An Investigation of Turbulent Processes in the Lower Stratosphere

The equations that govern turbulent motion have not been widely applied to above the planetary boundary layer mainly because of spatial and temporal restrictions to available data. Numerical model simulations can be configured for spatial and temporal resolutions necessary to evaluate the turbulent kinetic energy (TKE) and eddy dissipation rate (EDR) tendency equations. Since there is no prescribed limitation as to where the tendency equations can be applied, one may investigate contributions to turbulent processes at any level in the atmosphere.

The full TKE and EDR tendency equations are computed explicitly at vertical levels between 9 and 22 kilometers for several different case studies. The horizontal spatial scales of the TKE and EDR budgets range between 71 and 222 meters, and incorporate averages and perturbations over a 13 to 36 minute time period. A finite difference scheme is applied to all vertical derivatives within the tendency equations at a resolution of 250 m, closely matching the respective horizontal length scales.

The budget calculations indicate that processes such as meridional and zonal advection, commonly ignored in boundary layer processes, can provide a non-negligible contribution to turbulence creation and destruction in the lower stratosphere. For a large- amplitude surface gravity wave case, the budgets reveal turbulence creation and destruction from a convectively-generated vertically propagating gravity wave well into the stratosphere, several kilometers above the maximum vertical velocity. The results suggest that turbulence creation and destruction exist at levels far above the source, and can pose a threat to aircraft that fly at these altitudes.