A review on the spontaneous generation of gravity waves

Abstract This review provides a comprehensive examination of the spontaneous generation of inertia–gravity waves (IGWs) in atmosphere, integrating theoretical, observational, numerical, and laboratory perspectives. Beginning with the fundamentals of balanced motion—geostrophic and hydrostatic equilibria—it explores the Rossby-number–governed separation of slow, large-scale flows from fast IGW modes. Theoretical analyses based on the primitive equations and slow-manifold expansions reveal that even infinitesimal imbalances inexorably excite exponentially small IGW amplitudes via a Stokes-phenomenon mechanism. Observational studies—from radiosonde networks and clear-air radars to satellite limb sounders and aircraft measurements—delineate the energy and spatial distribution of waves originating from orography, convection, jets, and fronts, while also highlighting instrumental and interpretive limitations. Idealized numerical simulations of frontogenesis and baroclinic life cycles confirm key emission pathways and underscore sensitivity to grid resolution and dissipation. Complementary rotating-tank experiments replicate baroclinic instabilities and support the inevitability of wave emission across parameter regimes. The review further discusses the pivotal role of IGWs in atmospheric momentum and energy transport—shaping stratospheric circulation, oscillations, and turbulence—and identifies persistent challenges in parameterizing gravity-wave effects in large-scale models. By synthesizing multi-scale evidence, this work summarizes current understanding and outlines pathways for future research, including enhanced observational coverage, high-resolution modeling, and improved representation of nonorographic wave sources.