A multi-scale modeling study of the impact of land surface heterogeneity on the convective boundary layer in the U.S. Midwest

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A multi-scale modeling study of the impact of land surface heterogeneity on the convective boundary layer in the U.S. Midwest

Please use this identifier to cite or link to this item: http://hdl.handle.net/10355/10857

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Title: A multi-scale modeling study of the impact of land surface heterogeneity on the convective boundary layer in the U.S. Midwest
Author: Vezhapparambu, Sajith, 1974-
Date: 2011-06-03
Publisher: University of Missouri-Kansas City
Abstract: Rain fed agricultural land is the predominant land cover class in the U.S. Midwest. The interannual and sub-seasonal climate variability of this region are determined by atmospheric oscillations on multiple temporal and spatial scales. The principal factors contributing to the growing season rainfall in the U.S. Midwest include synoptic scale moisture intrusion into the region from the Gulf of Mexico through the Great Plains Low Level Jet (LLJ); passing of meso-scale convective systems, which is influenced by the unique nature of air-mass mixing over the region; and the effect of high vegetation and soil moisture that enhances the lower level moisture flux over the region. This dissertation research investigated the influence of multiple land surface forcings, including agricultural practices, on the summer climate variability of the U.S. Midwest. The significant sub-seasonal moisture oscillations in the region and its interannual variability are also examined. Results indicate that wet years were characterized by predominant synoptic scale moisture intrusions into the region, in contrast to the dry years, which lacked significant moisture oscillations and experienced prolonged dry periods. Differences in crops planted in the region affected the sub-seasonal variability of the Normalized Difference Vegetation Index (NDVI) with significant spatial differentiation. A regional climate model (the Colorado State University Regional Atmospheric Modeling System - RAMS) was employed in this study to evaluate the extent to which realistic surface boundary conditions add value to model simulations of warm season convective systems in the U.S. Midwest. Specifically, the North American Land Data Assimilation System (NLDAS) soil moisture data and satellite-derived leaf area index (LAI) were incorporated into RAMS for the model experiments. The results for the case period of August, 2000 showed that incorporating more realistic land surface data into RAMS improved the model performance by capturing locally forced precipitation and enhanced convective activities for the mid-August, 2000 period. The combined influence of heterogeneous soil moisture and satellite-derived LAI on model simulated convective activity was also clearly depicted in the enhanced spectral power of the moisture flux convergence (MFC) field for periods when rainfall was more likely to be locally forced. Importantly, this study provides new evidence on the influence surface heterogeneity in lower boundary layer forcing, such as soil moisture, on the organization of local scale summer convective systems in the U.S. Midwest. This effect is achieved principally through data into RAMS improved the model performance by capturing locally forced precipitation and enhanced convective activities for the mid-August, 2000 period. The combined influence of heterogeneous soil moisture and satellite-derived LAI on model simulated convective activity was also clearly depicted in the enhanced spectral power of the moisture flux convergence (MFC) field for periods when rainfall was more likely to be locally forced. Importantly, this study provides new evidence on the influence surface heterogeneity in lower boundary layer forcing, such as soil moisture, on the organization of local scale summer convective systems in the U.S. Midwest. This effect is achieved principally through the enhancement of differential heating over the region.
URI: http://hdl.handle.net/10355/10857

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