Parameterization of Surface Moisture and Evaporation Rate in a Planetary Boundary Layer Model

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Abstract
Two methods of pararmeterizing expressions for ground surface evaporation rate that are used in planetary boundary layer models have been examined. In one method (Method A) the surface evaporation rate is proportional to M (Qs − Q1). In the other (Method B) the surface evaporation rate is proportional to hQs − Q1. Here Qs is the surface saturation mixing ratio, Q1 the mixing ratio at the lowest level of the atmospheric model, M the moisture availability parameter, and h the relative humidity immediately above the ground. The analysis was performed by running a planetary boundary layer numerical model several times, using at each time either Method A or B with different specifications of M and h. The calculated diurnal surface temperature and surface latent heat flux were examined. Specific results are: 1) for equal M andh, Method B results in higher surface temperatures than Method A; 2) the surface evaporation rate calculated using Method A is less sensitive to changes in M, than the surface eva... Abstract Two methods of pararmeterizing expressions for ground surface evaporation rate that are used in planetary boundary layer models have been examined. In one method (Method A) the surface evaporation rate is proportional to M (Qs − Q1). In the other (Method B) the surface evaporation rate is proportional to hQs − Q1. Here Qs is the surface saturation mixing ratio, Q1 the mixing ratio at the lowest level of the atmospheric model, M the moisture availability parameter, and h the relative humidity immediately above the ground. The analysis was performed by running a planetary boundary layer numerical model several times, using at each time either Method A or B with different specifications of M and h. The calculated diurnal surface temperature and surface latent heat flux were examined. Specific results are: 1) for equal M andh, Method B results in higher surface temperatures than Method A; 2) the surface evaporation rate calculated using Method A is less sensitive to changes in M, than the surface eva...

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