Colosi John A, Rudnick Daniel L
Department of Oceanography, Naval Postgraduate School, Monterey, California 93943, USA.
Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093, USA.
J Acoust Soc Am. 2020 Oct;148(4):2040. doi: 10.1121/10.0002174.
Three 1000-km long, high resolution conductivity, temperature, depth sections in the North Pacific Ocean obtained by the ship towed vehicle SeaSoar are analyzed to quantify 2005 March/April upper-ocean sound-speed structure and determine the effects on low to mid-frequency transmission loss (TL) through numerical simulation. The observations reveal a variable mixed layer acoustic duct (MLAD) with a mean sonic layer depth of 91-m, and an even higher variability, 80-m-average-thickness transition layer connecting the mixed layer (ML) with the main thermocline. The sound-speed structure is hypothesized to be associated with thermohaline processes such as air-sea fluxes, eddies, submesoscale, fronts, internal waves, turbulence, and spice, but the analysis does not isolate these factors. Upper-ocean variability is quantified using observables of layer depth, ML gradient, and sound speed to compute low order moments, probability density functions, horizontal wavenumber spectra, and empirical orthogonal function decomposition. Coupled mode acoustic propagation simulations at 400 and 1000 Hz were carried out using the sound-speed observations from the upper 400-m appended to climatology, which reveal propagation physics associated with diffraction, random media effects, and deterministic feature scattering. Statistics of TL reveal important energy transfers between the MLAD and the deep sound channel.
对通过船拖式车辆“海洋翱翔者”（SeaSoar）在北太平洋获取的三段1000公里长的高分辨率电导率、温度、深度剖面进行了分析，以量化2005年3月/4月上层海洋声速结构，并通过数值模拟确定其对低频至中频传输损耗（TL）的影响。观测结果揭示了一个可变的混合层声导管（MLAD），其平均声层深度为91米，以及一个连接混合层（ML）和主温跃层的平均厚度为80米的更高变率过渡层。假设声速结构与诸如海气通量、涡旋、亚中尺度、锋面、内波、湍流和香料等热盐过程有关，但分析并未分离出这些因素。利用层深度、ML梯度和声速的可观测量对上层海洋变率进行量化，以计算低阶矩、概率密度函数、水平波数谱和经验正交函数分解。利用上层400米的声速观测结果并附加气候学数据，进行了400赫兹和1000赫兹的耦合模声传播模拟，揭示了与衍射、随机介质效应和确定性特征散射相关的传播物理。TL统计揭示了MLAD和深层声道之间重要的能量转移。
