Abstract

Co-author: Brad Marston (Brown University)

We present Direct Statistical Simulation (DSS) of jet formation. We consider the simplest barotropic model both on a spherical surface and a local beta-plane. DSS involves the direct solution of the low-order statistics via an expansion in cumulants. In both cases we compare the results of our DSS with statistics obtained from long DNS simulations. We discuss in what circumstances truncating the cumulant expansion at second order (thereby including eddy mean-flow interaction but neglecting eddy-eddy interactions for the fluctuating fields) gives a good description of the dynamics of the flow. We demonstrate that this depends on the degree of lack of statistical equilibrium in the flow (as measured by the Zonostrophy parameter). We discuss briefly how to proceed to higher order to include eddy-eddy interactions and the possibility of forward and inverse cascades.