Infrared scintillation measurements were obtained along a 7-km path over San Diego Bay concurrently with meteorological measurements obtained from a buoy at the midpoint of the path. Bulk estimates of the refractive index structure parameter were computed from the buoy data and compared with scintillation-derived values. The bulk estimates agreed well with the scintillation measurements in unstable conditions. In stable conditions the bulk estimates became increasingly higher than the scintillation values as the air–sea temperature difference increased. This disagreement may be due to enhanced wave-induced mixing of the lower atmosphere that decreases the vertical temperature and humidity gradients in stable conditions from the assumed Monin–Obukhov similarity (MOS) theory forms, resulting in bulk values that are too high. The bulk estimates decrease rapidly when the absolute air–sea temperature difference approaches small positive values. These predicted decreases in were not observed in either the path-averaged scintillation measurements or in single-point turbulence measurements, indicating that bulk models for estimating scalar structure parameters based on mean air–sea scalar differences are not valid when the mean air–sea difference approaches zero. The authors believe that the most promising means toward improving the bulk model is to obtain a better understanding of the MOS functions over the ocean for a wide stability range, and particularly of the role of ocean waves in modifying near-surface vertical gradients and turbulence characteristics.
The Rough Evaporation Duct experiment aimed to see if the effects of ocean waves account for errors in modeling the ranges at which radar and infrared can detect low-flying targets. When radars first came into operation during the late 1930s, they were not expected to detect targets much beyond the geometrical horizon. These early radars, operating at a wavelength of 13 m, generally met expectations. As new radars were rapidly developed, operating at shorter and shorter wavelengths for better target detection, observations of anomalous propagation effects became more frequent. When 10-cm radars were installed along the south coast of England during World War II, they were often able to see the coast of France, even though the coast was well beyond the geometric horizon (Booker 1948). These anomalous propagation effects also became more pronounced as the operating area became more tropical. For example, a 1.5-mwavelength radar operating in Bombay, India, re-
This study surveys and evaluates similarity theory for estimating the sea‐surface drag coefficient with the bulk aerodynamic method. The most commonly used formulations of the aerodynamic roughness length, required by similarity theory, are examined using data sets from four different field programs. These relationships include the Charnock formulation and the wave age modified Charnock relationship. The goal is to assess the overall performance of simple formulations of the roughness length including cases where the Charnock formulation is not expected to apply, and to assess the errors resulting from application of the Charnock formulation to all conditions, as is done in many numerical models where an explicit wave model cannot be accommodated. This examination indicates that spurious self‐correlation explains more variance than actual physical relationships, even after eliminating weak wind cases. Frequent cases of anomalously low stress and very small values of the Charnock coefficient further reduce the usefulness of this formulation for the present data sets. Causes of the frequent very small values of the Charnock coefficient are briefly investigated.
In this study, offshore flow will be examined in terms of eddy correlation aircraft data collected approximately 15 m above the sea surface (section 3). In the next section we review the basic formulations required for the analysis in sections 4-7, using the data described in section 3. Existing Parameterization of the Surface StressThe drag coefficient is computed aswhere u, is the friction velocity based on averaged components of the stress vector and U is the wind speed computed from 20,629
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