Subsurface sound channel and seasonal variation of its characteristics in the mid-latitude of Northwest Pacific

A subsurface sound channel (SSC) can make sound waves propagate a considerable distance without reflection. Due to the lack of a detection method, the SSC has not been fully explored since its discovery. In this paper, a detection method is introduced to detect SSCs from a large quantity of Argo float data in the mid-latitude of the Northwest Pacific. The results show that occurrence of SSCs gradually reaches its peak in spring and subsequently begins to decline until winter. Their depth is influenced by the mixed layer depth and seasonal thermocline, and the thickness is influenced by the seasonal thermocline and mode water. We use the discrete Fourier transform to show that the variations of SSCs have a strong interannual character. However, the characteristics of SSC reach their peak with a time delay due to the combined effects of multiple properties. We analyze these combined effects in detail and calculate the time delay using the cross-correlation function.

Automated summary

This paper introduces a detection method to detect SSCs from a large quantity of Argo float data, and find that the depth of SSCs is influenced by the mixed layer depth and seasonal thermocline, while the thickness is influenced by the seasonal thermocline and mode water. Furthermore, the variations of SSCs are found to have strong interannual character using the discrete Fourier transform, but the peak characteristics of SSCs have a time delay due to the combined effects of multiple properties. The combined effects are analyzed in detail and the time delay is calculated using the cross-correlation function.