SUMMARY

Between 0.1 and 0.5 Hz, infrasound signals recorded in the atmosphere are dominated by ocean-generated noise called microbaroms. Microbaroms propagate through the atmosphere over thousands of kilometres due to low absorption and efficient ducting between the ground and the stratopause. Different theoretical models have been developed to characterize the source of microbaroms, all based on the second-order nonlinear interaction of ocean waves. While early theories considered an infinite ocean depth and a source radiation depending on the acoustic wave elevation angle, other works have approximated the radiation pattern as a monopole, and found a considerable effect of the water depth. This paper reviews these models and extends the previous theories to the combined effects of both finite depth ocean and source directivity in both elevation and azimuth angles. It is found that the water depth has a negligible effect for the near-horizontally propagating acoustic waves that should dominate the measured microbarom records. Another important result is that the microbarom azimuthal variation can be highly directive locally, but it generally becomes isotropic when integrated over a realistic source region.

中文翻译：

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海浪在有限深度下产生大气次声：统一理论及其在辐射方向图上的应用

概要

在0.1到0.5 Hz之间，记录在大气中的次声信号主要由海洋产生的称为微气压的噪声控制。由于低吸收和地面与层间绝顶之间的有效导管，微气压虫在大气中传播了数千公里。已经开发了不同的理论模型来表征微气压源，所有这些模型都是基于海浪的二次非线性相互作用。早期的理论认为无限深的海洋和取决于声波仰角的源辐射，其他工作已将辐射方向图近似为单极子，并发现了水深的显着影响。本文回顾了这些模型，并将先前的理论扩展到有限深度海洋和源指向性在仰角和方位角上的组合作用。发现水深对于应在所测微气压记录中占主导地位的近水平传播声波影响可忽略不计。另一个重要的结果是，微气压传感器的方位角变化在局部可以是高度定向的，但是当集成在实际的源区域上时，它通常变为各向同性的。