High-resolution mesoscale models with sophisticated surface and boundary layer parameterization schemes have been used to diagnose evolving microwave refractivity structures in topographically complex coastal settings. Layers having a negative gradient in modified refractivity trap electromagnetic (EM) energy in a wave duct that can extend radar ranges well beyond the horizon. Three dimensional model fields provide insight into spatial variability of radar ducts that can be used to optimized over-water surveillance, communications and navigation.

Ducting occurs within and below sharp vertical discontinuities in temperature and especially water vapor, both of which are sensitive to variations in the underlying SST. In this study we investigate the influence on EM trapping layers of a diurnally evolving SST field developed from a high-resolution analysis of satellite, buoy and ship data. The study takes place over Wallops Island, Virginia during an intensive observational field program (Wallops-2000, Apr/May 2000) where measurements of meteorological data and EM propagation conditions were made by instrumented buoy, boat, helicopter and land-based towers. Sensitivity tests are conducted using a fixed, 12-hourly updated and diurnally evolving SST field to ascertain relationships between SST, surface stability and low-level moisture to coastal and offshore ducting characteristics including the frequency, strength, thickness and height of EM trapping layers.