Abstract
As part of the preparation for the Large-Scale Biosphere Atmosphere Experiment in Amazonia, a meso-scale modelling study was executed to highlight deficiencies in the current understanding of land surface atmosphere interaction at local to sub-continental scales in the dry season. Meso-scale models were run in 1-D and 3-D mode for the area of Rondonia State, Brazil. The important conclusions are that without calibration it is difficult to model the energy partitioning of pasture; modelling that of forest is easier due to the absence of a strong moisture deficit signal. The simulation of the boundary layer above forest is good, above deforested areas (pasture) poor. The models' underestimate of the temperature of the boundary layer is likely to be caused by the neglect of the radiative effects of aerosols caused by biomass burning, but other factors such as lack of sufficient entrainment in the model at the mixed layer top may also contribute. The Andes generate patterns of subsidence and gravity waves, the effects of which are felt far into the Rondonian area The results show that the picture presented by GCM modelling studies may need to be balanced by an increased understanding of what happens at the meso-scale. The results are used to identify key measurements for the LBA atmospheric meso-scale campaign needed to improve the model simulations. Similar modelling studies are proposed for the wet season in Rondonia, when convection plays a major role.Key words. Atmospheric composition and structure (aerosols and particles; biosphere-atmosphere interactions) · Meterology and atmospheric dynamics (mesoscale meterology)
Highlights
Modelling studies with general circulation models have shown that large-scale deforestation of the Amazon basin may result in increased surface temperatures and decreased rainfall (e.g. Lean and Rowntree, 1993)
Experiments with meso-scale models have shown that increased heating of the boundary layer may trigger convection, if the initial moisture availability is suciently large (Avissar and Liu, 1996)
As deforestation does not aect the whole of the Amazon basin as yet, but is concentrated in regions such as Rondonia or Para, there is a clear need to understand the interplay between the micro, meso, and macro-scale processes, with regard to rainfall generation
Summary
Modelling studies with general circulation models have shown that large-scale deforestation of the Amazon basin may result in increased surface temperatures and decreased rainfall (e.g. Lean and Rowntree, 1993). Modelling studies with general circulation models have shown that large-scale deforestation of the Amazon basin may result in increased surface temperatures and decreased rainfall As the boundary layer plays a key role as mediator between the surface and large-scale weather systems, it is of obvious importance to correctly model and understand the mechanisms involved in the boundary layer growth of the Amazonian dry season. This is even more so, as the drying predicted by GCMs will have the strongest ecological implications during the dry season, when rainfall is scarce, and most probably of local origin (Cutrim et al, 1995).
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