Sack Lunch Seminar (SLS)

How energy moves around between different spatial scales and classes of flow is an important but still poorly understood question aspect of ocean circulation. Here we consider energy fluxes in two different dynamical models. The first revisits the classic quasigeostrophic double gyre problem. We find substantial differences from the phenomenology of geostrophic turbulence, which has mostly been worked out assuming periodic or unbounded domains. In particular, the nonlinear inverse energy cascade familiar from studies of 2-dimensional and geostrophic turbulence does not extend between energy source and sink scales, as is commonly supposed. Rather, it is part of a "double cascade" in which the linear beta term allows for a forward cascade of energy. This forward beta cascade is essentially equal and opposite to the nonlinear cascade. In a separate study, we also consider interactions between slow (geostrophic) and fast (near-inertial) modes in a primitive equation channel. Forcing includes steady and high frequency components and we find that near-inertial oscillations excited by the high frequency forcing can have a significant impact on the low frequency part of the solution. Typically, the near-inertial modes act to drain energy from the geostrophic flow.