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Abstract In this paper we examine a low-energy solar energetic particle (SEP) event observed by IS⊙IS’s Energetic Particle Instrument-Low (EPI-Lo) inside 0.18 au on 2020 September 30. This small SEP event has a very interesting time profile and ion composition. Our results show that the maximum energy and peak in intensity are observed mainly along the open radial magnetic field. The event shows velocity dispersion, and strong particle anisotropies are observed throughout the event, showing that more particles are streaming outward from the Sun. We do not see a shock in the in situ plasma or magnetic field data throughout the event. Heavy ions, such as O and Fe, were detected in addition to protons and 4He, but without significant enhancements in 3He or energetic electrons. Our analysis shows that this event is associated with a slow streamer blowout coronal mass ejection (SBO-CME), and the signatures of this small CME event are consistent with those typical of larger CME events. The time–intensity profile of this event shows that the Parker Solar Probe encountered the western flank of the SBO-CME. The anisotropic and dispersive nature of this event in a shockless local plasma gives indications that these particles are most likely accelerated remotely near the Sun by a weak shock or compression wave ahead of the SBO-CME. This event may represent direct observations of the source of the low-energy SEP seed particle population. 

Energetic electron flux enhancements for 100s keV energies are often observed at lowLshells (L < 4) in the inner magnetosphere during geomagnetic storms. However, protons with similar energies do not penetrate as deeply as electrons. Electric fields from subauroral polarization streams (SAPS) have been proposed as a mechanism to explain the difference between the 100s keV electron and proton behavior by altering the particles’ drift paths and allowing electrons to access lowerLshells than protons. Although the primary signature of SAPS is a strong radial electric field, there are corresponding westward/eastward azimuthal electric fields on the eastern/western regions of the SAPS that cause inward/outward radial transport and a differential response between the oppositely drifting electrons and protons. We examine three events where SAPS were observed by the Van Allen Probes near the same time andLshell range as 100s keV electron enhancements deep within the inner magnetosphere. The observations demonstrate that 100s keV electrons were progressively transported radially inward and trapped at lowLshells that were consistent with the spatial extent of the SAPS electric fields. Proton flux enhancements were limited to <100 keV energies and were only observed temporarily in the SAPS region, indicating that these particles were on open drift paths. The particle observations are consistent with the differential drift paths for electrons and protons predicted by a simple SAPS electric field model, suggesting that SAPS play an important role in 100s keV particle dynamics at lowLshells in the inner magnetosphere.

 

Abstract We present observations of ≳10–100 keV nucleon −1 suprathermal (ST) H, He, O, and Fe ions associated with crossings of the heliospheric current sheet (HCS) at radial distances of <0.1 au from the Sun. Our key findings are as follows: (1) very few heavy ions are detected during the first full crossing, the heavy-ion intensities are reduced during the second partial crossing and peak just after the second crossing; (2) ion arrival times exhibit no velocity dispersion; (3) He pitch-angle distributions track the magnetic field polarity reversal and show up to ∼10:1 anti-sunward, field-aligned flows and beams closer to the HCS that become nearly isotropic farther from the HCS; (4) the He spectrum steepens either side of the HCS, and the He, O, and Fe spectra exhibit power laws of the form ∼ E −4 – E 6 ; and (5) maximum energies E X increase with the ion’s charge-to-mass ( Q / M ) ratio as E X / E H ∝ ( Q X / M X ) δ , where δ ∼ 0.65–0.76, assuming that the average Q states are similar to those measured in gradual and impulsive solar energetic particle events at 1 au. The absence of velocity dispersion in combination with strong field-aligned anisotropies closer to the HCS appears to rule out solar flares and near-Sun coronal-mass-ejection-driven shocks. These new observations present challenges not only for mechanisms that employ direct parallel electric fields and organize maximum energies according to E / Q but also for local diffusive and magnetic-reconnection-driven acceleration models. Reevaluation of our current understanding of the production and transport of energetic ions is necessary to understand this near-solar, current-sheet-associated population of ST ions. 

Ion transport from the plasma sheet to the ring current is the main cause of the development of the ring current. Energetic (>150 keV) ring current ions are known to be transported diffusively in several days. A recent study suggested that energetic oxygen ions are transported closer to the Earth than protons due to the diffusive transport caused by a combination of the drift and drift‐bounce resonances with Pc 3–5 ultralow frequency waves during the 24 April 2013 magnetic storm. To understand the occurrence conditions of such selective oxygen increase (SOI), we investigate the phase space densities (PSDs) between protons and oxygen ions with the first adiabatic invariants (μ) of 0.1–2.0 keV/nT measured by the Radiation Belt Storm Probes Ion Composition Experiment instrument on the Van Allen Probes atL ~ 3–6 during 90 magnetic storms in 2013–2017. We identified the SOI events in which oxygen PSDs increase while proton PSDs do not increase during a period of ~9 hr (one orbital period). Among the 90 magnetic storms, 33% were accompanied by the SOI events. Global enhancements of Pc 4 and Pc 5 waves observed by ground magnetometers during the SOI events suggest that radial transport due to combination of the drift‐bounce resonance with Pc 4 oscillations and the drift resonance with Pc 5 oscillations can be the cause of SOIs. The contribution of the SOI events to the magnetic storm intensity is roughly estimated to be ~9% on average.

 

Saturn's magnetosphere has been extensively studied over the past 13 years with the now retired Cassini mission. Periodic modulations in a variety of magnetospheric phenomena have been observed at periods close to those associated with the emission intensity of Saturn kilometric radiation (SKR). Resulting from Rayleigh‐Taylor like plasma instabilities, interchange is believed to be the main plasma transport process in Saturn's inner to middle magnetosphere. Here we examine the organization of equatorially observed interchange events identified based on high‐energy (3–22 keV) H⁺intensifications by several longitude systems that have been derived from different types of measurements. The main question of interest here is as follows: Do interchange injections undergo periodicities similar to the Saturn kilometric radiation or other magnetospheric phenomena? We find that interchange shows enhanced occurrence rates in the northern longitude systems between 30° and 120°, particularly between 7 and 9 Saturn Radii. However, this modulation is small compared to the organization by local time. Additionally, this organization is weak and inconsistent with previous findings based on data with a limited time span.