Intensity Fluctuation and Depth Dependence in Acoustic Experiment of Yellow Sea Front and Internal Waves

Abstract

Nonlinear internal waves (NIWs) passing through the vertical line array and induced acoustic fluctuation were observed in AEYFI2005 (Acoustic Experiment of Yellow Sea Oceanic Front and Internal Wave in 2005). In this paper, we present analysis of the peak fluctuation of the wideband signal recorded by the vertical line array which is deployed at 37 km away from the source, and the antinode fluctuation of the depth function of the 1st normal mode induced by NIWs. Although there exists no significant mode coupling, the peak-to-peak variation of signal amplitude larger than 6dB is observed. Simultaneously, it is found that the antinode fluctuation of the depth function of the 1st normal mode extracted using the data-derived method is good in agreement with the fluctuation of thermocline measured by the thermistor chain. We explain these experimental results by using numerical simulations and theoretical analysis. It turns out that these can be interpreted as acoustic fluctuation due to the variation of local depth function of normal modes induced by NIWs.