Systematic Statistical Identification of Lower Region Acoustic Waves through VLF Remote Sensing

We present a method to automatically statistically characterize ionospheric acoustic wave (1-5 minute period) disturbances propagating through the lower region ionosphere (75- 85 km) by analyzing magnetic field recordings in the very-low- frequency (VLF) band. The ionosphere is an electrically charged layer at the top of the atmosphere (60-500 km) formed from solar radiation. The lowest region, known as the D-region (60- 90 km), is difficult to sense as it is above an elevation suitable for balloons yet below that of satellites. The ionosphere impacts global communications solutions due to its ability to transmit signals beyond line-of-sight to global distances. Acoustic waves are periodic moving oscillations that can disrupt conditions in the lower ionosphere. We describe a method to locate acoustic waves that relies on identifying outliers in the frequency spectrum of 30-minute periods of magnetic field data. These outliers may correlate to acoustic wave disturbances. Past studies of acoustic waves in the ionosphere have been anecdotal case studies. However, detailed information about their occurrences is needed to further reason about the causes of these disturbances, such as hurricanes, thunderstorms, space weather, and air turbulence over mountain ranges.