Linking Solar Flare Observations to a Series of Impulsive Solar Energetic Particle Events Measured with Solar Orbiter at 0.5 AU

Impulsive solar energetic particle (SEP) events are typically associated with solar flares but the related particle injection and acceleration processes are still not well understood. We use in-situ and remote-sensing data from Solar Orbiter to establish a plausible link between a series of eruptions in a flaring region and a sequence of four SEP events measured at 0.5 AU between 5 and 6 March 2022. The direct comparison between these four events from the same source region allows to study the variability of the injected SEPs during an extended period of magnetic connectivity between Solar Orbiter and the flaring active region. In this study we analyze energetic electron, proton, and heavy ion data provided by the Energetic Particle Detector (EPD) suite onboard Solar Orbiter. Via a velocity dispersion analysis (VDA) of all measured particle species we estimate the solar event onset times which coincide with a series of solar eruptions that is observed by the Extreme Ultraviolet Imager (EUI) and the Spectrometer Telescope for Imaging X-rays (STIX) onboard Solar Orbiter. Further high-time-resolution EUV images and photospheric magnetic field information of the related active region is given by the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory. Solar Orbiter and Earth were nearly perfectly radially aligned at this time which enabled this additional remote sensing by SDO. We find that the energy spectra of the heavy ion in-situ measurements show significant differences between the four investigated SEP events in terms of overall particle intensity, spectral slope, and ³He / ⁴He abundances. By comparison with the remote-sensing observations we find that the two stronger SEP events (with higher ³He / ⁴He ratios) are related to solar eruptions with a more complex eruption pattern leading to extended brightening and restructuring of coronal loop structures. These new detailed observations can be used as starting point for quantitative modelling of flare-associated energetic particle acceleration and release in active regions.

This work has been funded by the Spanish Ministerio de Ciencia, Innovación y Universidades project PID2019-104863RBI00/AEI/10.13039/501100011033.