Abstract
Above 45 °N latitude the circulation of the Northeast Pacific Ocean is controlled by the counterclockwise Alaskan Gyre of subarctic water. Due to a greater freshwater influx than evaporation, the water column is characterized by the three distinct layers: 0–100 m depth, cold, low salinity water; 100–200 m, zone of strong salinity gradient (halocline); 200 m and below, gradual changes in temperature and salinity. Roden [J. Geophys. Res. 69, 2899–2914 (1964)] has shown that the middle halocline layer is the site of a complex temperature structure with numerous temperature inversions. These temperature inversions result in the formation of secondary sound channels which our analysis shows are widely distributed. Using a PE prediction model the cutoff frequency of a typical secondary sound channel was determined to be approximately 80 Hz. Since depth excess exists at most locations, energy not trapped in the secondary duct remains in the deep sound channel. Relative loss in the two channels is presented as a ...
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