Comparison of Thorpe and Ozmidov Length Scales from Direct Numerical Simulations

Abstract:

The Thorpe scale, a measure of the length scale of turbulent overturning events, is compared to the Ozmidov scale in direct numerical simulations (DNS) of gravity wave and fine structure interactions in this study. Such a comparison has significant and practical implications for deriving global climatology of important atmospheric turbulence parameters such as energy dissipation rates from routine high vertical resolution radiosonde data as suggested by Clayson and Kantha (2008). The DNS results can determine exactly all the turbulence quantities needed to evaluate Thorpe scale and Ozmidov scale in the simulation results thus can be employed to assess the accuracy and universality of expressions relating the two length scales identified in previous field measurements and other simulation results. We evaluate the ratio of the two length scales for an entire computational domain containing multiple turbulence events or for individual events in a subset of the full domain. This allows an evaluation of the possible dependence of the ratio on instability character, Re and other flow parameters.