Solar proton events (SPE) and the frequency decrease
Solar proton events (SPE) are outbursts of energetic protons from the Sun, which — unlike X-ray radiation — penetrate into the lower part of the D-region (approximately 50-60 km) and ionize it primarily in the polar regions, where the magnetic field cannot deflect them.
Solar proton events (SPE) are outbursts of energetic protons from the Sun, which — unlike X-ray radiation — penetrate into the lower part of the D-region (approximately 50-60 km) and ionize it primarily in the polar regions, where the magnetic field cannot deflect them.
This additional ionization in the lower layer of the cavity acts on the SR in the opposite way to X-ray flares: the SR frequency decreases, on the order of ~3-4 % Singh 2014Satori 2016. The decrease reflects a change in the conductivity profile of the cavity at its lower edge and the lossy characteristics of the polar ionosphere during the event.
The opposite sign of the response (X-ray → increase, protons → decrease) is diagnostically valuable: it makes it possible to infer from the behavior of the SR frequency which type of solar disturbance is currently underway. The simultaneous occurrence of both phenomena during large flares may partially compensate their contributions.
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Sources
- Satori2016Sátori, G., et al. (2016). Effects of Energetic Solar Emissions on the Earth–Ionosphere Cavity of Schumann Resonances. Surveys in Geophysics, 37, 757–789.Open source
- Singh2014Singh, B., et al. (2014). X-rays and solar proton event induced changes in the first mode Schumann resonance frequency observed at a low latitude station Agra, India. J. Atmos. Sol.-Terr. Phys.Open source