GTP Seminar
Tuesday, 9 May 2006
2:30pm, FL2, Room 1001

Vortical and Wave Motion in Rotating
Stratified Turbulence

Michael Waite
NCAR
ASP/MMM


Abstract:
It can be useful to separate stably stratified flows into components with and without potential vorticity, corresponding to vortical motion and internal gravity waves, respectively.  These two types of motion have very different dynamics, and have motivated competing interpretations of the observed energy spectra in the atmosphere and ocean.  In this talk, we will present recent results concerning the dynamics and interactions of waves and vortices in the context of homogeneous rotating stratified turbulence with a linear wave--vortex decomposition.  We will begin with an examination of the statistical mechanical equilibrium of the truncated equations of motion -- a classical approach which provides new insight into the question of whether vortical energy cascades upscale in stratified turbulence (confirming that it does not).  We will then present numerical simulations of forced stratified turbulence with and without rotation.  We will show how the energy and transfer spectra and characteristic length scales vary with Froude and Rossby number; these quantities are very sensitive to the type of motion (vortical or wave or both) present.  In all cases it appears essential to resolve the vertical scale U/N, where U is the r.m.s. velocity and N is the Brunt-Väisälä frequency.  Possible implications for more realistic atmosphere and ocean models will also be discussed.