The research will initially focus on completing studies begun in FY99, that are analyzing previous observations taken in stable conditions from field programs in New Mexico near Los Alamos and in El Paso. These studies are focusing primarily on understanding stable layer formation in El Paso under various large-scale weather regimes and in quantifying urban heat and roughness effects with data analysis and RAMS modeling. In addition, with the Los Alamos area data set, we are examining stable terrain-induced flow layering and convergence and mixing from a mountain canyon into a valley with data analysis and RAMS/HYPACT modeling. The model simulations will try to recreate the observed flow behavior within stable boundary layers. These simulations will provide three-dimensional, physically-consistent fields with greater detail than possible from measurements and simulated particle tracer transport within the simulated SBLs. We will then investigate data from CASES or other flat terrain experiments comparing and contrasting analyses of the SBL from flat topography with the SBL in complex terrain (Los Alamos, El Paso) to determine, in a gross sense, the influence of topography and urban areas on mixing and transport.
Before the start of the Salt Lake City field campaign, we intend to conduct preliminary numerical modeling investigations of the Salt Lake City region with the RAMS model. These simulations will investigate several case study days based upon a brief climatological analysis, to identify key regions for instrument placement, types of instrumentation necessary to observe phenomena of interest, and to develop a conceptual model of what dominant mixing and transport processes can be anticipated.
Data analysis after the experiment will examine a double transect of vertical profiling and ancillary ground station measurements. The two transects will provide data on cross-basin mixing due to side canyon influences, and also along-basin influences due to the urban canopy. We intend to use these data to observe the 3-D behavior of flow merger and layering. We will also analyze an along-basin transect to look specifically at the effects of the heat and roughness of the urban center on the vertical structure and compare this with rural soundings.
Idealized modeling and case study simulations of the VTMX-2000 experiment will be designed to isolate the effect of specific mixing processes due to the merger of complex terrain flows over specific regions of the basin, due to synoptic influences, and due to the heat and roughness induced by the urban canopy. In these simulations, we plan to use both the RAMS mesoscale model down to sub-kilometer resolution and the HIgh resolution and strong GRADient applications (HIGRAD) model at ~10-50 m resolution to examine the details of stable flow interactions. In simulating at high resolution the flow behavior that leads to mixing in stable boundary layers, we will quantify the relative importance of specific flow types for vertical transport and mixing. Particle releases within RAMS and HIGRAD will be used to investigate the transport of material through these complex interaction zones. We hope to compare the particle transport modeling results with VTMX-2000 tracer experiment data to investigate the local-scale to meso-scale fate of pollutants from point (canyon) or area (urban region) sources. Both idealized boundary conditions for sensitivity testing and assimilated boundary conditions for HIGRAD from RAMS case day simulations will be considered. The RAMS/HIGRAD combined modeling effort will also allow us to quantify the limitations of a mesoscale model (RAMS) in simulating microscale mixing (more explicitly simulated by HIGRAD) through the sub-grid turbulence parameterization.
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