In an effort to evaluate the current state-of-the-art' prognostic capability in a challenging littoral setting, an international collaboration developed between several countries to assess their operational forecasting systems in the context of representing mesoscale variability in the MABL refractivity field. These models include the U.S. Naval Research Laboratory's COAMPS®1, Great Britain's Unified Model (UM), New Zealand's MM5, and Canada's GEM, each run for a seven day period over Wallops Island, Virginia, during which extensive field measurements were collected along radials extending up to ~100 km from shore. The field data include helicopter vertical profiles, hourly surface met tower observations, and surface buoy time-series, along with a boat-mounted transmitter and shore-based receiver measuring propagation pathloss.
Model intercomparisons of the domain-wide ducting characteristics such as duct strength, thickness and base height provides insight into the spatial evolution of the refractive environment over the 7-day period. An evaluation of standard statistical metrics of the predicted refractivity and ducting quantities suggests potential for model forecast system improvements that will have the greatest impact on refractivity. Ample mesoscale features characterized the coastal and offshore ducting resulting from the high-resolution SST analysis and complex topographic sea/land breeze flows in an around the coastal bays and rivers, within rapidly changing large-scale forcing. A detailed investigation of these refractive patterns links them to variations in the vertical distribution of water vapor associated with the myriad of mesoscale forcing mechanisms that contribute to structure in the surface, boundary and entrainment layers. The relative importance of several key forcing mechanisms will be considered at the conference.
1 COAMPS is a registered trademark of the Naval Research Laboratory