Extended Abstract (220K)8.3
Refractivity in the coastal atmospheric boundary layer
Stephen D. Burk, NRL, Monterey, CA; and T. Haack
Sharp vertical gradients within atmospheric thermodynamic profiles in the boundary layer (BL) can create abrupt changes in the refractivity field, thereby impacting the propagation of electromagnetic (EM) waves. This study uses the Naval Research Laboratory’s Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) to investigate refractive structure (particularly at radio and microwave frequencies) during the period (April-May 2000) of a field experiment at Wallops Island, VA. Measurements taken by groups from DOD laboratories, universities, and elsewhere included low-elevation radar frequency pathloss, meteorological conditions (e.g., from buoys, rocketsondes, helicopter profiles), and radar clutter returns (an extensive description of the field campaign appears in TR-01/132 of the Naval Surface Weapons Division, Dahlgren Division). The “Delmarva” or Tidewater Peninsula along which Wallops Island lies (the Chesapeake Bay to the west and the Atlantic Ocean to the east) contains complex topographic and land surface characteristics, as well as pronounced spatial SST variability, all contributing to complex BL structures (e.g., internal BL’s; sea/land breezes; coastal jets). To explore the COAMPS fidelity in forecasting subtle BL and refractivity variations in this region, we nest COAMPS down to an inner grid mesh having 1 km spacing and utilize high vertical resolution in the first several hundred meters above the surface. During the field experiment, measurements were collected along radials extending SE from the coast at Wallops I. a distance of ~65 km over the Atlantic. Similarity theory permits computation of evaporation duct height (EDH) based on the standard meteorological and oceanographic measurements taken during Wallops 2000. Model forecast EDH values may then be compared with those computed from observations. The nature of the refractivity profile above the surface layer (e.g., subrefractive, standard, superrefractive, trapping) was measured by the rocketsondes and helicopter profiles, including horizontal variations in refractive conditions along the measurement path. The ability of COAMPS to predict the correct refractive structure and its variation along the measurement path will be assessed. Given the difficulty of this forecasting task, model shortcomings are anticipated and will be quantified; the data set will be used to explore and test methods of improving model parameterizations, boundary conditions, etc. Upon completion of such mesoscale model refinements, propagation forecasts using model refractivity fields will be compared with measured propagation factors.
Session 8, Clouds and the Marine Boundary Layer
Friday, 8 August 2003, 9:30 AM-12:10 PM
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