Near-Surface Land-Atmosphere Coupling

The interaction between the land and atmosphere affects the evolution of both these systems, and requires a proper understanding and then representation of the physical processes involved in order to account for them as a coupled system in weather and climate models. Land-atmosphere interaction begins at a local scale, i.e. surface flux interactions with the atmospheric boundary layer (and free-atmosphere above), with the strength of the near-surface coupling dependent on the relationship between soil moisture and evapotranspiration. For strong coupling, a given change in soil moisture yields a large change in evapotranspiration, while for weak coupling, a given change in soil moisture yields a small change in evapotranspiration. Following an analytical development (ignoring advection), we use observations from surface flux sites to examine the evolution of surface fluxes and the role of soil moisture changes, which is related to the vegetation coverage, canopy conductance, soil hydraulic and thermal properties, and surface-layer turbulence. Vegetated and bare soil surfaces have different coupling mechanisms and are contrasted in the analyses. Subsequent work will examine the interaction of surface fluxes and ABL processes in order to extend this relationship in land-atmosphere coupling to larger scales.