Long-Baseline VLF Observations of Solar Flares from Antarctica
Abstract
We present long-baseline Very Low Frequency (VLF) observations of solar flare-induced ionospheric disturbances obtained at the Bulgarian Polar Astronomical Observatory (St. Kliment Ohridski Base) on Livingston island, Antarctica. Using continuous VLF transmissions at 21.4 kHz (NPM, Hawaii) and 24.0 kHz (NAA, Maine), propagating over trans-hemispheric paths exceeding 11 000 km, we analyze observations of solar flares during the period 24 January-8 February 2025. After removing the strong diurnal signal via superposed epoch analysis, we analyse the flare-related perturbations in VLF amplitude and their correlation with GOES soft X-ray flux for 250 flares of C and M class. The long propagation paths provide enhanced sensitivity to flare-driven changes in D-region ionization. The observations reveal clear, frequency-dependent responses and measurable time delays between X-ray peaks and VLF extrema. These delays, including cases of near-zero or negative correlation lag for stronger events, are consistent with a possible role for flare spectral characteristics and D-region recombination processes, although alternative explanations related to waveguide propagation and signal-profile differences cannot presently be excluded. Our results demonstrate the scientific value of long-baseline Antarctic VLF observations for detecting and timing GOES-class flares, while also highlighting key limitations, such as background variability and path-dependent propagation effects, which must be quantified for reliable VLF-based flare monitoring.
Related
- Quasi-periodic pulsations in solar and stellar flares
- Type I Solar Radio Bursts Modulated by Solar Flares
- On the altitude profile of lower ionospheric D-region response time delay during solar flares
- Electron acceleration by turbulent reconnection in solar flares
- Electron Acceleration by Turbulent Reconnection in Solar Flares
BibTeX
@misc{kozarev2026longbaseline,
title = {{Long-Baseline VLF Observations of Solar Flares from Antarctica}},
author = {Kamen Kozarev and Peter Petkov and Ivaylo Nachev and Veselka Radeva and Momchil Dechev and Galin Borisov and Anton Atanasov},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2607.13913},
eprint = {2607.13913},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.13913},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Long-Baseline VLF Observations of Solar Flares from Antarctica
AU - Kamen Kozarev
AU - Peter Petkov
AU - Ivaylo Nachev
AU - Veselka Radeva
AU - Momchil Dechev
AU - Galin Borisov
AU - Anton Atanasov
PY - 2026
DA - 2026/10/07
PB - arXiv
DO - 10.48550/arxiv.2607.13913
UR - https://arxiv.org/abs/2607.13913
AB - We present long-baseline Very Low Frequency (VLF) observations of solar flare-induced ionospheric disturbances obtained at the Bulgarian Polar Astronomical Observatory (St. Kliment Ohridski Base) on Livingston island, Antarctica. Using continuous VLF transmissions at 21.4 kHz (NPM, Hawaii) and 24.0 kHz (NAA, Maine), propagating over trans-hemispheric paths exceeding 11 000 km, we analyze observations of solar flares during the period 24 January-8 February 2025. After removing the strong diurnal signal via superposed epoch analysis, we analyse the flare-related perturbations in VLF amplitude and their correlation with GOES soft X-ray flux for 250 flares of C and M class. The long propagation paths provide enhanced sensitivity to flare-driven changes in D-region ionization. The observations reveal clear, frequency-dependent responses and measurable time delays between X-ray peaks and VLF extrema. These delays, including cases of near-zero or negative correlation lag for stronger events, are consistent with a possible role for flare spectral characteristics and D-region recombination processes, although alternative explanations related to waveguide propagation and signal-profile differences cannot presently be excluded. Our results demonstrate the scientific value of long-baseline Antarctic VLF observations for detecting and timing GOES-class flares, while also highlighting key limitations, such as background variability and path-dependent propagation effects, which must be quantified for reliable VLF-based flare monitoring.
ER -