GCM grid-scale evaporation from mesoscale modeling

Journal Article · Wed Feb 01 04:00:00 EST 1995 · Journal of Climate

OSTI ID:79389

Lacarrere, P; Noilhan, J ^[1]

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1. Meteo-France, CNRM, Toulouse (France)

Atmospheric general circulation models (GCM) require parameterization of subgrid-scale surface fluxes. Most of the current surface schemes in GCMs assume horizontally homogeneous landscape conditions. However, these assumptions are rarely met in the real world for horizontal scales up to 100 km. Since the level of complexity in a GCM surface description steadily increases, the development of aggregation schemes for relevant parameters needs special calibration. The aim of the present paper is to address the issue of spatial variability in land surface properties from horizontal scales ranging from 10 km (a possible resolution for mesoscale models) to 100 km (the size of a GCM grid box). Many field experiments have been carried out during the last decade to investigate the problem of estimating area-averaged surfaces fluxes over non-homogeneous terrain. From these observations, and from mesoscale modeling, it has been shown that spatial changes in surface characteristics affect the overlying atmosphere and, under certain conditions, may generate mesoscale circulations. The effects of surface inhomogeneities on the atmosphere depend on the horizontal scale of landscape variation. Shuttleworth suggests that for typical length scales less than 10 km, no apparent organization can be observed in the atmospheric boundary layer since turbulent processes average everything out. For this type of boundary layer, at sufficiently large height it is possible to find mean atmospheric conditions approximately in equilibrium with the surface as a whole. Claussen proposed to estimate the areally averaged surface fluxes at the blending height for each land-use category of a grid box (1 km x 1 km), instead of computing the area fluxes from effective surface parameters for the entire area. The same idea was incorporated in a surface scheme for resolving explicitly the subgrid-scale variability in vegetation as a mosaic of vegetation tiles. 42 refs., 14 figs., 5 tabs.

• OSTI ID: 79389
• Journal Information: Journal of Climate, Journal Name: Journal of Climate Journal Issue: 2 Vol. 8; ISSN JLCLEL; ISSN 0894-8755
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
99 GENERAL AND MISCELLANEOUS
AIR-BIOSPHERE INTERACTIONS
CALIBRATION
COMPLEX TERRAIN
GENERAL CIRCULATION MODELS
PARAMETRIC ANALYSIS
RESOLUTION
TOPOGRAPHY