Linkage of an operational mesoscale model to an urban emergency assessment system for prediction of windborne contaminants

The linkage of an operational mesoscale numerical weather prediction model, COAMPS® (Coupled Ocean-Atmosphere Mesoscale Prediction System), to an urban-oriented emergency assessment system, CT-Analyst®, is described. COAMPS is a state-of-the-art, air-sea coupled data assimilation and modeling system currently used by the Department of Defense (DoD) for high-resolution (~3-km), operational mesoscale and tactical-scale forecasts. COAMPS employs sophisticated physical parameterizations, including the WRF Urban Canopy Model and the Los Alamos National Laboratory urban model. CT-Analyst was developed to evaluate airborne Contaminant Transport (CT) threats and to aid in making rapid decisions for complex geometry environments such as cities where current transport and dispersion methods are slow and inaccurate. CT-Analyst was designed for the military prior to 9/11 to incorporate verbal reports, to treat systems with mobile sensors, and to function in realistic situations where the nature, amount, and source location of an airborne contaminant or Chemical, Biological, Radiological (CBR) agent is unknown. CT-Analyst is thus well suited to urban defense, including coastal cities, in the Homeland Security context.

Previous linkage of meteorology (i.e., winds and temperatures) to CT-Analyst was only through ad hoc means for selected case studies in which horizontally-uniform meteorological profiles were provided from COAMPS to CT-Analyst. This current work extends the linkage to provide near-real time COAMPS predictions of winds and temperatures over the urban-scale domain covered by CT-Analyst. CT-Analyst gives greater accuracy and much greater speed than possible with current alternatives because it is based on new principles designed to function in the information-starved situations characterizing the first few minutes of a terrorist or accident scenario where alternate technologies do not. These advantages derive from pre-computed three-dimensional Urban Aerodynamics computations based on high-resolution Large Eddy Simulations (LES) which include solar heating, buoyancy, complete building geometry specification, trees, and impressed wind fluctuations. A few detailed urban aerodynamics simulations are pre-computed for each coverage region when CT-Analyst is installed. These results are then extended to all wind directions, speeds, likely sources and source locations through a new data structure called Dispersion NomografsTM .Using these accurate Nomografs, pre-computed for cities, military bases, industrial complexes and other potential targets well in advance, first responders no longer need to wait for supporting analyses. One limitation of this technique is the lack of spatially and temporally varying input winds. A new algorithm in which the temporally and spatially varying COAMPS “skimming level” flow at the urban canopy top is translated throughout the urban canopy via a transfer function will be described. Results will be presented for selected coastal cities to illustrate the sensitivity of contaminant prediction when real-time COAMPS meteorological fields are used. Emergency response guidance provided by CT-Analyst, including real-time, zero-latency functions such as sensor data fusion, backtracking to an unknown source location, and evacuation route planning will be highlighted.

COAMPS® and CT-Analyst® are registered trademarks of the Naval Research Laboratory. NomografsTM is a trademark of the Naval Research Laboratory.