Keywords

aggregation of surface parameters, albedo, modelling

Start Date

1-7-2002 12:00 AM

Description

In the atmospheric models, the underlying surface consists of patches of solid and liquid parts and different plant communities, creating very heterogeneous picture in the grid-cell. In those cases, numerical modelers usually make a simple average to determine albedo as the grid-cell average albedo, a key variable in the parameterization of the land-surface radiative transfer over it. This method leads to uncertainties in the parameterization of the boundary layer processes when heterogeneities exist over the grid-cell. Also, a physics-based analysis indicates that there is a significant departure of the albedo above such a heterogeneous surface from that calculated by simple averaging, seriously affecting the calculated values of momentum, heat and water vapour transfer from the surface fluxes into the atmosphere. The object of this paper is to consider the assumptions for aggregating the albedo over a very heterogeneous surface, and, then propose a method for evaluating a general expression for it. The suggested expression for the albedo is compared with the conventional approach, using a common parameterization of albedo over the grid-cell, and the two-patches grid-cell with a simple geometrical distribution and different heights of its components.

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Jul 1st, 12:00 AM

An Approach for the Aggregation of Albedo in Calculating the Radiative Fluxes over Heterogeneous Surfaces in Atmospheric Models

In the atmospheric models, the underlying surface consists of patches of solid and liquid parts and different plant communities, creating very heterogeneous picture in the grid-cell. In those cases, numerical modelers usually make a simple average to determine albedo as the grid-cell average albedo, a key variable in the parameterization of the land-surface radiative transfer over it. This method leads to uncertainties in the parameterization of the boundary layer processes when heterogeneities exist over the grid-cell. Also, a physics-based analysis indicates that there is a significant departure of the albedo above such a heterogeneous surface from that calculated by simple averaging, seriously affecting the calculated values of momentum, heat and water vapour transfer from the surface fluxes into the atmosphere. The object of this paper is to consider the assumptions for aggregating the albedo over a very heterogeneous surface, and, then propose a method for evaluating a general expression for it. The suggested expression for the albedo is compared with the conventional approach, using a common parameterization of albedo over the grid-cell, and the two-patches grid-cell with a simple geometrical distribution and different heights of its components.