Analyses of ∼0.05–2 MeV Ions Associated with the 2022 February 16 Energetic Storm Particle Event Observed by Parker Solar Probe

Abstract

We present analyses of 0.05–2 MeV ions from the 2022 February 16 energetic storm particle event observed by Parker Solar Probe's (PSP) IS⊙IS/EPI-Lo instrument at 0.35 au from the Sun. This event was characterized by an enhancement in ion fluxes from a quiet background, increasing gradually with time with a nearly flat spectrum, rising sharply near the arrival of the coronal mass ejection (CME)–driven shock, becoming nearly a power-law spectrum, then decaying exponentially afterward, with a rate that was independent of energy. From the observed fluxes, we determine diffusion coefficients, finding that far upstream of the shock the diffusion coefficients are nearly independent of energy, with a value of 1020 cm2 s−1. Near the shock, the diffusion coefficients are more than 1 order of magnitude smaller and increase nearly linearly with energy. We also determine the source of energetic particles, by comparing ratios of the intensities at the shock to estimates of the quiet-time intensity to predictions from diffusive shock acceleration theory. We conclude that the source of energetic ions is mostly the solar wind for this event. We also present potential interpretations of the near-exponential decay of the intensity behind the shock. One possibility we suggest is that the shock was overexpanding when it crossed PSP and the energetic particle intensity decreased behind the shock to fill the expanding volume. Overexpanding CMEs could well be more common closer to the Sun, and this is an example of such a case.

On the Mesoscale Structure of Coronal Mass Ejections at Mercury’s Orbit: BepiColombo and Parker Solar Probe Observations

“…Furthermore, Temmer & Bothmer (2022) estimated that the sheath density tends to overcome the ejecta density in the heliocentric distance range of 0.09-0.28 au, after which expansion of the driver generally weakens. We also note that Giacalone et al (2023) came to the same conclusion (i.e., that the 2022 February 15 CME was overexpanding by the time it impacted Parker) by observing the intensity of energetic particle increase behind the shock, possibly resulting from ions filling an expanding volume associated with the propagation of a blast wave.…”

“…First of all, we note that the abrupt magnetic field jump that we had identified as the CME-driven shock in Section 3.1 (vertical gray line in Figure 5) is indeed accompanied by a prominent rise in the solar wind bulk speed (from ∼550 to ∼850 km s −1 ), a moderate climb in the electron density and temperature, as well as an intensification of suprathermal electron fluxes (the electron flux enhancements observed prior to the shock arrival are due to the strong particle event associated with this eruption analyzed by, e.g., Giacalone et al 2023;Khoo et al 2024). The following sheath region is characterized by highly fluctuating magnetic fields, almostconstant speeds, a declining temperature profile, and a plateauing density trend except for a high-density feature close to its trailing portion.…”

Multispacecraft Observations of a Widespread Solar Energetic Particle Event on 2022 February 15–16

“…Both spacecraft observed energetic protons and electrons soon after the radio burst observation at PSP and later measured a peak enhancement of energetic protons at the shock arrival, suggesting a locally shock-accelerated proton population. A detailed analysis of the ESP event, including the source of the accelerated particles, is available in Giacalone et al (2023; see also Fraschetti & Goldberg 2023). In addition, we also noted an interesting three-slope energy spectrum near the shock, and a more involved investigation is ongoing to characterize the evolution of the energy spectrum during this event.…”

“…The ESP events observed by PSP were limited to lower-energy particles (<1 MeV; Figure 3(f)). Giacalone et al (2023) provide a detailed investigation of the ESP events observed by PSP during this event. It is important to note that the energy widths of these three proton channels are not the same for both spacecraft, and this difference is to be taken into account for cross-calibration in Appendix D. Notably, we observed the presence of an interesting three-slope spectrum with a plateau between 8 and 12 MeV near the shock (not shown here).…”

Parallel Diffusion Coefficient of Energetic Charged Particles in the Inner Heliosphere from the Turbulent Magnetic Fields Measured by Parker Solar Probe

“…On the other hand, κ ∥ from test particle simulations has shown a agreement with the predictions of QLT as noted above. Furthermore, our recent study (Giacalone et al 2023) highlights that QLT a relatively accurate estimation for κ ∥ near the CME-driven shocks. These suggest that the current work can also be helpful to the studies of SEP transport in the solar wind as well as acceleration at the interplanetary shocks.…”