SEP Events Research Articles

Electrostatic charging of the sunlit hemisphere of the Moon under different plasma conditions

Accounting for the continuous interaction of the solar radiation, the development of electrostatic charge on the sunlit lunar regolith under extreme plasma conditions has been investigated—the ambient plasma around Moon corresponds to the plasma parameters associated with the solar wind, wake region, SEP events, and terrestrial magnetosphere. The photoemission of electrons from the lunar surface corresponding to the solar radiation spectrum, electron energy-dependent secondary electron emission and simultaneous collection of the ambient non-Maxwellian plasma electrons/ions have been considered the dominant charging mechanisms. The lunar surface potential has been derived using the dynamical balance of the photoemission and plasma accretion currents over its surface—the potential dependence of the charging currents has consistently been accounted for. In results, the lunar surface potential dependence on the plasma, surface, and radiation parameters have been parametrically derived. For the high temperature plasma composition, the sunlit locations over the lunar surface are predicted to acquire a negative potential. The outcome infers that depending on topography and location along with realistic plasma/surface parameters, the lunar surface may hold significant contrast in charging, and it may differ by the orders of magnitude. Such disparity in the surface charging may act as a source of the transport of charged dust and local atmospheric charge (ions/electrons) over the lunar regolith.

Source of Energetic Protons in the 2014 September 1 Sustained Gamma-ray Emission Event

We report on the source of {>},300~mbox{MeV} protons during the SOL2014-09-01 sustained gamma-ray emission (SGRE) event based on multi-wavelength data from a wide array of space- and ground-based instruments. Based on the eruption geometry we provide concrete explanation for the spatially and temporally extended gamma -ray emission from the eruption. We show that the associated flux rope is of low inclination (roughly oriented in the east–west direction), which enables the associated shock to extend to the frontside. We compare the centroid of the SGRE source with the location of the flux rope’s leg to infer that the high-energy protons must be precipitating between the flux rope leg and the shock front. The durations of the SOL2014-09-01 SGRE event and the type II radio burst agree with the linear relationship between these parameters obtained for other SGRE events with duration geq 3~mbox{hrs}. The fluence spectrum of the SEP event is very hard, indicating the presence of high-energy (GeV) particles in this event. This is further confirmed by the presence of an energetic coronal mass ejection with a speed {>},2000~mbox{km},mbox{s}^{-1}, similar to those in ground level enhancement (GLE) events. The type II radio burst had emission components from metric to kilometric wavelengths as in events associated with GLE events. All these factors indicate that the high-energy particles from the shock were in sufficient numbers needed for the production of gamma -rays via neutral pion decay.

From Sun to Interplanetary Space: What is the Pathlength of Solar Energetic Particles?

Abstract Solar energetic particles (SEPs), accelerated during solar eruptions, propagate in turbulent solar wind before being observed with in situ instruments. In order to interpret their origin through comparison with remote sensing observations of the solar eruption, we thus must deconvolve the transport effects due to the turbulent magnetic fields from the SEP observations. Recent research suggests that the SEP propagation is guided by the turbulent meandering of the magnetic fieldlines across the mean magnetic field. However, the lengthening of the distance the SEPs travel, due to the fieldline meandering, has so far not been included in SEP event analysis. This omission can cause significant errors in estimation of the release times of SEPs at the Sun. We investigate the distance traveled by the SEPs by considering them to propagate along fieldlines that meander around closed magnetic islands that are inherent in turbulent plasma. We introduce a fieldline random walk model which takes into account the physical scales associated to the magnetic islands. Our method remedies the problem of the diffusion equation resulting in unrealistically short pathlengths, and the fractal dependence of the pathlength of random walk on the length of the random-walk step. We find that the pathlength from the Sun to 1 au can be below the nominal Parker spiral length for SEP events taking place at solar longitudes 45E to 60W, whereas the western and behind-the-limb particles can experience pathlengths longer than 2 au due to fieldline meandering.

Are Solar Energetic Particle Events and Type II Bursts Associated with Fast and Narrow Coronal Mass Ejections?

Gradual solar energetic ( $E >10~\mbox{MeV}$ ) particle (SEP) events and metric through kilometric wavelength type II radio bursts are usually associated with shocks driven by fast ( $V \geq 900~\mbox{km}\,\mbox{s}^{-1}$ ) and wide ( $W \geq 60^{\circ} $ ) coronal mass ejections (FW CMEs). This criterion was established empirically by several studies from solar cycle 23. The characteristic Alfven speed in the corona, which ranges over 500 – 1500 km s−1 at heights ${\geq}\, 2~R_{\text{o}}$ , provides the minimum $V$ requirement for a CME to drive a shock, but the general absence of SEP events or type II bursts with fast and narrow ( $W < 60^{\circ}$ ) CMEs has not been explained. We review and confirm the earlier studies with a more comprehensive comparison of SEP events and type II bursts with fast and narrow (FN) CMEs. We offer an explanation for the lack of SEP event and type II burst associations with FN CMEs in terms of recent heuristic arguments and modeling that show that the response of a magnetized plasma to the propagation of a CME depends on the CME geometry as well as on its speed. A clear distinction is made between a projectile that propagates through the medium to produce a bow shock, and a 3D piston that everywhere accumulates material to produce a broad shock and sheath. The bow shock is unfavorable for producing SEP events and type II bursts, but the $60^{\circ} $ cut-off is not explained.

Prediction Model for Solar Energetic Proton Events: Analysis and Verification

AbstractSolar energetic protons (SEPs) can cause radiation damage to satellites. The Space Environment Prediction Center of China defines the start of a SEP event as the time when three consecutive instances of the 5‐min‐averaged integral flux of &gt;10 MeV protons equal or exceed the 10 proton flux unit threshold. In this study, we analyzed the 5‐min‐averaged soft X‐ray flux and the differential and integral proton flux obtained by the Geostationary Operational Environmental Satellites for the period from January 1990 to September 2017 and developed SEP prediction models and their products. The statistical models take one or two data products and the given thresholds as the predictor and predict whether a SEP event will occur or not in the next 24 hr. The quality of the forecast models was measured by comparing the model results against certain verification metrics. Our model taking the products of 5‐min‐averaged integral flux of &gt;10 MeV protons and long wavelength of soft X‐ray flux as predictors can provide a probability of detection of 0.80 (152/190), a false alarm ratio of 0.26 (53/205), and an average warning time of 2.6 hr for the correctly predicted events. In addition, the model can provide a critical success index of 0.63, a Gilbert skill score of 0.62, and a Heidke skill score of 0.76.

The CubeSat Mission to Study Solar Particles

The CubeSat Mission for studying Solar Particles is a NASA Science Mission Directorate and Heliophysics Division funded 6U Interplanetary CubeSat Science Mission. CuSP is scheduled to launch in mid-2020 as a secondary payload on the SLS EM -1 (Exploratory Mission One) flight. CuSP is a pathfinder mission for Space Weather Research as it will be the first heliophysics science mission to be placed in heliocentric orbit outside the influence of the Earth's magnetosphere. CuSP features three complementary, miniaturized sensors to address two science objectives: study the sources and acceleration mechanisms of solar and IP particles in near-Earth orbit, and support space weather research by determining proton radiation levels during SEP events and identifying properties of ST ions that could help predict the arrival of strong CME-driven IP shock waves that produce geomagnetic storms.

Onset Time of the GLE 72 Observed at Neutron Monitors and its Relation to Electromagnetic Emissions

We present an overview of the ground-level enhancement (GLE 72) of the cosmic-ray intensity associated with the recent powerful solar flare SOL2017-09-10 (X-ray class X8.9) based on the available neutron monitor (NM) network observations and on data from the satellite GOES 13. The maximum increase at high-latitude near-sea-level NMs was ${\approx }\,6\,\mbox{--}\,7\%$ (2-min averages), greater with better time resolution. A scatter plot of the maximum increase of the GLE versus solar energetic-particle (SEP, proton) flux ${>}\,100~\mbox{MeV}$ shows one of the softest spectra among GLEs relative to the SEP fluxes. However, at two high-mountain middle-latitude NMs the increase was ${\approx }\,1\%$ , indicating the possibility of proton acceleration up to 6 GeV. Among the analyzed NM data the Fort Smith (FSMT) NM shows the earliest and the rather high increase between 16:06 – 16:08 UT. This indicates an anisotropy in the first phase of the GLE event. We calculate the acceptance cones of several NM stations at high latitudes and contours of pitch angles corresponding to the interplanetary magnetic field (IMF). When employing the available data we find that pion-decay $\gamma $ -ray emission onset is in accordance with the time of the main flare energy release. The observed time interval of the impulsive burst of ${>}\,100~\mbox{MeV}$ $\gamma $ -ray emission probably corresponds to the time of a turbulent current sheet creation. The observed location of the impulsive burst pion-decay emission source coincides with the active region and the cusp-shaped structure. It seems that models assuming sub-relativistic proton production beginning in a turbulent reconnecting current sheet are consistent with the observations. If these particles were released from the Sun during a type III emission with a pion-decay maximum at $16{:}00{:}30\pm 30~\mbox{UT}$ , we get a plausible path length equal to $1.5\pm 0.3~\mbox{AU}$ of the particles responsible for the onset of the SEP event and GLE. The time lag of GLE 72 corresponds to the most probable interval of the time difference between GLE onset and main flare energy release. Although other scenarios are not excluded we attribute the protons that create the pion-decay emission and the protons responsible for the GLE and SEP event onset to a general population of accelerated particles.

A study on radio-loud interacting/non-interacting CMEs-associated SEPs and solar flares

We have established a data set of 58 major hybrid SEP events associated with meter-to-decahectometer wavelength (m-to-DH) type II bursts, solar flares, and radio-load CMEs during the period of 1997–2014. The main focus of our study is to address the following two questions: Does the interaction of CMEs play a role in the enhancement of SEP intensity? Is there any difference in the seed population, and parent eruptions in the SEP events with and without CME interactions? Hence, the sample of 58 events is classified into two sets: (i) 35 non-interacting-CME-associated SEP events; (ii) 23 interacting-CME-associated SEP events. All the characteristics of SEPs, their associated CMEs/flares and the relationships between them are statistically analyzed and compared. Some of the basic attributes and relative elemental abundances (Fe/O ratios) of the both the sets are also compared. The results indicate that the seed particles in non-interacting-CME-associated SEP events are mostly from solar wind/coronal materials. But in the case of interacting-CME-associated SEP events, it may be associated with both flare material from preceding flares and coronal materials from solar wind/preceding CMEs. The correlation studies reveal that there are clear correlations between logarithmic peak intensity of SEP events and properties of CMEs (space speed: cc = 0.56) and solar flares (peak intensity: cc = 0.40; integrated flux: cc = 0.52) for non-interacting-CME-associated SEP events. But these correlations are absent for the interacting-CME-associated events. In addition, the results suggest that interaction of primary CMEs with their preceding CMEs plays an important role in the enhancement of peak intensity of SEPs at least for a set of m-to-DH type II bursts associated SEP events.

Is the enhancement of type II radio bursts during CME interactions related to the associated solar energetic particle event?

We investigated 64 pairs of interacting-CME events identified from simultaneous observations by the SOHO and STEREO spacecraft from January 2010 to August 2014, to examine the relationship between large SEP events in the energy range of ∼25 to ∼60MeV and properties of the interacting CMEs. We found that during CME interactions, the large SEP events in this study were all generated by CMEs with the presence of enhanced type II radio bursts, which also have wider longitudinal distributions compared to events without a type II radio burst or its enhancement (almost always associated with small SEP events). It seems that the signature of type II radio burst enhancement is a good discriminator between large SEP and small or no SEP event producers during CME interactions. The type II radio burst enhancement is more likely to be generated by CME interactions, with the main CME having a larger speed (v), angular width (WD), mass (m) and kinetic energy (Ek), and taking over the preceding CMEs. The preceding CMEs in these instances have higher v, WD, m and Ek than those in CME pairs missing type II radio bursts or enhancements. Generally, the values of these properties in the type-II-enhanced events are typically higher than the corresponding non-type-II or non-type-II-enhanced cases for both the main and preceding CMEs. Our analysis also revealed that the intensities of associated SEP events correlate negatively with the intersection height of the two CMEs. Moreover, the overlap width of two CMEs is typically larger in type-II-enhanced events than in non-type-II or non-type-II-enhanced events. Most type-II-enhanced events and SEP events are coincident and are almost always made by the fast and wide main CMEs that sweep fully over relatively slower and narrower preceding CMEs. We suggest that a fast CME with enough energy completely overtaking a relatively narrower preceding CME, especially at low height, can drive a more energetic shock signified by the enhanced type II radio bursts. The shock may accelerate ambient particles (likely provided by the preceding CME) and lead to large SEP events more easily.

Statistical analysis of shock properties driven by coronal mass ejections based on observations of type II radio bursts

In this paper, we investigate 77 type-II radio burst events' data observed by Wind/WAVES and STEREO/SWAVES from January 2007 to December 2015. By fitting the frequency-time profile to obtain the corresponding shock velocity, we study the relationship between the parameters of shock and those of coronal mass ejection (CME), solar flare and the associated SEP events, and explore the influences of type II radio enhancement on these relationships. Our findings are as follows. 1) In general, at the onset time of type II radio bursts within deca-hectometric (DH) waveband, the shock front is about 0.4Rs ahead of the leading edge of CME (shock standoff distance), and this distance increases as the CME propagates outward. In the low and high corona, the relationship between shock standoff distance and CME speed indicates a significant difference; the shock standoff distance is correlated with the CME speed positively at the low altitude, but negatively at high altitude. 2) The CME speed of the events with radio enhancement is significantly larger than that with no radio enhancement; and comparing with the events with no radio enhancement, the correlation coefficient between the shock speed and the mass and kinetic energy of the associated CME is significantly high for the events with radio enhancement. 3) There is no correlation between the duration of type II radio burst in DH waveband with enhancement and the speed, mass and kinetic energy of CME. However, it presents a positive correlation for the events with no radio enhancement. 4) Usually the speed of shock that can produce SEP event is obviously higher than that with producing no SEP event. The probability of the SEP generated by the events associated with radio enhancement is slightly higher than with no radio enhancement (73.5% &gt; 67.4%), but for the large SEP events, the generation probability (67.6%) associated with radio enhancement is about one-order of magnitude higher than that with no radio enhancement (37.2%). This conclusion indicates that the type II radio enhancement can be used as one of the signatures of the shock or the radio source that more probably produces a large SEP event.

Ionospheric Response Observed by EISCAT During the 6–8 September 2017 Space Weather Event: Overview

AbstractWe present ionospheric plasma conditions observed by the EISCAT radars in Tromsø and on Svalbard, covering 68°–81° geomagnetic latitude, during 6–8 September 2017. This is a period when X2.2 and X9.3 X‐ray flares occurred, two interplanetary coronal mass ejections (ICMEs) arrived at the Earth accompanied by enhancements of MeV‐range energetic particle flux in both the solar wind (SEP event) and inner magnetosphere, and an AL &lt; −2,000 substorm took place. (1) Both X flares caused enhancement of ionospheric electron density for about 10 min. The X9.3 flare also increased temperatures of both electrons and ions over 69°–75° geomagnetic latitude until the X‐ray flux decreased below the level of X‐class flares. However, the temperature was not enhanced after the previous X2.2 flare in the prenoon sector. (2) At around 75° geomagnetic latitude, the prenoon ion upflow flux slightly increased the day after the X9.3 flare, which is also after the first ICME and a SEP event, while no outstanding enhancement was found at the time of these X flares. (3) The upflow velocity sometimes decreased when the interplanetary magnetic field (IMF) turned southward. (4) Before the first ICME arrival after the SEP event under weak IMF with Bz ~0 nT, a substorm‐like expansion of the auroral arc signature took place without local geomagnetic signature near local midnight, while no notable change was observed after the ICME arrival. (5) AL reached &lt;−2,000 nT only after the arrival of the second ICME with strongly southward IMF. Causality connections between the solar/solar wind event and the ionospheric responses remain unclear.

Toward a Quantitative Model for Simulation and Forecast of Solar Energetic Particle Production during Gradual Events. I. Magnetohydrodynamic Background Coupled to the SEP Model

Abstract Solar energetic particles (SEPs) are an important aspect of space weather. SEP events possess a high destructive potential, since they may cause disruptions of communication systems on Earth and be fatal to crew members on board spacecraft and, in extreme cases, harmful to people on board high-altitude flights. However, currently the research community lacks efficient tools to predict such a hazardous threat and its potential impacts. Such a tool is a first step for mankind to improve its preparedness for SEP events and ultimately to be able to mitigate their effects. The main goal of the presented research effort is to develop a computational tool that will have the forecasting capability and can serve as an operational system that will provide live information on the current potential threats posed by SEP based on the observations of the Sun. In the present paper we discuss the fundamentals of magnetohydrodynamical simulations to be employed as a critical part of the desired forecasting system.

The September 2017 SEP Event in Context With the Current Solar Cycle: Mars Express ASPERA‐3/IMA and MAVEN/SEP Observations

AbstractWe use Mars Atmosphere and Volatile Evolution/Solar Energetic Particle (MAVEN/SEP) data to estimate the ranges of particle energies that generate background noise in the Analyzer of Space Plasmas and Energetic Atoms‐3/Ion Mass Analyzer (IMA) instrument on Mars Express. The particles that generate IMA background counts are estimated to be electrons with energies &gt;1 MeV and protons &gt;20 MeV. The September 2017 event at Mars resulted in the strongest flux of energetic particles measured by MAVEN/SEP. We correspondingly use the IMA background data to compare this event with the rest of the last solar cycle and back to 2004, finding the event to be the fourth strongest solar energetic particle event detected by Mars Express.

Sea-Effect Precipitation over the Shandong Peninsula, Northern China

AbstractSea-effect precipitation (SEP) over the Shandong Peninsula is a unique climatological phenomenon in mainland China, and it exerts a considerable impact on the southern shore of the Bohai Sea. From observed data from 123 stations for the period 1962–2012, the characteristics of cold-season (November–February) SEP in this area were analyzed. Results showed that SEP occurred throughout the late autumn and winter. In all, 1173 SEP days were identified during the 51 years, of which snow days accounted for 73.7% and rain and snow–rain days accounted for 16.1% and 10.1%, respectively. December had the largest number of SEP snow days, followed by January and November. November was the most productive month in terms of SEP rain and snow–rain days. Intense SEP snowfall mainly affected the inland hill area of the peninsula, whereas light SEP snowfall reached farther inland. SEP rainfall shared a similar pattern with snowfall. The SEP frequency showed a significant interannual variability and a nonsignificant upward trend over the period analyzed. SEP was most likely to occur when the temperature difference between sea surface and 850 hPa over the Bohai Sea was above 10°C, indicating a dominant influence of low-level cold-air advection over the sea on the generation and development of the weather phenomenon. A significant negative correlation was also found between the area of sea ice in the Bohai Sea and intense SEP snowfall, indicating that sea ice extent had an important effect on SEP variability over the peninsula. In the case of extremely intense SEP events, a deeper East Asian trough at the 500-hPa level developed over the southwest of the study area and temperature and geopotential height contours were orthogonal to each other, indicating strong geostrophic cold-air advection over the Bohai Sea and the Shandong Peninsula. The extremely intense SEP events were also characterized by anomalous low temperature and high relative humidity in the lower troposphere, which contributed to greater gravitational instability in the study area.

Modeling a Single SEP Event from Multiple Vantage Points Using the iPATH Model

Abstract Using the recently extended 2D improved Particle Acceleration and Transport in the Heliosphere (iPATH) model, we model an example gradual solar energetic particle event as observed at multiple locations. Protons and ions that are energized via the diffusive shock acceleration mechanism are followed at a 2D coronal mass ejection-driven shock where the shock geometry varies across the shock front. The subsequent transport of energetic particles, including cross-field diffusion, is modeled by a Monte Carlo code that is based on a stochastic differential equation method. Time intensity profiles and particle spectra at multiple locations and different radial distances, separated in longitudes, are presented. The results shown here are relevant to the upcoming Parker Solar Probe mission.

Magnetospheric access for solar protons during the January 2005 SEP event

The early phase of the extraordinary solar energetic particle 20 January, 2005 event having the highest peak flux of any SEP in the past 50 years of protons with energies &gt; 100 MeV is studied. Solar energetic particles (&gt;16 MeV) entry to the Earth’s magnetosphere on January 20, 2005 under northward interplanetary magnetic field conditions is considered based on multi-satellite data analysis and magnetic field simulation. Solar wind parameters and interplanetary magnetic field data, as well as calculations in terms of the A2000 magnetospheric magnetic field model were used to specify conditions in the Earth’s environment corresponding to solar proton event. It was shown that during the early phase of the event energetic particle penetration into the magnetosphere took place in the regions on the magnetopause where the magnetospheric and interplanetary magnetic field vectors are parallel. Complex analysis of the experimental data on particle fluxes in the interplanetary medium (data from ACE spacecraft) and on low-altitude (POES) and geosynchronous (GOES) orbits inside the Earth’s magnetosphere show two regions on the magnetopause responsible for particle access to the magnetosphere: the near equatorial day-side region and open field lines window at the high-latitude magnetospheric boundary. Calculations in terms of A2000 magnetospheric magnetic field model and comparison with SuperDARN images support the link between high-latitude solar energetic particle precipitations and the region at the magnetopause where the magnetospheric field is coupled with northward IMF, allowing solar particles entrance into the magnetosphere and access to the northern polar cap.

Solar flares, CMEs and solar energetic particle events during solar cycle 24

We present here a study of Solar Energetic Particle Events (SEPs) associated with solar flares during 2010–2014 in solar cycle 24. We have selected the flare events (≥GOES M-class), which produced SEPs. The SEPs are classified into three categories i.e. weak (proton intensity ≤ 1 pfu), minor (1 pfu < proton intensity < 10 pfu) and major (proton intensity ≥ 10 pfu). We used the GOES data for the SEP events which have intensity greater than one pfu and SOHO/ERNE data for the SEP event less than one pfu intensity. In addition to the flare and SEP properties, we have also discussed different properties of associated CMEs.

Flare magnetic reconnection fluxes as possible signatures of flare contributions to gradual SEP events

The primary sources of solar energetic (E > 20 MeV) particle (SEP) events are flares and CME-driven shocks. Some studies claim that even up to GeV energies solar flares are major contributors to SEP events. There are several candidate flare processes for producing SEPs, but acceleration in magnetic reconnection regions is probably the most efficient. Previous studies have relied on flare radiation signatures to determine the times and locations of SEP injections. An alternative approach is to use the amount of magnetic flux that gets reconnected during solar flares. The photospheric magnetic flux swept out by flare ribbons is thought to be directly related to the amount of magnetic reconnection in the corona and is therefore a key diagnostic tool for understanding the physical processes in flares and CMEs. We use the database of flare magnetic reconnection fluxes to compare these parameters with peak intensities of SEP events. We find that while sizes of 15 ∼25-MeV SEP events in the western hemisphere correlate with both CME speeds and reconnection fluxes, there are many cases of large reconnection fluxes with no observed SEP events. The occurrence of large reconnection fluxes accompanied by slow CMEs but no SEP events suggests that the CME shocks are the primary, if not the only, sources of high energy (E > 100 MeV) SEP events.

Modeling solar energetic particle events using ENLIL heliosphere simulations

AbstractSolar energetic particle (SEP) event modeling has gained renewed attention in part because of the availability of a decade of multipoint measurements from STEREO and L1 spacecraft at 1 AU. These observations are coupled with improving simulations of the geometry and strength of heliospheric shocks obtained by using coronagraph images to send erupted material into realistic solar wind backgrounds. The STEREO and ACE measurements in particular have highlighted the sometimes surprisingly widespread nature of SEP events. It is thus an opportune time for testing SEP models, which typically focus on protons ~1–100 MeV, toward both physical insight to these observations and potentially useful space radiation environment forecasting tools. Some approaches emphasize the concept of particle acceleration and propagation from close to the Sun, while others emphasize the local field line connection to a traveling, evolving shock source. Among the latter is the previously introduced SEPMOD treatment, based on the widely accessible and well‐exercised WSA‐ENLIL‐cone model. SEPMOD produces SEP proton time profiles at any location within the ENLIL domain. Here we demonstrate a SEPMOD version that accommodates multiple, concurrent shock sources occurring over periods of several weeks. The results illustrate the importance of considering longer‐duration time periods and multiple CME contributions in analyzing, modeling, and forecasting SEP events.

Re-Acceleration of Energetic Particles in Large-Scale Heliospheric Magnetic Cavities

AbstractCase studies show that some energetic particle flux enhancements up to MeV/nuc. observed at 1 AU cannot be treated as a consequence of particle acceleration at shocks or during flares. Atypical energetic particle events (AEPEs) are often detected during crossings of magnetic cavities formed by strong current sheets of various origins in the solar wind. Such cavities confine small-scale magnetic islands (SMIs) produced by magnetic reconnection. SMIs, in turn, trap and re-accelerate energetic particles according to predictions based on the theory of Zank et al. describing stochastic particle energization in the supersonic solar wind via numerous dynamically interacting SMIs. AEPEs possess energies that overlap SEP events and can be an important component in understanding space weather.