A New Model of the Oceanic Evaporation Duct

Abstract

Failure to consider anomalous propagation of microwave radiation in the troposphere may result in erroneous meteorological radar measurements. The most commonly occurring anomalous propagation phenomenon over the ocean is the evaporation duct. The height of this duct is dependent on atmospheric variables and is a major input to microwave propagation prediction models. This evaporation duct height is determined from an evaporation duct model using bulk measurements. Two current evaporation duct models in widespread operational use are examined. We propose and test a new model that addresses deficiencies in these two models. The new model uses recently refined bulk similarity expressions developed for the determination of the ocean surface energy budget in the Tropical Ocean Global Atmosphere Coupled Ocean?Atmosphere Response Experiment. Comparison of these models is made using data collected from a boat off Wallops Island, Virginia, during a range of seasons and weather conditions and from the tidal Potomac River during June and August. Independent evaporation duct height determinations are made using profile measurements from the same boat and are corroborated with fade measurements made with a nearby microwave link whenever possible. The proposed model performs better than the other (operational) models for the cases examined and has advantages of internal consistency.