Very low frequency subionospheric remote sensing of thunderstorm‐driven acoustic waves in the lower ionosphere

Abstract

We present observations of narrowband subionospheric VLF transmitter signals on 20 March 2001, exhibiting coherent fluctuations of over 1 dB peak to peak. Spectral analysis shows that the fluctuations have periods of 1–4min and are largely coherent. The subionospheric propagation path of the signal from Puerto Rico to Colorado passes over two regions of convective and lightning activity, as observed by GOES satellite imagery and National Lightning Detection Network lightning data. We suggest that these fluctuations are evidence of acoustic waves launched by the convective activity below, observed in the 80–90 km altitude range to which nighttime VLF subionospheric remote sensing is sensitive. These observations show that VLF subionospheric remote sensing may provide a unique, 24h remote sensing technique for acoustic and gravity wave activity. We reproduce this event in simulations using a fluid model of gravity and acoustic wave propagation to calculate the ionospheric disturbance, followed by an electromagnetic propagation model to calculate the perturbation amplitude at the location of the VLF receiver. Simulation results show that a very large and coherent convective source is required to produce these amplitude perturbations.

Ionospheric response to infrasonic‐acoustic waves generated by natural hazard events

“…Waves above the Brunt-Väisälä frequency (>3.3 mHz, periods <5 min) have also been detected in mesospheric airglow spectral data [Pilger et al, 2013a[Pilger et al, , 2013b, consistent with acoustic or evanescent waves near the acoustic cutoff frequency; remote sensing of the D region likewise reveals short acoustic and gravity wave periods [Lay and Shao, 2011;Marshall and Snively, 2014]. Recent GPS observations of ionospheric TEC following the Moore, Oklahoma EF5 tornado-producing storm revealed ∼4 min periodicities southward of the storm center [Nishioka et al, 2013], illustrating clearly the direct spatial and temporal connections between tropospheric weather and localized periodic disturbances of the F region ionosphere.…”

“…Simulations directed toward investigating the observable signatures of acoustic waves have also been reported, for the hydroxyl airglow response [Snively, 2013], the effects on subionospheric very low frequency electromagnetic propagation [Marshall and Snively, 2014], and the coupled F region ionospheric response [Zettergren and Snively, 2013]. Results suggest that waves with compressional velocities ∼10s-100s m/s can detectably perturb each system.…”

Semi-annual oscillation (SAO) of the nighttime ionospheric D region as detected through ground-based VLF receivers

“…Because the D region's formation and chemistry are tightly bound to the neutral MLT (Brasseur and Solomon, 2005), it is believed that the D region is affected by the same forcings, experiencing similar oscillations (e.g., Schmitter, 2011;Silber et al, 2013;Marshall and Snively, 2014). As far as the current authors know, there are no previous works showing the SAO dominating the natural long-term oscillations in the nighttime D region apart from the work of Toledo-Redondo et al (2012), who presented a SAO indication within the equatorial latitudes by using space-based ELF-VLF data from the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) micro-satellite.…”

A Study on the VLF/LF Long Term Amplitude Oscillations Associated with Frequencies 37.5 kHz and 45.9 kHz Received at Keil Longwave Monitor, Keil, Germany

“…The chemistry and formation of D-layer infer to be neutral environment and therefore, experience oscillations [12] [13]. To study this region was a tedious and difficult job till the discovery of remote sensing.…”