Speaker
Description
The fleet of spacecraft distributed in the inner heliosphere during May-June 2024 offered us the unique opportunity to analyze, over a wide range of heliolongitudes, the effects produced by the complex sunspot group formed by the NOAA active region (AR) 13664 (later numbered AR 13697).
The intense level of solar activity recorded from 2024 May 8 to 2024 June 21 led to unusually elevated energetic particle intensities observed by a number spacecraft at heliocentric distances $<$1 au including Solar Orbiter, Parker Solar Probe, STEREO-A, and near-Earth spacecraft.
The result was a long-time interval ($>$40 days) with elevated ($>$10 MeV) proton intensities observed over at least a heliolongitude span of $\sim$170$^{\circ}$.
Among this intense period of activity, a major solar energetic particle (SEP) stood out because of its large intensity, its association with both a fast ($\sim$1500 km s$^{-1}$) halo coronal mass ejection (CME) and an intense X-ray flare (with an estimated class X16.5) occurring at a longitude $\sim$170$^{\circ}$ with respect to Earth
The peculiar proton energy spectra measured near Earth (flattening over the energy range 30-80 MeV), the formation of an heliospheric energetic particle reservoir displaying similar particle intensities that extended over a longitude span of $\sim$170$^{\circ}$ and for a period of $\sim$2 weeks makes this event exceptional.
We propose several mechanisms to explain the spread of SEPs during this intense event and the formation of this energetic particle reservoir, including particle acceleration over a broad CME-driven shock, efficient particle transport across the interplanetary magnetic field, and particle reflection and redistribution from some distance beyond 1~au where prior CMEs merged.
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