Thursday, 16 May 2002: 9:00 AM
A modeling investigation of near-cloud turbulence.
On 10 July 1997 a commercial passenger aircraft encountered severe turbulence near Dickinson, ND, en-route from Seattle to New York. The aircraft was negotiating a number of scattered thunderstorms, yet passed directly over a developing deep convective cloud. While passing over this cloud, the aircraft suffered accelerations of approximately two g's, in a period of about 10 seconds. Subsequently, twenty passengers and two flight attendants suffered minor injuries. This turbulence encounter motivates the current modeling study, which seeks to understand possible mechanisms causing the generation of turbulence in the clear-air directly adjacent to penetrating deep convection.
Two and three-dimensional cloud-resolving model calculations, with their configurations motivated by the turbulence encounter, will be presented. These calculations explicitly resolve both the convection and the turbulence-causing instabilities in the vicinity of the cloud. In particular, gravity waves are seen to break near the cloud top, causing vertical mixing and turbulence. In
addition to this gravity wave breakdown, smaller-scale Kelvin-Helmholtz-like waves form on the cloud interface. A discussion of these "near-cloud" turbulence-generating mechanisms will be presented with application to aviation