third-order moment equations in the stationary case. The third-order moments exhibit a universal structure: they all are a linear combination of the derivatives of all the second-order moments, bar-w(exp 2), bar-w theta, bar-theta(exp 2), and bar-q(exp 2). Each term of the sum contains a turbulent diffusivity D(sub t), which also exhibits a universal structure of the form D(sub t) = a nu(sub t) + b bar-w theta. Since the sign of the convective flux changes depending on stable or unstable stratification, D(sub t) varies according to the type of stratification. Here nu(sub t) approximately equal to wl (l is a mixing length and w is an rms velocity) represents the 'mechanical' part, while the 'buoyancy' part is represented by the convective flux bar-w theta. The quantities a and b are functions of the variable N(sub tau)(exp 2), where N(exp 2) = g alpha derivative of Theta with respect to z and tau is the turbulence time scale. The new expressions for the third-order moments generalize those of Zeman and Lumley, which were subsequently adopted by Sun and Ogura, Chen and Cotton, and Finger and Schmidt in their treatments of the convective boundary layer. In the second part, the new expressions for the third-order moments are used to solve the ensemble average equations describing a purely convective boundary laye r heated from below at a constant rate. The computed second- and third-order moments are then compared with the corresponding Large Eddy Simulation (LES) results, most of which are obtained by running a new LES code, and part of which are taken from published results. The ensemble average results compare favorably with the LES data.
Document ID
19950028426
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Canuto, V. M.
(NASAGoddard Inst. for Space Studies, New York, New York United States)
Minotti, F.
(NASAGoddard Inst. for Space Studies, New York, New York United States)
Ronchi, C.
(NASAGoddard Inst. for Space Studies, New York, New York United States)
Ypma, R. M.
(NASAGoddard Inst. for Space Studies, New York, New York United States)
Zeman, O.
(Stanford Univ. Stanford, CA, United States)
Date Acquired
August 16, 2013
Publication Date
June 15, 1994
Publication Information
Publication: Journal of the Atmospheric Sciences
Volume: 51
Issue: 12
ISSN: 0022-4928
Subject Category
Meteorology And Climatology
Accession Number
95A60025
Distribution Limits
Public
Copyright
Other

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