Velocity Dispersion of Solar Energetic Particles in the Turbulent Heliosphere
- 1University of Lancashire
Abstract
Solar energetic particles (SEPs) are a signature of solar eruptions, and to link them to acceleration mechanisms many studies investigate their injection time at the Sun, t Sun . We assess velocity dispersion analysis (VDA), an often-used method to derive t Sun . We use full-orbit simulations of 1–100 MeV SEP protons in our recent new model of the interplanetary magnetic turbulence superposed on a Parker spiral magnetic field. The turbulence is described analytically as dominant transverse fluctuations that are 2D with respect to the mean field, supplemented with a minor contribution of asymptotically slab turbulence modes. We determine simulated SEP intensities for four turbulence strengths and use VDA to obtain t Sun and the apparent path length s of the SEPs, employing an SEP onset threshold to mimic a realistic energetic proton background before the SEP event. We find that turbulence strongly affects t Sun and s . For weak to strong turbulence, VDA estimates of t Sun are 2–30 minutes after the actual solar injection time, and the path lengths are 0.2–5 au longer than the Parker spiral. For very strong turbulence, the path lengths are > 5 au, considerably longer than those typically obtained from SEP observations. We also investigate the effect of energy dependence of the pre-event proton background, and find that different background spectra result in 5–20 minutes difference in VDA injection times, depending on the heliolongitude. We conclude that in many cases VDA-derived injection times include a significant contribution from turbulence and/or the pre-event background and are not an accurate estimate of the acceleration time.
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BibTeX
@article{laitinen2026velocity,
title = {{Velocity Dispersion of Solar Energetic Particles in the Turbulent Heliosphere}},
author = {T. Laitinen and S. Dalla},
journal = {The Astrophysical Journal Letters},
year = {2026},
month = oct,
doi = {10.3847/2041-8213/aeae2a},
url = {https://iopscience.iop.org/article/10.3847/2041-8213/aeae2a},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Velocity Dispersion of Solar Energetic Particles in the Turbulent Heliosphere
AU - T. Laitinen
AU - S. Dalla
PY - 2026
DA - 2026/10/16
JO - The Astrophysical Journal Letters
DO - 10.3847/2041-8213/aeae2a
UR - https://iopscience.iop.org/article/10.3847/2041-8213/aeae2a
AB - Solar energetic particles (SEPs) are a signature of solar eruptions, and to link them to acceleration mechanisms many studies investigate their injection time at the Sun, t Sun . We assess velocity dispersion analysis (VDA), an often-used method to derive t Sun . We use full-orbit simulations of 1–100 MeV SEP protons in our recent new model of the interplanetary magnetic turbulence superposed on a Parker spiral magnetic field. The turbulence is described analytically as dominant transverse fluctuations that are 2D with respect to the mean field, supplemented with a minor contribution of asymptotically slab turbulence modes. We determine simulated SEP intensities for four turbulence strengths and use VDA to obtain t Sun and the apparent path length s of the SEPs, employing an SEP onset threshold to mimic a realistic energetic proton background before the SEP event. We find that turbulence strongly affects t Sun and s . For weak to strong turbulence, VDA estimates of t Sun are 2–30 minutes after the actual solar injection time, and the path lengths are 0.2–5 au longer than the Parker spiral. For very strong turbulence, the path lengths are > 5 au, considerably longer than those typically obtained from SEP observations. We also investigate the effect of energy dependence of the pre-event proton background, and find that different background spectra result in 5–20 minutes difference in VDA injection times, depending on the heliolongitude. We conclude that in many cases VDA-derived injection times include a significant contribution from turbulence and/or the pre-event background and are not an accurate estimate of the acceleration time.
SN - 2041-8205
SN - 2041-8213
ER -