Effect of Atmospheric Variability and Aircraft Flight Parameters on the Refraction of Sonic Booms

Abstract

This study deals with the potential audibility of sonic booms from supersonic aircraft at the ground as a consequence of the aircraft flight parameters and the atmospheric variability. A ray tracing model is used to decide whether a sonic boom emitted downwards by a high flying supersonic aircraft hits the ground or is refracted upwards before it reaches the ground. Aircraft altitude, speed, and flight direction are systematically changed within realistic ranges. The meteorological data rely on a homogeneous reanalysis dataset for eleven years over the domain of Europe with a very high vertical resolution. The cases of sonic booms hitting or not hitting the ground are identified for various situations and respective frequency distributions are derived. In addition, the angle of incidence of rays arriving at the ground and the turning-level height of rays not reaching the ground are studied as the intensity of sonic booms also depends on these parameters. It turned out that sonic-boom rays are refracted such that they do not reach the ground if the flight altitude is rather high (long propagation path) and the aircraft speed remains between Mach numbers of 1.05 and 1.25. Sonic-boom rays not reaching the ground are furthermore possible if the aircraft heading is mainly upwind, the temperature mostly increases along the propagation direction of the ray, and a wind speed maximum exists below flight level. The probability of sonic-boom rays not reaching the ground generally increases from north to south, but also depends on the season.