Pulsations in the Earth's Lower Ionosphere Synchronized with Solar Flare Emission

TL;DR

This study demonstrates that solar flare pulsations at X-ray and EUV energies cause synchronized, significant electron density variations in the Earth's lower ionosphere, revealing a closer coupling than previously understood.

Contribution

It provides the first evidence that the Earth's ionosphere responds to small-scale solar flare pulsations, showing a direct correlation between flare variability and ionospheric electron density changes.

Findings

Ionospheric D-region electron density varies by up to an order of magnitude during flare pulsations.

Ionosphere responds to solar flare pulsations with a timescale of approximately 20 minutes.

Earth's ionosphere is more sensitive to small-scale solar activity variations than previously believed.

Abstract

Solar flare emission at X-ray and extreme ultraviolet (EUV) energies can cause substantial enhancements in the electron density in the Earth's lower ionosphere. It is now become clear that flares exhibit quasi-periodic pulsations with timescales of minutes at X-ray energies, but to date, it has not been known if the ionosphere is sensitive to this variability. Here, using a combination of Very Low Frequency (24 kHz) measurement together with space-based X-ray and EUV observations, we report pulsations of the ionospheric D-region, which are synchronized with a set of pulsating flare loops. Modeling of the ionosphere show that the D-region electron density varies by up to an order of magnitude over the timescale of the pulsations ($\sim$20 mins). Our results reveal that the Earth's ionosphere is more sensitive to small-scale changes in solar soft X-ray flux than previously thought, and implies that planetary ionospheres are closely coupled to small-scale changes in solar/stellar activity.