For many hydrologic and atmospheric dynamic purposes the turbulent surface fluxes of sensible and latent (or evaporative) energy and of momentum must be formulated over areas covering a wide range of spatial scales; these are characteristically the scales of river basins and of the grid sizes for integration in current atmospheric circulation models. The bulk atmospheric boundary layer (ABL) similarity (BAS) approach continues to be one of the very few available formulations to describe turbulent surface fluxes over the range of scales from roughly 1 to 10 km, in terms of average characteristics aloft in the upper reaches of the ABL. The approach is reexamined as it relates to atmospheric stability and surface characteristics under conditions of free convection. Since the largest gradients occur near the surface, first a formulation is proposed for the Monin-Obukhov profile functions for convective conditions that is consistent with the theoretical advances by Kader and Yaglom [1990] and with recent experimental data. This is then combined with a slab representation of the mixed layer to derive the most plausible form of the BAS functions, on the basis of presently available information. Finally, it is illustrated with available experimental data that any alternative formulation of bulk ABL transport, regardless of its appearance, is of necessity equivalent with BAS and that the same original variables are at work.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999RG900013

Aspects of bulk atmospheric boundary layer similarity under free-convective conditions

A higher-order-closure model, which contains equations for turbulence covariances as well as the mean field, was developed and used to investigate the structure of the stably-stratified planetary boundary layer. The calculated surface-layer profiles of wind shear, temperature gradient, and dissipation rate agree well with the 1968 Kansas data. A simulation of the evolution of the nocturnal PBL reproduces fairly accurately some observations from the 1973 Minnesota experiments.

Modeling the planetary boundary layer — Extension to the stable case

The evolution of the boundary layer on day 33 of the Wangara experiment in southeast Australia is calculated with a higher-order-closure turbulence model. This model, which includes equations for the mean field as well as the second moments of the turbulent field, is described in detail. The mean profiles of wind, temperature, and humidity, the profiles of heat and humidity fluxes, the Reynolds stress distributions, and the height of the boundary layer are shown between 10 a.m. and 6 p.m. The results agree well with those from Deardorff's 3-D simulation and take relatively little computer time.

The evolution of a convective planetary boundary layer — A higher-order-closure model study

Numerical modelling results are reported from a pilot study investigating the feasibility of developing a technique for daily soil moisture measurement throughout the world, based on GOES infrared data. A detailed one-dimensional boundary layer-surface-soil model was used in order to determine which physical parameters observable from GOES are most sensitive to soil moisture, and which are most effected by seasonal changes, atmospheric effects and vegetation cover. The results of the sensitivity test show that the mid-morning differential of surface temperature with respect to absorbed solar radiation is optimally sensitive to soil moisture. A case study comparing model results with GOES infrared data confirms the sensitivity of this parameter to soil moisture and also confirms the applicability of the model to predicting area-averaged surface temperature changes. Model measurements of soil moisture are expected to be most accurate for dry or marginal agricultural areas where drought is common. Sources of error, including the advection of clouds, are examined and methods of minimizing error are discussed.

Determining Soil Moisture from Geosynchronous Satellite Infrared Data: A Feasibility Study

The aerodynamic roughness parameter z
0 over inhomogeneous ground surfaces, such as cities, rural towns and so on, is determined by analyzing the wind data at AMeDAS observatories in the Tohoku and Kanto districts of Japan, by making use of Rossby number similarity theory It is found that the aerodynamic roughness parameter is proportional to the average size of the roughness elements A practical method of estimating the aerodynamic roughness parameter over an extensive area with various inhomogeneities is developed In this method, the Digital National Land Information data bank is employed As an example, the roughness parameter distribution around Tsukuba Academic City is presented

Aerodynamic roughness over an inhomogeneous ground surface

It is shown that although Coriolis forces cause large production rates of stress in a convective planetary boundary layer, there is a control mechanism, involving mean wind shear which prevents stress levels from becoming large. Higher-order-closure model calculations are presented which show that the stress profiles are essentially linear, regardless of wind direction, providing the geostrophic wind shear vanishes and the wind speed jump across the capping inversion is negligible. It is shown that it will he very difficult to verify these predicted stress profiles experimentally because of averaging time problems. A simple two-layer model is developed which leads to geostrophic drag and heat transfer expressions in fairly good agreement with Wangara data.

O. R. Coté

Papers

Some Aspects of the Structure of Convective Planetary Boundary Layers