Title: Induced Diffusion of Internal Gravity Waves: Directionality and Role in Ocean Mixing Show Chinese title

Title: 惯性重力波的诱导扩散：方向性及其在海洋混合中的作用

Abstract: Induced diffusion (ID), an important mechanism of spectral energy transfer in the internal gravity wave (IGW) field, plays a significant role in driving turbulent dissipation in the ocean interior. In this study, we revisit the ID mechanism to elucidate its directionality and role in ocean mixing under varying IGW spectral forms, with particular attention to deviations from the standard Garrett-Munk (GM) spectrum. The original interpretation of ID as an action diffusion process, as proposed by McComas et al., suggests that ID is inherently bidirectional, with its direction governed by the vertical-wavenumber spectral slope $\sigma$ of the IGW action spectrum, $n \propto m^\sigma$. In contrast, by evaluating the wave kinetic equation, we reveal a more complete depiction of ID, comprising both diffusive and scale-separated transfers that are rooted in energy conservation within wave triads. Although the action diffusion may reverse direction depending on the sign of $\sigma$ (i.e., between red and blue spectral cases), the combined ID transfer consistently leads to a forward energy cascade at the dissipation scale, thereby contributing positively to turbulent dissipation. This supports the viewpoint of ID as a dissipative mechanism in physical oceanography. This study presents a physically grounded overview of ID and offers insights into the specific types of wave-wave interactions responsible for turbulent dissipation. Show Chinese abstract

Abstract: 诱导扩散（ID）是内波场中谱能量传输的一个重要机制，在驱动海洋内部湍流耗散中起着重要作用。 本研究重新审视了ID机制，以阐明其方向性和在不同内波谱形式下对海洋混合的作用，特别关注偏离标准Garrett-Munk（GM）谱的情况。 McComas等人最初将ID解释为一种作用扩散过程，表明ID本质上是双向的，其方向由内波作用谱的垂直波数谱斜率 $\sigma$ 决定，记作 $n \propto m^\sigma$。 相比之下，通过评估波动能方程，我们揭示了ID的一个更完整的描述，包括源自波三重相互作用内能守恒的扩散和尺度分离转移。 尽管作用扩散可能因 $\sigma$ 的符号（即红谱与蓝谱情况之间）而反向，但总ID转移始终在耗散尺度上导致正向能量级联，从而对湍流耗散做出积极贡献。 这支持了ID作为物理海洋学中的一种耗散机制的观点。 本研究提供了ID的一个基于物理的概述，并为理解导致湍流耗散的具体波波相互作用提供了见解。