The Impact on a GCM Climate of an Extended Mosaic Technique for the Land-Atmosphere Coupling


Heterogeneities in the land surface on scales smaller than the typical General Circulation Model (GCM) grid size can have a profound influence on the grid scale mean climate. There exists observational and modeling evidence that the surface heterogeneities are felt by the atmosphere up to some level above the ground. The impact of including an `Extended Mosaic' (EM) scheme which accounts for the vertical influence of land surface heterogeneities in a GCM is evaluated here by comparing side by side GCM simulations with EM and the more standard Mosaic formulation (M).

Differences between the EM and M simulations are observed in the boundary layer structure, in fields which link the boundary layer and the general circulation, and in the general circulation itself. Large EM-M differences are found over the eastern U.S., eastern Asia and southern Africa in the summertime, and are associated with a boundary layer eddy diffusion feedback mechanism. The feedback mechanism operates as a positive or negative feedback depending on the local Bowen ratio. Significant EM-M differences are also found in the region of the Australian monsoon, and in the strength of the stationary PNA pattern in the northern Pacific.

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