Internal gravity waves play a primary role in geophysical fluids: They contribute significantly to mixing in the ocean, and they redistribute energy and momentum in the middle atmosphere. Until recently, most studies were focused on plane wave solutions. However, these solutions are not a satisfactory description of most geophysical manifestations of internal gravity waves, and it is now recognized that internal wave beams with a confined profile are ubiquitous in the geophysical context. We discuss the reason for the ubiquity of wave beams in stratified fluids, which is related to the fact that they are solutions of the nonlinear governing equations. We focus more specifically on situations with a constant buoyancy frequency. Moreover, in light of recent experimental and analytical studies of internal gravity beams, it is timely to discuss the two main mechanisms of instability for those beams: (a) the triadic resonant instability generating two secondary wave beams and (b) the streaming instability corr...

中文翻译：

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内重力波束的不稳定性

内部重力波在地球物理流体中起着主要作用：它们对海洋中的混合有很大贡献，并且它们在中层大气中重新分配能量和动量。直到最近，大多数研究都集中在平面波解决方案上。然而，这些解决方案并不能令人满意地描述内部重力波的大多数地球物理表现，现在人们认识到具有受限剖面的内部波束在地球物理环境中无处不在。我们讨论了波束在分层流体中普遍存在的原因，这与它们是非线性控制方程的解有关。我们更专注于具有恒定浮力频率的情况。此外，根据最近对内部重力梁的实验和分析研究，