The IAGL Land Surface Model

Abstract

A model that computes the fluxes of energy and momentum between the land surface and the atmosphere is presented. It is designed to serve as a lower boundary in a mesoscale atmospheric model and is intended to be used to study the influence of the land surface on regional atmospheric circulations and climate. The land surface model contains one vegetation layer, a soil skin layer, and four subsurface soil layers. The shortwave and longwave radiation schemes are based on the two-stream theory. Turbulent transfer is treated in a very simple manner, by considering canopy?air and ground?air exchanges separately. Plant water flow is governed by differences in water potential between the soil and the leaves. The stomatal resistance formulation uses the effective leaf area index and the leaf water potential as key variables. It is shown that the resulting transpiration scheme implicitly accounts for the influence of visible radiation, soil moisture, atmospheric saturation deficit, and leaf temperature. The results of four validation experiments are shown. Parameters were chosen prior to the model runs, and no tuning was involved. These experiments show that the surface model is capable of reproducing observed fluxes within instrumental error including timescales ranging from rapid weather changes up to several months.