A case study of convectively-induced clear air turbulence

On 5 August 2005, two commercial 757 airliners encountered severe turbulence over Northwest Indiana, at cruising altitude in the ostensibly clear air after having flown over or around a large convective storm. According to contemporaneous satellite imagery, the planes were roughly 20 km away from any cloud having appreciable optical depth. Turbulence episodes like these are of interest to the aviation community because they occur without warning and cannot be detected by instruments presently on board aircraft.

WRF model simulations in real-data and idealized modes have been used to eludicate the forcing mechanisms of this convectively-induced clear air turbulence event. The real-data simulations successfully capture the rapid growth of the strong convection that occurred along a synoptic- scale cold front. Comparisons of real-data runs in which latent heating is permitted or not allowed show that this convection served to modify its surrounding environment in a zone stretching some distance beyond the anvil and in a manner that lowered the Richardson number in that zone to the critical value for turbluence generation. Other case studies will be examined in this effort to understand the general nature and causes of convectively-induced turbulence.