A Preliminary Study of Atmospheric Effects on the Sonic Boom

Abstract

Atmospheric effects on sonic booms generated by bomber and fighter aircraft are investigated through analysis of more than 4000 sonic-boom pressure traces obtained from a 40-microphone grid at Edwards Air Force Base, Calif., during the fall and winter of 1966–67. A computer program, which generates maximum overpressure values for a horizontally stratified real atmosphere, is tested against the mean observed overpressure on the grid and is shown to be in error by an average of 10% when the maximum observed overpressure is derived from the positive impulse area. The pressure traces are grouped into three categories, so that “spiked” signatures, which constitute the largest deviation from the mean, may be studied as a function of local weather conditions. This study shows a good correlation between depth of the surface mixed layer and the percentage of spiked signatures. The variability of the maximum overpressure also increases with increase in low-level wind speed. Both these results suggest that turbulence in the planetary boundary layer is the main cause of spiked signatures and the associated large variation in maximum overpressure. There is some evidence that waves within an inversion contribute to overpressure variability on a larger scale.