The Impact of Spatial and Temporal Variability of the Landscape on Atmosphere-Land Surface Interactions at the Mesoscale

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9415441 Avissar As part of a prior NSF investigation (EAR-9105059), it was demonstrated that subgrid-scale heat and momentum fluxes associated with mesoscale circulations generated by horizontal gradients of water availability for evapotranspiration, have a significant impact on the atmospheric processes simulated with large-scale atmospheric numerical models (e.g., GCMs). However, these fluxes, which can be three times stronger than turbulent (i.e., microscale) fluxes, are not represented in such models. The research proposed here is a continuation of this prior investigation, which concentrates on clouds and precipitation generated by landscape discontinuities at the mesoscale and their interactions with the horizontal distribution of soil moisture, evapotranspiration, and the other surface fluxes. The proposed research includes three major tasks, which are expected to be accomplished within three years (one task a year): (i) a sensitivity analysis of which parameters are most important in the parameterization of cloud and precipitation microphysics relevant to land-atmosphere interactions; (ii) a systematic analysis of the impact of water availability for evapotranspiration at the ground surface on clouds and precipitation; and (iii) a parameterization of mesocale heart fluxes (including moist processes) generated by land-surface heterogeneity for large-scale atmospheric models. To perform efficiently this research, which is based on numerical analysis, it is very important to adopt a models that has refined parameterizations of cloud physics as well as land hydrology. Furthermore, it should have the flexibility to produce simulations on a broad range of spatial scales. Thus, the Colorado State University (CSU) Regional Atmospheric Modeling System (RAMS), a state-of-the-art modeling system designed to support basic research in the atmospheric sciences will be used for this investigation. This research, which will provide new insights in the complex hydrometeorological processes in volved in land-atmosphere interactions at the mesoscale, is expected to be particularly relevant and beneficial for the research activity endorsed by GEWEX and other national and international programs.