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.

中文翻译：

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北太平洋上层海洋声速结构的观测及其对中低频中远距离声传播的影响

分析了由船舶牵引的车辆SeaSoar在北太平洋获得的三个1000公里长的高分辨率电导率，温度，深度剖面，以量化2005年3月/ 4月上层海洋的声速结构，并确定了对中低层的影响。通过数值模拟得出频率传输损耗（TL）。观察结果表明，可变混合层声波导管（MLAD）的平均声波层深度为91-m，并且具有更高的可变性，平均厚度为80-m的过渡层将混合层（ML）与主温跃层相连。假设声速结构与热盐过程有关，例如海气通量，涡流，亚中尺度，前沿，内波，湍流和香料，但分析并未隔离这些因素。使用层深度，ML梯度和声速的可观测值来量化大洋变化，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。使用附加到气候学的上部400-m处的声速观测结果，进行了400和1000 Hz的耦合模式声传播模拟，揭示了与衍射，随机介质效应和确定性特征散射有关的传播物理学。TL的统计数据揭示了MLAD和深声道之间的重要能量转移。使用附加到气候学的上部400-m处的声速观测结果，进行了400和1000 Hz的耦合模式声传播模拟，揭示了与衍射，随机介质效应和确定性特征散射有关的传播物理学。TL的统计数据揭示了MLAD和深声道之间的重要能量转移。使用附加到气候学的上部400-m处的声速观测结果，进行了400和1000 Hz的耦合模式声传播模拟，揭示了与衍射，随机介质效应和确定性特征散射有关的传播物理学。TL的统计数据揭示了MLAD和深声道之间的重要能量转移。