The Earth’s magnetosphere is the outermost layer of the geospace system deflecting energetic charged particles from the Sun and solar wind. The solar wind has major impacts on the Earth’s magnetosphere, but it is unclear whether the same holds for solar flares—a sudden eruption of electromagnetic radiation on the Sun. Here we use a recently developed whole geospace model combined with observational data from the 6 September 2017 X9.3 solar flare event to reveal solar flare effects on magnetospheric dynamics and on the electrodynamic coupling between the magnetosphere and its adjacent ionosphere, the ionized part of Earth’s upper atmosphere. We observe a rapid and large increase in flare-induced photoionization of the polar ionospheric E-region at altitudes between 90 km and 150 km. This reduces the efficiency of mechanical energy conversion in the dayside solar wind–magnetosphere interaction, resulting in less Joule heating of the Earth’s upper atmosphere, a reconfiguration of magnetosphere convection, as well as changes in dayside and nightside auroral precipitation. This work thus demonstrates that solar flare effects extend throughout the geospace via electrodynamic coupling, and are not limited—as previously believed—to the atmospheric region where radiation energy is absorbed1.
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Source data are provided with this paper. All other used data are available from the corresponding author upon reasonable request. The GNSS TEC and AMPERE FACs datasets are available from http://millstonehill.haystack.mit.edu/ and http://ampere.jhuapl.edu/. EISCAT radar and Inuvik high-frequency radar data are available from https://portal.eiscat.se/madrigal/ and http://vt.superdarn.org/tiki-index.php?page=DaViT+RTP, respectively. THEMIS data are available from http://themis.ssl.berkeley.edu. OMNI solar wind data are available from the CDAWeb website (https://cdaweb.gsfc.nasa.gov/index.html/). Solar irradiance data are provided by the NOAA National Geophysical Data Center (NGDC) GOES website (https://www.ngdc.noaa.gov/stp/satellite/goes/index.html).
The computer code (LTR) to simulate the geospace response to solar flares is available from the corresponding author upon request.
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This work is supported by the Strategic Priority Research Program of Chinese Academy of Sciences grant no. XDB 41000000, NSF of China 42074188 and 42030202, and US NSF Awards 1739188, 1522133 and AGS1452309. We acknowledge the use of data from the Chinese Meridian Project. We thank Q. Shi and W. Shang for helpful discussions.
The authors declare no competing interests.
Peer review information Nature Physics thanks Matthias Förster and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended Data Fig. 1 Interplanetary solar wind parameters and x-ray intensity.
a, Interplanetary magnetic field components, Bx, By, and Bz in nT; b, solar wind number density in cm−3; c, solar wind velocity components, Vx, Vy, and Vz in km/s; and (d) X-ray intensity on September 6, 2017 integrated over wavelengths from 0.1 to 0.8 nm observed by the GOES satellite (red line), calculated from FISM (blue line), and without solar flare effects (black line). Horizontal dotted lines represent zero Y-axis reference lines in panels a and c.
Extended Data Fig. 2 Solar flare effects on the polar ionosphere.
Universal time and altitude variations of electron density (Ne), electron temperature (Te), and ion temperature (Ti) from LTR flare simulations (left panels) and EISCAT Tromsø VHF radar (right panels) on 6 September 2017. Since the VHF radar was pointing at geographic north with 30° elevation angle, the latitudinal coverage is about 69°–72° for 80–400 km altitude.
Extended Data Fig. 3 LTR-simulated Hall conductance ∑H for pre-flare and flare-peak intervals.
Comparison of 10-minute average LTR simulated Hall ∑H conductance for pre-flare (11:44–11:53 UT, a, flare-peak (12:10–12:19 UT, b, intervals on September 6, 2017. Polar plots are in magnetic latitude-local time (MLT) coordinates as in panel a.
Extended Data Fig. 4 Spacecraft measurements from THEMIS TH-A and TH-E.
From top to bottom are magnitude of magnetic field a, e, ion density b, f, bulk flow c, g, and ion spectra d, h. The four horizontal axes in the bottom panels stand for X (Xgsm), Y (Ygsm), and Z (Zgsm) components in the Geocentric Solar Magnetospheric System coordinate, and universal time (UT).
Source Data Fig. 1
Numerical simulated TEC used to generate Fig. 1.
Source Data Fig. 2
Numerical simulated FACs used to generate Fig. 2.
Source Data Fig. 3
Numerical simulated velocity used to generate Fig. 3.
Source Data Fig. 4
Numerical simulated CPCP and Joule heating rate used to generate Fig. 4.
Source Data Extended Data Fig. 2
Numerical simulated Ne, Te and Ti used to generate Extended Data Fig. 2.
Source Data Extended Data Fig. 3
Numerical simulated Hall conductance used to generate Extended Data Fig. 3.
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Liu, J., Wang, W., Qian, L. et al. Solar flare effects in the Earth’s magnetosphere. Nat. Phys. 17, 807–812 (2021). https://doi.org/10.1038/s41567-021-01203-5