Near-surface scintillation in a coastal ocean region

摘要

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 C$-n$/$+2$/, were computed from the buoy data and compared with scintillation-derived C$-n$/$+2$/ values. The bulk C$-n$/$+2$/ estimates agreed well with the scintillation measurements in unstable conditions. In stable conditions the bulk C$-n$/$+2$/ estimates were higher than the scintillation data, by up to an order of magnitude on average. This disagreement may be due to the effects of ocean waves in decreasing the vertical temperature and humidity gradients in stable conditions from the assumed Monin-Obukhov similarity theory forms, resulting in bulk C$- n$/$+2$/ values that are too high. The bulk C$-n$/$+2$/ estimates decrease rapidly when the absolute air-sea temperature difference approaches small positive values. These predicted decreases in C$-n$/$+2$/ were not observed in the path-averaged scintillation measurements or in single-point turbulence measurements, demonstrating that bulk models which estimate structure parameters based on mean air-sea differences are not valid when the mean air-sea difference approaches zero. It is believed that obtaining a better understanding of surface wave modification of near- surface atmospheric gradients represents the most promising means toward improving the bulk model.