Long-range sound propagation in the region of the subarctic front

The data of two experiments performed in the northwestern Pacific are presented. The propagation path crosses the northern boundary of the subarctic frontal zone. The influence of the frontal zone on the time structure and intensity of the sound field is studied. This influence most clearly manifests itself in the range dependence of the level of the normalized sound field at frequencies of 63–800 Hz. In the region of crossing the boundary of the frontal zone, a change of 1.5–2 dB in the sound field level is observed with localization in distance. In this region, a pronounced increase in the frequency-independent component of the exponential attenuation is also observed (by 0.015 dB/km for explosion-generated signals received at a depth of 600 m). At depths of 150–800 m, a zone of weak variations of the propagation loss is present in the vertical structure of the sound field at the 100-km part of the path in the region of crossing the front. In the experiment with explosion-generated signals, phenomena that are unrelated to the frontal zone are observed as well, namely, the appearance of reverberation forerunners (prereverberation) on separate parts of the path and the presence of bottom-reflected signals on one of the path fractions with a local bottom rise.