The D Region Response to the August 2017 Total Solar Eclipse and Coincident Solar Flare

Abstract

During the solar eclipse of 21 August 2017, the University of Florida monitored very low frequency (3–30 kHz) radio activity at ten locations, enabling the remote sensing of the D region ionosphere (∼50‐ to 100‐km altitude). Two of the locations were far enough away (Antarctica) that no response to the eclipse was detected despite the fact that the eclipse significantly shadowed the transmitter. A particularly rare observation is presented: Three receivers were at locations where the Moon blocked at least some of the solar X‐ray flare that occurred near 1800 UT, providing high‐resolution observations of solar flare occultation by the Moon. The remainder of the sites registered meaningful responses to both the solar eclipse and the solar flare. Observations indicate that very low frequency signal propagation is affected once 30–55% obscuration is achieved anywhere along the propagation path. No long‐term or delayed effects, such as atmospheric gravity waves, were observed.

The Effect of the 21 August 2017 Total Solar Eclipse on the Phase of VLF/LF Signals

“…We found that for all three paths there was no noticeable influence on amplitude; however, the phase revealed a significant decrease during the eclipse. For the two signals transmitted from NPM and NML transmitters which both had frequencies close to 20 kHz the negative phase anomalies were −33° and −35°, correspondingly, which is in good agreement with the experimental results, obtained by Cohen et al () and Moore and Burch () for the American paths. Note that the anomalies lasted longer for the longer path.…”

“…No quantitative analysis of the ionospheric conditions during eclipse was made. Another work also presents the analysis of VLF signal during this eclipse (Moore & Burch, ). These authors observed both amplitude and phase perturbations on many middle length VLF paths from NLM transmitter.…”

Scattered Field Polarization for VLF Remote Sensing of Transient Events

“…When a sudden, localized disturbance occurs in the ionosphere between a VLF transmitter and receiver, the received signal is affected for a period of time, after which it recovers to (nearly) its original value. Such transients can be produced by a wide variety of events, including lightning (e.g., early/fast events, long recovery events, and lightning induced electron precipitation events), solar flares and eclipses [2], or even galactic γ-ray bursts.…”

Impact of Three Solar Eclipses of 2019–2020 on the D‐Region Ionosphere Observed From a Subtropical Low‐Latitude VLF Radio Station

“…(2012) used the solar obscuration profile along the propagation path to reproduce the observed VLF signal changes due to the total solar eclipse of 2009 and found the variation of the D‐region electron density during the eclipse period. Moore and Burch (2018) used a linear dependence of solar obscuration percentage for the VLF reflection height and slope of electron density parameter in the LWPC model to calculate the perturbed VLF amplitude during a solar eclipse. Besides the LWPC model, Inui and Hobara (2014), also used a 2D‐Finite Domain Time Difference (FDTD) method to simulate the VLF signal changes in Japan during the annular solar eclipse of 2012.…”