The Effect of Atmospheric Variability on Infrasound Propagation

Natural changes in the background atmospheric state variables greatly influence infrasonic signal propagation characteristics on time scales from hours to months and over horizontal spatial scales greater than about 750 km. Complexity arises from inherent atmospheric variability across all levels. Using state-of-the-art acoustic propagation codes and measured atmospheric profiles, the influence of atmospheric variability on infrasound signals is modeled and discussed. Several illustrative examples are presented. Calculations of the temporal evolution of the propagation characteristics for representative locations and time intervals are shown. In addition, instantaneous global maps of the percentage of signals ducted in the troposphere, stratosphere, and lower thermosphere, as well as escaping to ionospheric levels, are presented. The prospects for using observed infrasonic signals to infer the state of the atmosphere is also discussed.