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A High-Resolution Model of the Planetary Boundary Layer—Sensitivity Tests and Comparisons with SESAME-79 Data

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  • a Department of Meteorology, The Pennsylvania State University, University Park 16802
  • | b National Center for Atmospheric Research, Boulder, CO 80307
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Abstract

A high-resolution, one-dimensional, moist planetary boundary layer (PBL) model is developed following Blackadar, and verified using the 10 April 1979 SESAME data set. The model consists of two modules to predict the time-dependent behavior of the PBL under various surface characteristics. Under stable conditions, turbulent fluxes are related to a local Richardson number. In contrast, under conditions of free convection, the exchange of heat, moisture and momentum occurs through mixing between convective elements originating at the surface and environmental air in the PBL.

Sensitivity tests showed that the daytime PBL structure is most sensitive to moisture availability, roughness length, albedo and thermal capacity, in that order. It is less sensitive in the nighttime to the above parameters. The wind profile is extremely sensitive to the specified geostrophic wind profile at all times. Simulations over both dry and moist terrain indicate that both the free convection (daytime) and the stable (nocturnal) modules are capable of accurately simulating the diurnal PBL evolution under nonsteady geostrophic conditions, provided accurate, time-dependent geostrophic wind profiles are available. With steady geostrophic forcing, the simulations are less realistic.

Abstract

A high-resolution, one-dimensional, moist planetary boundary layer (PBL) model is developed following Blackadar, and verified using the 10 April 1979 SESAME data set. The model consists of two modules to predict the time-dependent behavior of the PBL under various surface characteristics. Under stable conditions, turbulent fluxes are related to a local Richardson number. In contrast, under conditions of free convection, the exchange of heat, moisture and momentum occurs through mixing between convective elements originating at the surface and environmental air in the PBL.

Sensitivity tests showed that the daytime PBL structure is most sensitive to moisture availability, roughness length, albedo and thermal capacity, in that order. It is less sensitive in the nighttime to the above parameters. The wind profile is extremely sensitive to the specified geostrophic wind profile at all times. Simulations over both dry and moist terrain indicate that both the free convection (daytime) and the stable (nocturnal) modules are capable of accurately simulating the diurnal PBL evolution under nonsteady geostrophic conditions, provided accurate, time-dependent geostrophic wind profiles are available. With steady geostrophic forcing, the simulations are less realistic.

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