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A series of solar energetic electron (SEE) events was observed from 2022 November 9 to November 15 by Solar Orbiter, STEREO-A, and near-Earth spacecraft. At least 32 SEE intensity enhancements at energies >10 keV were clearly distinguishable in Solar Orbiter particle data, with 13 of them occurring on November 11. Several of these events were accompanied by ≲10 MeV proton and ≲2 MeV nucleon ^−1 heavy-ion intensity enhancements. By combining remote-sensing and in situ data from the three viewpoints (Solar Orbiter and STEREO-A were ∼20° and ∼15° east of Earth, respectively), we determine that the origin of this rapid succession of events was a series of brightenings and jetlike eruptions detected in extreme ultraviolet (EUV) observations from the vicinity of two active regions. We find a close association between these EUV phenomena, the occurrence of hard X-ray flares, type III radio bursts, and the release of SEEs. For the most intense events, usually associated with extended EUV jets, the distance between the site of these solar eruptions and the estimated magnetic connectivity regions of each spacecraft with the Sun did not prevent the arrival of electrons at the three locations. The capability of jets to drive coronal fronts does not necessarily imply the observation of an SEE event. Two peculiar SEE events on November 9 and 14, observed only at electron energies ≲50 keV but rich in ≲1 MeV nucleon ^−1 heavy ions, originated from slow-rising confined EUV emissions, for which the process resulting in energetic particle release to interplanetary space is unclear.

The processes responsible for the acceleration of solar energetic particles (SEPs) are still not well understood, including whether SEP electrons and protons are accelerated by common or separate processes. Using a numerical particle transport model that includes both pitch-angle and perpendicular spatial diffusion, we simulate, among other quantities, the onset delay for MeV electrons and protons and compare the results to observations of SEPs from widely separated spacecraft. Such observations have previously been interpreted, in a simple scenario assuming no perpendicular diffusion, as evidence for different electron and proton sources. We show that, by assuming a common particle source together with perpendicular diffusion, we are able to simultaneously reproduce the onset delays for both electrons and protons. We argue that this points toward a common accelerator for these particles. Moreover, a relatively broad particle source is required in the model to correctly describe the observations. This is suggestive of diffusive shock acceleration occurring at large shock structures playing a significant role in the acceleration of these SEPs.

We analyze periods with elevated >40 MeV proton intensities observed near Earth over a time span of 43 yr (1973–2016) that coincide with the passage of interplanetary (IP) shocks. Typically, elevated proton intensities result from large solar energetic particle (SEP) events. The IP shocks observed during these elevated-intensity periods may or may not be related to the origin of the SEP events. By choosing those cases when the shocks can be confidently associated with the solar eruption that generated the SEP event, we analyze the components of these SEP events that are localized in the vicinity of the shock (so-called “energetic storm particles”, ESPs), focusing on those events where the ESP component exceeds 40 MeV. We examine the interdependence of these high-energy ESPs with (i) the properties of the solar eruptions that generated the shocks and the SEP events, and (ii) the parameters of the shocks at their arrival at 1 au. The solar eruptions at the origin of the shocks producing >40 MeV proton ESP intensity enhancements are within ±50° longitude of central meridian and are associated with fast coronal mass ejections (plane-of-sky speeds ≳1000 km s ^−1 ). The ESP events with the largest >40 MeV proton intensity increases tend to occur when there are structures such as intervening IP coronal mass ejections and other unrelated shocks present in the solar wind through which the shock is propagating. Among the various local shock parameters considered, only the shock speed shows a certain degree of correlation with the observed ESP intensity increase.

On 2020 April 19–20, a solar ejection was seen by spacecraft in a radial alignment that included Solar Orbiter and Wind. The ejection contained a magnetic flux rope where magnetic field and plasma parameters were well correlated between spacecraft. This structure is called an “unperturbed magnetic flux rope” (UMFR). Ahead of the UMFR is a portion of the ejection (not sheath) that is referred to as “upstream” (US). We focus on the US and inquire why the correlation is so much weaker there. Specifically, we analyze data collected by Solar Orbiter at 0.81 au and Wind at L1. We show that a plausible cause for the lack of coherence in the US is a combination of front erosion and internal reconnection occurring there. Front erosion is inferred from an analysis of azimuthal magnetic flux balance in the UMFR. In the present case, we contend that the US, rather than the UMFR, is the source of the eroded field lines. The presence of erosion is supported further by a direct comparison of the magnetic field data at both spacecraft that shows, in particular, a massive shrinkage of the front portion of the US. Internal reconnection is also happening at thin current sheets inside the US. Strong nonradial flows are reconfiguring the structure. As a result of these reconnection processes, a whole section of the US is disrupted and field lines move down the flanks of the ejection and out of view of Wind.

Large solar eruptions are often associated with long-duration γ -ray emission extending well above 100 MeV. While this phenomenon is known to be caused by high-energy ions interacting with the solar atmosphere, the underlying dominant acceleration process remains under debate. Potential mechanisms include continuous acceleration of particles trapped within large coronal loops or acceleration at coronal mass ejection (CME)-driven shocks, with subsequent back-propagation toward the Sun. As a test of the latter scenario, previous studies have explored the relationship between the inferred particle population producing the high-energy γ -rays and the population of solar energetic particles (SEPs) measured in situ. However, given the significant limitations on available observations, these estimates unavoidably rely on a number of assumptions. In an effort to better constrain theories of the γ -ray emission origin, we reexamine the calculation uncertainties and how they influence the comparison of these two proton populations. We show that, even accounting for conservative assumptions related to the γ -ray flare, SEP event, and interplanetary scattering modeling, their statistical relationship is only poorly/moderately significant. However, though the level of correlation is of interest, it does not provide conclusive evidence for or against a causal connection. The main result of this investigation is that the fraction of the shock-accelerated protons required to account for the γ -ray observations is >20%–40% for six of the 14 eruptions analyzed. Such high values argue against current CME-shock origin models, predicting a