Testing of Several Recent Modifications to Arps Land Surface Model

1. INTRODUCTION Deardorff (1978, D78 henceforth) showed that a two-layered force-restore scheme is superior to bulk scheme in describing the surface soil moisture content because it contains the mechanism by which a deeper soil layer can influence the thin surface layer. This gives the flexibility and advantages in superficial soil moisture prediction especially when there are precipitation and very active evaporation from the ground surface. Further, an accurate estimation of surface latent heat flux resulting from the use of surface layer moisture content rather than that of the thick, slow responding bulk layer is very important for the prediction of surface air temperature and humidity. Another significant contribution of Deardorff (1977, D77 hereafter) and D78 is the inclusion of a vegetation layer in the description of the land surface processes. Without proper consideration of the shielding effects and the transpiration of the root zone soil moisture, force-restore temperature and moisture schemes can only be applied to bare ground for reasonably good results. With his approach, the vegetated surface is conceptually divided into bare ground and the portion covered by vegetation. Energy balance for vegetation was derived that includes the diagnosis of canopy temperature, the parameteri-zation of a representative leave for its potential evapotranspiration rate, and the fractional exponent description of dew formation and evaporation. He used the concept of canopy surface resistance originated by Monteith (1965) and implemented the daylight , soil moisture and seasonal dependence of the stomatal resistance. The representative leaf-to-canopy scaling is connected by the leaf area index through a linear proportionality. Land surface models inspired by Deardorff's philosophy of explicitly describing the land surface processes include Biosphere Atmosphere Transfer Scheme (BATS, Dickinson 1984) and the Simple Biosphere Model (SiB, Sellers et al. 1986), among others, for different specific purposes. Contrary to the approach that makes the parameteri-zation and the description of the physical processes more detailed and complex, the Interactions Soil Bio-sphere Atmosphere (ISBA) by Noilhan and Planton (1989, NP89 henceforth) is a relatively simple scheme that includes only the most important components of the land surface processes. Because its relative efficiency and suitability for mesoscale modeling applications, ISBA has been actively tested and improved by many researchers, among them are the improvement in heat capacity description by Pleim and Xiu (1995), the continuous formulation for the secondary soil parameters by Noilhan and Mahfouf (1996, NM96 henceforth), re-calibration of the force-coefficient for surface soil moisture by …