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- Author or Editor: S. P. S. Arya x
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Abstract
The free convection similarity theory is examined in the light of recent observations in the atmosphere, convection chambers and wind tunnels. The theory describes the fluctuations of temperature and vertical velocity fairly well, but only in flows with finite shear. The horizontal components of velocity and mean temperature may not be scaled by the same in the range of stability ordinarily encountered in the surface layer of the atmosphere. Free convection similarity scaling of the outer layer is expected to be more successful, although sufficient atmospheric data are not available to test this assertion. Preliminary results of numerical calculations by Deardorff are very encouraging, and so are our limited observations in a wind tunnel boundary layer. Because of extremely variable conditions in the atmosphere under free convection, some aspects of this flow may be better studied in the laboratory under carefully controlled conditions. Both convection chamber (no shear) and wind tunnel (finite shear) flows have been used for this purpose; the latter is shown to give better similarity with the atmospheric boundary layer.
Abstract
The free convection similarity theory is examined in the light of recent observations in the atmosphere, convection chambers and wind tunnels. The theory describes the fluctuations of temperature and vertical velocity fairly well, but only in flows with finite shear. The horizontal components of velocity and mean temperature may not be scaled by the same in the range of stability ordinarily encountered in the surface layer of the atmosphere. Free convection similarity scaling of the outer layer is expected to be more successful, although sufficient atmospheric data are not available to test this assertion. Preliminary results of numerical calculations by Deardorff are very encouraging, and so are our limited observations in a wind tunnel boundary layer. Because of extremely variable conditions in the atmosphere under free convection, some aspects of this flow may be better studied in the laboratory under carefully controlled conditions. Both convection chamber (no shear) and wind tunnel (finite shear) flows have been used for this purpose; the latter is shown to give better similarity with the atmospheric boundary layer.
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Abstract
The effects of baroclinity and the scale-height ratio on the drag laws of the planetary boundary layer (PBL) are examined theoretically and compared to those of stability. The similarity drag relations using surface geostrophic winds are found to be more sensitive to these parameters than the drag relations based on the layer-averaged winds. Since baroclinity can be more safely ignored in the latter, these are considered more suitable for parameterizing the PBL in general circulation models. The geostrophic drag relations based on the generalized similarity theory are used to explain (simulate) the observed increasing trend of the surface cross-isobar angle in going toward the equator. It is shown that this trend is partly due to the change in the scale-height ratio and partly due to baroclinity. Clarke and Mess (1975), on the other hand, have suggested that baroclinity is wholly responsible for this trend. It is shown here that baroclinity effects are very much exaggerated in their formulation.
Abstract
The effects of baroclinity and the scale-height ratio on the drag laws of the planetary boundary layer (PBL) are examined theoretically and compared to those of stability. The similarity drag relations using surface geostrophic winds are found to be more sensitive to these parameters than the drag relations based on the layer-averaged winds. Since baroclinity can be more safely ignored in the latter, these are considered more suitable for parameterizing the PBL in general circulation models. The geostrophic drag relations based on the generalized similarity theory are used to explain (simulate) the observed increasing trend of the surface cross-isobar angle in going toward the equator. It is shown that this trend is partly due to the change in the scale-height ratio and partly due to baroclinity. Clarke and Mess (1975), on the other hand, have suggested that baroclinity is wholly responsible for this trend. It is shown here that baroclinity effects are very much exaggerated in their formulation.
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Abstract
It is pointed out that in a rotating frame of reference, the friction force on a fluid element may not be parallel and opposite to the velocity vector, as commonly depicted in textbook schematics of the force balance in the friction layer. A better schematic representation of the same is suggested here.
Abstract
It is pointed out that in a rotating frame of reference, the friction force on a fluid element may not be parallel and opposite to the velocity vector, as commonly depicted in textbook schematics of the force balance in the friction layer. A better schematic representation of the same is suggested here.
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No abstract available.
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Abstract
The results from some of the latest experimental and theoretical studies of the planetary boundary layer (PBL) ire used to revise certain better known schemes (Clarke, 1970b; Deardorff, 1972b) of parameterizing the boundary layer in general circulation models (GCM's). For high-resolution models, our proposed scheme is based on the surface layer similarity theory relations derived by Businger et al. (1971) from the Kansas tower data. For low-resolution GCM'S, the proposed scheme is based on the generalized PBL-similarity theory with the various similarity functions evaluated from the best available numerical models of the boundary layer. The usual practice of specifying a single value for the roughness parameter (z 0) for all the land surfaces in a GCM is questioned. The specified z 0 value at each grid point should actually reflect the roughness characteristics of the surface represented by it.
Abstract
The results from some of the latest experimental and theoretical studies of the planetary boundary layer (PBL) ire used to revise certain better known schemes (Clarke, 1970b; Deardorff, 1972b) of parameterizing the boundary layer in general circulation models (GCM's). For high-resolution models, our proposed scheme is based on the surface layer similarity theory relations derived by Businger et al. (1971) from the Kansas tower data. For low-resolution GCM'S, the proposed scheme is based on the generalized PBL-similarity theory with the various similarity functions evaluated from the best available numerical models of the boundary layer. The usual practice of specifying a single value for the roughness parameter (z 0) for all the land surfaces in a GCM is questioned. The specified z 0 value at each grid point should actually reflect the roughness characteristics of the surface represented by it.
Abstract
A critical assessment is made of the various diagnostic relations for the height of the nocturnal boundary layer, as well as of their past comparisons with experimental data. The parametric relations involving the characteristics of the whole boundary layer are found to be less satisfactory than those involving only the surface layer variables. The latter are tested against the Cubauw tower data for the selected winter periods when the mixed-layer height h was measured directly with an acoustic sounder. It is found that h has rather poor correlation with the height ho to which the effect of surface cooling extends. Its correlation with hu , the height of the maximum in wind speed, is fair (r ≈ 0.5) during strong stability conditions, but poor in slight to moderate stability conditions. Better correlations (r ≈ 0.7) are obtained with u */f, (u * L/f)1/2 and Deardorff's (1972b) interpolation formula where u * is the friction velocity, L is the Obukhov length and f the Coriolis parameter. The parametric relations based on the linear regression of h with the above height parameters are given. These may be used in the absence of direct measurements of h, especially when the type of information required for using a more accurate prognostic rate equation is not available.
Abstract
A critical assessment is made of the various diagnostic relations for the height of the nocturnal boundary layer, as well as of their past comparisons with experimental data. The parametric relations involving the characteristics of the whole boundary layer are found to be less satisfactory than those involving only the surface layer variables. The latter are tested against the Cubauw tower data for the selected winter periods when the mixed-layer height h was measured directly with an acoustic sounder. It is found that h has rather poor correlation with the height ho to which the effect of surface cooling extends. Its correlation with hu , the height of the maximum in wind speed, is fair (r ≈ 0.5) during strong stability conditions, but poor in slight to moderate stability conditions. Better correlations (r ≈ 0.7) are obtained with u */f, (u * L/f)1/2 and Deardorff's (1972b) interpolation formula where u * is the friction velocity, L is the Obukhov length and f the Coriolis parameter. The parametric relations based on the linear regression of h with the above height parameters are given. These may be used in the absence of direct measurements of h, especially when the type of information required for using a more accurate prognostic rate equation is not available.
Abstract
The similarity which exists between the stably stratified atmospheric boundary layer and a wind tunnelboundary layer developing over a cold plate is illustrated. It is shown that mean flow and turbulence characteristics in the near wall region of the stratified boundary layer are well described by Monin and Obukhovssimilarity theory, and that this theory provides a good basis for modeling in the laboratory of similar characteristics of the atmospheric surface layer. Various forms of stability parameters are shown to be universallyrelated.
Abstract
The similarity which exists between the stably stratified atmospheric boundary layer and a wind tunnelboundary layer developing over a cold plate is illustrated. It is shown that mean flow and turbulence characteristics in the near wall region of the stratified boundary layer are well described by Monin and Obukhovssimilarity theory, and that this theory provides a good basis for modeling in the laboratory of similar characteristics of the atmospheric surface layer. Various forms of stability parameters are shown to be universallyrelated.
Abstract
By using a simple physical model of the baroclinic convective planetary boundary layer, the similarity functions of the geostrophic drag law are expressed as sums of a barotropic part, dependent only on the stability and boundary layer height parameters, and a baroclinicity dependent part. The latter are predicted to he sinusoidal functions of the angle between surface wind and geostrophic shear, their amplitudes being proportional to the normalized magnitude of geostrophic shear. These drag laws are confirmed by the results of a more sophisticated higher-order closure model, which also predict the magnitude of actual wind shears in the bulk of the mixed layer remaining much smaller than the magnitude of imposed geostrophic shear. The results are shown to be supported by some observations from the recent Wangara and ATFX experiments. The surface cross-isobar angle is predicted to increase toward the equator, a trend well confirmed by observations, but in obvious conflict with the drag laws proposed by others who have ignored the height of the lowest inversion base from their similarity considerations.
Abstract
By using a simple physical model of the baroclinic convective planetary boundary layer, the similarity functions of the geostrophic drag law are expressed as sums of a barotropic part, dependent only on the stability and boundary layer height parameters, and a baroclinicity dependent part. The latter are predicted to he sinusoidal functions of the angle between surface wind and geostrophic shear, their amplitudes being proportional to the normalized magnitude of geostrophic shear. These drag laws are confirmed by the results of a more sophisticated higher-order closure model, which also predict the magnitude of actual wind shears in the bulk of the mixed layer remaining much smaller than the magnitude of imposed geostrophic shear. The results are shown to be supported by some observations from the recent Wangara and ATFX experiments. The surface cross-isobar angle is predicted to increase toward the equator, a trend well confirmed by observations, but in obvious conflict with the drag laws proposed by others who have ignored the height of the lowest inversion base from their similarity considerations.
