High trace‐velocity infrasound from pulsating auroras at Fairbanks, Alaska

Abstract

We report here on infrasound signals observed using the infrasound microphone array at Fairbanks, Alaska that are apparently associated with the presence of pulsating auroras near the zenith. We have investigated the frequency domain coherence between the luminous intensity of the pulsating auroras and the high trace‐velocity infrasound received at the earth's surface. Video data of the aurora display from an All‐Sky video camera on the night of December 5, 2003 was compared with the pressure waveform data from the eight‐microphone infrasonic array at Fairbanks. Enhanced coherence between the two signals was observed when a propagation delay time for the infrasound sample with respect to the video data sample was used. The frequency domain coherence was found to be high between the pulsating aurora intensity above the array and the high trace‐velocity infrasound signals at the surface in the pass band from 0.03 to 0.08 Hz. Ray‐tracing studies indicate that such high trace‐velocity infrasound signals originate from sources within 35 km of the zenith above the array for a source height of 110 km. The presence of pulsating aurora patches within this area during the time interval of received infrasound and the high coherence between the video and infrasound data lead us to believe that periodic heating of the atmosphere by pulsating aurora is the actual source of the observed high trace‐velocity infrasound.