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

Abstract

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.

Direct First Parker Solar Probe Observation of the Interaction of Two Successive Interplanetary Coronal Mass Ejections in 2020 November

“…CME2 gave rise to an unusual spread of energetic particles that are considered to be the first widespread solar energetic particle (SEP) event of solar cycle 25 (Cohen et al 2021;Kollhoff et al 2021;Lario et al 2021;Mitchell et al 2021;Kouloumvakos et al 2022). Two out of the four CMEs observed by solar and heliospheric telescopes, namely CME1 and CME2, impacted PSP and left clear flux rope imprints detected by the magnetometer (FIELDS; Bale et al 2016) on board.…”

Comparative Analysis of the 2020 November 29 Solar Energetic Particle Event Observed by Parker Solar Probe

“…During the SEP event on 2020 November 29, intensities were high enough to trigger the pre-established intensity thresholds at different energies. The EPI-Hi particle intensities displayed in this paper have been corrected for changes in the geometric factors that resulted from the varying energy thresholds of the instrument during this period (see details in Cohen et al 2021).…”

“…The exit of PSP from ICME-1 was marked by an increase in 8 MeV proton intensities in such a way that intensities at different energies were similar, leading to a relatively flat spectrum (γ ∼ 0). Unfortunately, changes in the energy threshold mode used by EPI-Hi occurring close to shock passage (Cohen et al 2021) resulted in data gaps that do not allow us to see the complete evolution of the high-energy proton intensities before the arrival of S2 (see Figure 1(a)). The low-energy (8 MeV) proton intensities peaked with the arrival of the shock S2, which was followed by a period of elevated intensities throughout the sheath region of ICME-2.…”

“…As expected, the IP counterpart of this CME (henceforth ICME-2) arrived at PSP on 2020 December 1 (day of year 336), preceded by the passage of an IP shock at 18:35 UT on 2020 November 30 (henceforth S2). An overview of the energetic particle observations by the Integrated Science Investigation of the Sun (ISeIS; McComas et al 2016) on board PSP has been presented by Cohen et al (2021), whereas detailed observations of the SEP event by the multiple spacecraft distributed at heliocentric distances 1 au have been described by Kollhoff et al (2021).…”

CMEs and SEPs During November-December 2020: A Challenge for Real-Time Space Weather Forecasting

“…Both commenced from the same source region, AR 12790, which was still behind the Earth-facing eastern limb at the time of Flare1, indicating that its "true" X-ray class might have been even higher than observed. The first of these eruptions has already gained significant attention, since it was associated with the first widespread SEP event of Solar Cycle 25 and with a CME detected in situ by the Parker Solar Probe and STEREO-A spacecraft (e.g., Cohen et al, 2021;Giacalone et al, 2021;Kollhoff et al, 2021;Kouloumvakos et al, 2022;Lario et al, 2021;Mason et al, 2021;Mitchell et al, 2021;Möstl et al, 2022;Nieves-Chinchilla et al, 2022). The configurations of planets and spacecraft within the orbit of Mars on the days of the two flares are shown in Figure 1.…”