Estimating the Refractive Index Structure Parameter (Cn2) over the Ocean Using Bulk Methods
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Authors
Frederickson, Paul A.
Davidson, Kenneth L.
Zeisse, Carl R.
Bendall, Charles S.
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2000-10
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Abstract
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 C2 were computed from the buoy data and compared with scintillation-derived C2 n n
values. The bulk C2 estimates agreed well with the scintillation measurements in unstable conditions. In stable n
conditions the bulk C2 estimates became increasingly higher than the scintillation values as the air–sea temperature n
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 C2 values that are too high. The bulk C2 estimates n n
decrease rapidly when the absolute air–sea temperature difference approaches small positive values. These
predicted decreases in C2 were not observed in either the path-averaged scintillation measurements or in single- n
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 C2 model is to obtain a better understanding n
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.
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Article
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Meteorology
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Journal of Applied Meteorology, Volume 39, October 2000, pp. 1770-1783.
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.