Wave‐Enhanced Tracer Dispersion

Abstract

AbstractRecent oceanic datasets indicate high gravity wave‐to‐balance energy ratio at submesoscales. Idealized investigations exploring such wave‐dominated regimes have found that waves can break up coherent vortices and generate energetic small scale flow structures, indicating that the turbulence phenomenology is very different in wave‐dominated regimes when compared to the quasi‐geostrophic regime. Motivated by these recent investigations revealing significant differences in the flow dynamics in quasi‐geostrophic and wave‐dominated regimes and multiple oceanic observations pointing out enhanced tracer stirring at submesoscales, in this paper we compare and contrast passive tracer dispersion by barotropic flows in quasi‐geostrophic and wave‐dominated turbulent regimes using the reduced model explored by Thomas and Yamada (2019), https://doi.org/10.1017/jfm.2019.465. On comparing passive tracer dispersion by barotropic flows in the two different regimes, we find that wave‐dominated turbulent flows stir and mix tracer fields much more rapidly than quasi‐geostrophic turbulent flows that consist of well‐defined coherent vortices. The presence of energetic small‐scale features in wave‐dominated flows increases small‐scale turbulent diffusivity and results in steeper tracer variance spectrum in wave‐dominated flows compared to the quasi‐geostrophic flows. Our findings point out that gravity waves can play an indirect role in enhancing tracer dispersion: waves modify the flow, generating energetic small‐scale structures, that makes stirring of tracers more efficient. Despite our study being idealized, we speculate the qualitative phenomenology of waves indirectly enhancing tracer dispersion to be of significance at submesoscales in the world's oceans.