PSP/IS⊙IS observations of the 29 November 2020 solar energetic particle event

Year: 2021

DOI: 10.1051/0004-6361/202140967

Aims. On 29 November 2020, at 12:34 UT, active region 12790 erupted with an M4.4 class flare and a 1700 km s⁻¹ coronal mass ejection. Parker Solar Probe (PSP) was completing its seventh orbit around the Sun and was located at 0.8 au when the Integrated Science Investigation of the Sun (IS⊙IS) measured the ensuing mid-sized solar energetic particle (SEP) event. Not only was this the first SEP event with heavy ions above 10 MeV nuc⁻¹ to be measured by IS⊙IS, it was also measured by several spacecraft positioned around the Sun, making it the first circumsolar event of solar cycle 25. Here we describe an overview of the SEP event characteristics at PSP.

Methods. Fluence spectra for electrons, H, He, O, and Fe were calculated for the decay portion of the event. For the entire time period of the event, it was possible to calculate fluence spectra for electrons, O, and Fe only due to instrumental mode changes in one of the IS⊙IS telescopes, affecting H and He during the period of peak intensities. Using higher time resolution data, we also studied the onset of the event and temporal variations in the particle intensities at the shock and during the magnetic cloud passage.

Results. During the decay, the ion spectra are consistent with power laws at low energies with an exponential rollover at a few MeV nuc⁻¹, while the electron spectrum is consistent with a power law of index −5.3. Based on fits to the spectra, Fe/O and He/H abundance ratios as a function of energy are calculated and found to be nominal for large SEP events at hundreds of keV/nuc, but decrease strongly with increasing energy. The full-event spectra for O and Fe have similar shapes to those of the decay, but with higher roll-over energies. The electron spectrum for the full event is harder with an index of −3.4 and there is some evidence of higher energy components near ∼2 MeV and above ∼4 MeV. Despite the spacecraft being tilted 45° with respect to the nominal orientation of the spacecraft's long axis pointed towards the Sun, there is some anisotropy apparent in MeV protons during the onset of the event. Velocity dispersion is also evident, consistent with a solar release time of 13:15 UT and pathlength of 1.3 au. The arrival of the related magnetic cloud resulted in the suppression of SEP intensities, although a brief increase in particle intensities suggests PSP moved out of the cloud for ∼30 min. This appears to be the first medium-sized event in the rise of cycle 25 activity, with additional large events likely to occur. Additional details of the event beyond this overview can be found in several related papers.