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