Areas of non-occurrence as well as areas of occurrence of high level clear air turbulence (CAT) over the South Pacific Region were determined during a selected five-day period in March, 1965. Latitude-longitude 'squares' of 2.5° were used to tabulate the flight data. Flights were divided into (1) flights at and below 30,000 feet and (2) flights above 30,000 feet. Frequency distributions and percentages of CAT occurrences were computed for geographical distributions, flight elevations and for various parameters mainly of a meteorological nature. In a general study covering all flight squares the most successful parameters were "average" vertical wind shear, vertical wind shear in the layer 10,000 feet below the maximum wind, presence of a jet stream, horizontal wind shear and Richardson's number, with maximum wind speed successful to a lesser extent, mainly in the lower layer. Most parameters were more successful in the lower layer where turbulence was more frequently encountered, an exception being horizontal wind shear which gave the best results in the higher layer. There was a high incidence of CAT. 52 percent of flights encountered CAT and 22 percent encountered moderate or severe CAT. Five parameters - Endlich's turbulence index, "average" vertical wind shear, Richardson's number, vorticity and vorticity advection - were included in a restricted study covering flight squares in the area bounded by latitudes 22½°s and 40°S and longitudes 112½°E and 160°E. "Average" vertical wind shear gave the best results.
Colquhoun et al. (Thu,) studied this question.