Phase Change Associated with Total Internal Reflection at a Strong Negative Gradient

Abstract

During an investigation of convergence-zone propagation in the Mediterranean, it was remarked that the explosion-pulse arrivals, which had suffered refraction at the extremely strong negative gradient near the surface, had been subjected to a drastic change of pulse shape. The first arrival that had suffered one deep refraction but no shallow refraction showed no evidence of change of pulse shape, except the normal broadening owing to absorption. The pulses were sampled and Fourier transforms were made, revealing that a phase-change independent of frequency of the order of π/2 had occurred in the case of arrivals with one shallow turning point, and one of the order of π for those with two shallow turning points. Theory predicts a phase change of π/2 on total internal reflection at an inhomogeneous layer and this could well be the cause of the effect observed; however, no evidence of phase change at the deep turning point has been found.