AN ANALYTIC APPROACH TO MODELING LAND ATMOSPHERE INTERACTION .1. CONSTRUCT AND EQUILIBRIUM BEHAVIOR

A four-variable land-atmosphere model is developed to investigate the coupled exchanges of water and energy between the land surface and atm osphere and the role of these exchanges in the statistical behavior of continental climates. The land-atmosphere system is substantially sim plified and formulated as a set of ordinary differential equations tha t, with the addition of random noise, are suitable for analysis in the form of the multivariate Ito equation. The model treats the soil laye r and the near-surface atmosphere as reservoirs with storage capacitie s for heat and water. The transfers between these reservoirs are regul ated by four states: soil saturation, soil temperature, air specific h umidity, and air potential temperature. The atmospheric reservoir is t reated as a turbulently mixed boundary layer of fixed depth. Heat and moisture advection, precipitation, and layer-top air entrainment are p arameterized. The system is forced externally by solar radiation and t he lateral advection of air and water mass. The remaining energy and w ater mass exchanges are expressed in terms of the state variables. The model development and equilibrium solutions are presented. Although c omparisons between observed data and steady state model results are in exact, the model appears to do a reasonable job of partitioning net ra diation into sensible and latent heat flux in appropriate proportions for bare-soil midlatitude summer conditions. Subsequent work will intr oduce randomness into the forcing terms to investigate the effect of w ater-energy coupling and land-atmosphere interaction on variability an d persistence in the climatic system.