The release of chemical/biological (CB) agents or other toxic materials in an urban area - whether from an industrial accident or terrorist act - represents a real threat to large populations. A central issue for emergency planning, warning and mitigation purposes is to understand how CB agents are physically transported in the urban boundary layer. Mesoscale processes on a scale of 1 to 100 km resulting from boundary layer heating, terrain forcing, and turbulent mixing are expected to play a critical role in the spread of CB agents near the surface. We are utilizing mesoscale numerical models and field observation platforms to simulate the transport and dispersion of CB agents in the boundary layer. Two key requirements for a suitable mesoscale prediction system will be nested grid capability for multi-scale simulation and an advanced treatment of boundary layer physics. Two key scientific questions to be considered by this project are (a) What are the characteristic features of urban boundary layer processes and their relationships to surface flow? and (b) Will invoking Mesonet data significantly improve the boundary layer initialization of mesoscale models, and consequently the model performance? We will address these questions via real-data model simulation experiments and comprehensive post-forecast verification and diagnostics.

A variety of field observation platforms at Texas Tech University will be used in conjunction with the modeling effort. The West Texas Mesonet, including thirty-two surface data collection sites at a spatial resolution of approximately 50-km, is being established and will provide useful field data. Three of these sites will include atmospheric profilers capable of providing wind and stability measurements of the lowest several kilometers of the atmosphere. Specially-designed mobile and portable surface layer platforms are developed for gathering remote measurements of atmospheric conditions under otherwise potentially hazardous circumstances. These platforms are used to establish the horizontal and vertical scales of turbulence, growth of inner boundary layers, and the diurnal evolution of boundary layer winds. These facilities allow creation of detailed three-dimensional representations of boundary-layer wind fields and will provide the basis for improving our understanding of the transport of hazardous airborne contaminants, including chemical and biological agents. The field data are used both to initialize the numerical mesoscale simulations, and to validate the output from these model runs.