Abstract
Four cases of an overlying inversion imposed on a stable boundary layer are investigated, extending the earlier work of Hancock and Hayden (Boundary-Layer Meteorol 168:29–57, 2018), where no inversion was imposed. The inversion is imposed to one or other of two depths within the layer: midway or deep. Four cases of changed surface condition are also investigated, and it is seen that the surface and imposed conditions behave independently. A change of imposed inversion condition leaves the bottom 1/3 of the layer almost completely unaffected; a change of the surface condition leaves the top 2/3 unaffected. Comparisons are made against two sets of local-scaling systems over the full height of the boundary layer. Both show some influence of the inversion condition. The surface heat flux and the reduction in surface shear stress, and hence the ratio of the boundary-layer height to surface Obukhov length, are determined by the temperature difference across the surface layer (not the whole layer), bringing all cases together in single correlations as functions of a surface-layer bulk Richardson number.
Highlights
A stable atmospheric boundary is a naturally occurring phenomenon, for example, arising after the cessation of daytime convective motions
The working-section inlet temperature, ΘIN(z), for cases 3–6 is shown in the profiles of Fig. 1a, together with the profile for no inversion, case 2, this latter case corresponding to the ‘final case’ example given in Hancock and Hayden (2018); Θ0 is the surface temperature
As a summary characteristic this demarcation has been inferred from a variety of upstream conditions: no-inversion, two inversion depths, a range of inversion gradients, a range of near-surface temperature difference
Summary
A stable atmospheric boundary is a naturally occurring phenomenon, for example, arising after the cessation of daytime convective motions. Hancock and Hayden (2018) deliberately did not impose an inversion They found that the temperature profile at the windtunnel working-section inlet must be non-uniform, i.e. increasing with height, over the depth of the boundary layer if the whole depth of the layer is to be stably stratified. A uniform inlet temperature (above that of the surface) led to about the top third of the layer remaining neutral, the bottom third being stable, and the middle third being an adjustment region Turbulence quantities such as Reynolds stresses could vary non-monotonically with height. The overall objective is the extension of the simulation technique presented in Hancock and Hayden (2018) to the case where there is an overlying inversion, and such that the Reynolds stresses decrease smoothly to a low turbulence level above the top of the boundary layer. Hancock and Hayden (2018) has been extended to that of rougher surfaces for studies of the urban environment (Marucci et al 2018) in stable boundary layers
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