Monday, 10 February 2003: 9:15 AM
Aircraft Measurements of Turbulence: Length Scales, Spectra, Budgets, and the Prediction Problem
Four turbulence measurement campaigns were performed in the winter sub-tropical jet streams of south coastal Japan and Australia during 1998-2001 with the objective to capture the dynamics of severe refractive and clear air turbulence events. The aircraft used was the GROB 520T EGRETT, which is owned and operated by Airborne Research Australia a unit of Flinders University of South Australia. Severe turbulence events are very difficult to forecast and subsequently measure. They are of critical importance to many activities such as commercial air safety (NASA-FAA) and the evaluating High-Energy Laser (HEL) propagation disturbances. These aircraft measurements have shown that weak turbulence/severe turbulence events are associated with anisotropy/isotropy of the turbulent vertical velocity spectra/structure parameters. Strong turbulence events are associated with turbulent Froude number (from vertical heat flux equation) that approach unity with weaker turbulence with turbulent Froude numbers less than 1. The role that fluctuating velocity-pressure gradient correlations play in maintaining strong turbulence while critical is difficult to measure directly. There has been some success in using gradient Richardson number less than 1/4 derived from most recent radiosonde as a indicator of where (altitude) to measure for "strong turbulence". Some limitations of using diagnostic turbulence prediction schemes based on mesoscale model output will be considered as well as evolving measurement strategies to illuminate most important terms in a time dependent turbulence prediction model.