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. The time and location of 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 evaluating refractive turbulence effects on High-Energy Laser (HEL) propagation. These aircraft measurements have shown that weak turbulence/severe turbulence events are associated with anisotropy/isotropy of the velocity spectra or structure parameters. Strong turbulence events are associated with flux Richardson numbers that are ≤ 0.4 while weaker turbulence has flux Richardson numbers ≥ 1. Fluctuating velocity-pressure gradient correlations play a critical in maintaining strong turbulence. Some success can be expected in using bulk gradient Richardson number ≤ 1/4 as a correlator of moderate to strong turbulence.