Energetic Particle Fluxes Research Articles

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 >1 MeV and protons >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.

Constraining the stellar energetic particle flux in young solar-like stars

AbstractAnomalies in the abundance measurements of short lived radionuclides in meteorites indicate that the protosolar nebulae was irradiated by a large number of energetic particles (E≳ 10 MeV), often called solar cosmic rays. The particle flux of the contemporary Sun cannot explain these anomalies, but, similar to T Tauri stars, the young Sun was more active and probably produced enough high energy particles. However, the stellar particle (SP) flux of young stars is essentially unknown. We model the impact of high-energy ionization sources on the chemistry of the circumstellar environment (disks and envelopes). The model includes X-ray radiative transfer and makes use of particle transport models to calculate the individual molecular hydrogen ionization rates. We study the impact on the chemistry via the ionization tracers HCO+ and N2H+. We argue that spatially resolved observations of those molecules combined with detailed models allow for disentangling the contribution of the individual high-energy ionization sources and to put constraints on the SP flux in young stars.

High early solar activity inferred from helium and neon excesses in the oldest meteorite inclusions

Astronomical observations show that early in their evolution, stars experience stages of high activity associated with enhanced energetic particle fluxes1. The Sun’s early activity is often inferred from the spallogenic isotope record (for example, 10Be) in the Solar System’s oldest materials2, calcium–aluminium-rich inclusions (CAIs) in meteorites3,4. However, the 10Be record could be affected by processes other than in situ irradiation by solar particles5. Noble gases can give less ambiguous insights because they are inert volatiles and hence not incorporated into CAIs during their formation6. Here we show that hibonite-rich CAIs, considered to have formed before 26Al-rich CAIs7,8, contain helium and neon excesses that can be unambiguously attributed to in situ irradiation by energetic particles. Given their volatile nature, we infer that the noble gases were produced by irradiation in a relatively cold region at a considerable distance from the Sun (not at the inner disk edge), requiring high particle fluxes and thus high early solar activity. Because more evolved CAIs lack comparable noble gas irradiation records9, we conclude that the oldest Solar System materials experienced a phase of intense irradiation not recorded by materials that formed later. Consequently, disk properties or energetic particle fluxes changed significantly during the very early phases of Solar System evolution. Noble gas abundances measured in the oldest calcium–aluminium-rich inclusions (CAIs) reveal a burst of intense solar irradiation early in the Solar System’s history, not recorded by CAIs that formed later. This result is consistent with a T Tauri phase for the Sun.

Using Extreme Value Theory for Determining the Probability of Carrington‐Like Solar Flares

AbstractBy their very nature, extreme space weather events occur rarely, and therefore, statistical methods are required to determine the probability of their occurrence. Space weather events can be characterized by a number of natural phenomena such as X‐ray (solar) flares, solar energetic particle fluxes, coronal mass ejections, and various geophysical indices (such as Dst, Kp, and F10.7). In this paper extreme value theory (EVT) is used to investigate the probability of extreme solar flares. Previous work has assumed that the distribution of solar flares follows a power law. However, such an approach can lead to a poor estimation of the return times of flares due to uncertainties in the tails of the probability distribution function. Using EVT and Geostationary Operational Environmental Satellites X‐ray flux data, it is shown that the expected 150 year return level is approximately an X60 flare while a Carrington‐like flare is a one in a 100 year event. In the worst case the 150 year return level is an X90 flare while a Carrington flare is a one in 30 year event. It is also shown that the EVT results are consistent with flare data from the Kepler space telescope mission.

Interpretation of increased energetic particle flux measurements by SEPT aboard the STEREO spacecraft and contamination

Context. Interplanetary (IP) shocks are known to be accelerators of energetic charged particles observed in-situ in the heliosphere. However, the acceleration of near-relativistic electrons by shocks in the interplanetary medium is often questioned. On 9 August 2011 a corotating interaction region (CIR) passed STEREO B (STB), which resulted in a flux increase in the electron and ion channels of the Solar Electron and Proton Telescope (SEPT). Because electron measurements in the few keV to several 100 keV range rely on the so-called magnet foil technique, which is utilized by SEPT, ions can contribute to the electron channels. Aim. We aim to investigate whether the flux increase in the electron channels of SEPT during the CIR event on 9 August 2011 is caused by ion contamination only. Methods. We compute the SEPT response functions for protons and helium utilizing an updated GEANT4 model of SEPT. The CIR energetic particle ion spectra for protons and helium are assumed to follow a Band function in energy per nucleon with a constant helium to proton ratio. Results. Our analysis leads to a helium to proton ratio of 16.9% and a proton flux following a Band function with the parameters I0 = 1.24 × 104 (cm2 s sr MeV nuc−1)−1, Ec = 79 keV nuc−1, and spectral indices of γ1 = −0.94 and γ2 = −3.80, which are in good agreement with measurements by the Suprathermal Ion Telescope (SIT) aboard STB. Conclusions. Since our results explain the SEPT measurements, we conclude that no significant amount of electrons were accelerated between 55 and 425 keV by the CIR.

Analysis of Dark Current in BRITE Nanostellite CCD Sensors

The BRightest Target Explorer (BRITE) is the pioneering nanosatellite mission dedicated for photometric observations of the brightest stars in the sky. The BRITE charge coupled device (CCD) sensors are poorly shielded against extensive flux of energetic particles which constantly induce defects in the silicon lattice. In this paper we investigate the temporal evolution of the generation of the dark current in the BRITE CCDs over almost four years after launch. Utilizing several steps of image processing and employing normalization of the results, it was possible to obtain useful information about the progress of thermal activity in the sensors. The outcomes show a clear and consistent linear increase of induced damage despite the fact that only about 0.14% of CCD pixels were probed. By performing the analysis of temperature dependencies of the dark current, we identified the observed defects as phosphorus-vacancy (PV) pairs, which are common in proton irradiated CCD matrices. Moreover, the Meyer-Neldel empirical rule was confirmed in our dark current data, yielding meV for proton-induced PV defects.

Preliminary results of the High Energetic Particle Package on-board the China Seismo-Electromagnetic Satellite

The high energetic particle package (HEPP) on-board the China Seismo-Electromagnetic Satellite (CSES) was launched on February 2, 2018. This package includes three independent detectors: HEPP-H, HEPP-L, and HEPP-X. HEPP-H and HEPP-L can detect energetic electrons from 100 keV to approximately 50 MeV and protons from 2 MeV to approximately 200 MeV. HEPP-X can measure solar X-rays in the energy range from 1 keV to approximately 20 keV. The objective of the HEPP payload was to provide a survey of energetic particles with high energy, pitch angle, and time resolutions in order to gain new insight into the space radiation environments of the near-Earth system. Particularly, the HEPP can provide new measurements of the magnetic storm related precipitation of electrons in the slot region, and the dynamics of radiation belts. In this paper, the HEPP scientific data sets are described and initial results are provided. The scientific data can show variations in the flux of energetic particles during magnetic storms.

The first joint experimental results between SURA and CSES

In June 2018, for the first time, the SURA heating facility in Russia , together with the in-orbit China Seismo-Electromagnetic Satellite (CSES), carried out a series of experiments in emitting high frequency (HF) O-mode radio waves to disturb the ionosphere. This paper reports data from those experiments, collected onboard CSES, including electric field, in-situ plasma parameters, and energetic particle flux. Five cases are analyzed, two cases in local daytime and three in local nighttime. We find that the pumping wave frequencies f0 in local daytime were close to the critical frequency of the F2 layer foF2, but no pumping waves were detected by the electric field detector (EFD) on CSES even when the emitted power reached 90 MW, and no obvious plasma disturbances were observed from CSES in those two daytime cases. But on June 16, there existed a spread F phenomena when f0 was lower than foF2 at that local daytime period. During the three cases in local nighttime, the pumping waves were clearly distinguished in the HF-band electric field at the emitted frequency with the emitted power only 30 MW; the power spectrum density of the electric field was larger by an order of magnitude than the normal background, with the propagating radius exceeding 200 km. Due to the small foF2 over SURA in June at that local nighttime period,f0 in these three cases were significantly higher than foF2, all belonging to under-dense heating conditions. As for the plasma parameters, only an increase of about 100 K in ion temperature was observed on June 12; in the other two cases (with one orbit without plasma data on June 17), no obvious plasma disturbances were found. This first joint SURA-CSES experiment illustrates that the present orbit of CSES can cross quite close to the SURA facility, which can insure an effective heating time from SURA so that CSES can observe the perturbations at the topside ionosphere excited by SURA in the near region. The detection of plasma disturbances on June 12 with under-dense heating mode in local nighttime provides evidence for likely success of future related experiments between CSES and SURA, or with other HF facilities.

Retrospective analysis of GLEs and estimates of radiation risks

28 February 2017 marked 75 years since the first confident registration of solar cosmic rays (SCRs), i.e., accelerated solar particles with energies from about 106to ~1010÷ 1011eV. Modern state of the problems related to the studies of Ground Level Enhancements (GLEs) of relativistic SCRs is critically analyzed based on available direct and proxy data. We are also taking into account extremely large fluxes of non-relativistic solar energetic particles (SEPs). Both kinds of SCR events are of great astrophysical and geo-scientific (geophysical) interests. A number of the GLE properties (total statistics, occurrence rate, longitude distribution, ranking of GLEs, a number of specific GLEs – so-called “rogue” SEP events etc.) are discussed in some detail. We note also the problems of GLE identification (definition) by ground-based observations, the difficulties in the studies of weak (“hidden”, or sub-) GLEs etc. One of serious challenges to the problem of radiation hazard in space is a lack of a clear, unambiguous relation between the fluxes (fluences) of relativistic SCR and non-relativistic SEPs. Special attention is paid to the recent debate on the validity, origin and properties of the “ancient” events AD775, AD994, AD1859 (Carrington event) and BC3372. We demonstrate that, in spite of existing uncertainties in proton fluences above 30 MeV, all of them are fitted well by a unique distribution function, at least, with the present level of solar activity. Extremely large SEP events are shown to obey a probabilistic distribution on their fluences with a sharp break in the range of large fluences (or low probabilities). The studies of this kind may be extended for periods with different levels of solar activity in the past and/or in the future. Dose rates at aircraft altitudes are also demonstrated during some GLEs. Several examples of using the SCR data and GLE properties in radiation prediction schemes are considered.

Relationship between Intensity of White-light Flares and Proton Flux of Solar Energetic Particles

Solar energetic particles (SEPs), including protons and heavy ions, are believed to be accelerated either by CME shock or by magnetic reconnection. The latter also produces solar flares, in which the white light flares (WLFs) are among the most energetic ones. Magnetic reconnections occur in the corona and the accelerated particles propagate both downward and upward along the magnetic loops. The former is the source of flare emission and the latter is thought to be SEPs. Therefore, a comparison between flare emission and SEP events provides valuable constraint in determining the acceleration site of SEPs. We collect 43 SEP events, observed from 2010 to 2017, and investigate their correlation with WL emission and SXR flus, observed by SDO/HMI and GOES, respectively. Our preliminary results show: 1) Among 47 SEP events, 39 of which do not have detectable flare emissions in white light and SXR. 2) Most strong WLFs are not associated with SEPs. 3) No clear correlation is found between the proton flux and the equivalent area, a quantity that measures the magnitude of WLF emission. A straightforward speculation is that the acceleration process could be different for SEPs and the energetic electrons powering WLFs in the events analyzed.

What can the annual 10Be solar activity reconstructions tell us about historic space weather?

Context: Cosmogenic isotopes provide useful estimates of past solar magnetic activity, constraining past space climate with reasonable uncertainty. Much less is known about past space weather conditions. Recent advances in the analysis of 10Be by McCracken & Beer (2015, Sol Phys 290: 305–3069) (MB15) suggest that annually resolved 10Be can be significantly affected by solar energetic particle (SEP) fluxes. This poses a problem, and presents an opportunity, as the accurate quantification of past solar magnetic activity requires the SEP effects to be determined and isolated, whilst doing so might provide a valuable record of past SEP fluxes. Aims: We compare the MB15 reconstruction of the heliospheric magnetic field (HMF), with two independent estimates of the HMF derived from sunspot records and geomagnetic variability. We aim to quantify the differences between the HMF reconstructions, and speculate on the origin of these differences. We test whether the differences between the reconstructions appear to depend on known significant space weather events. Methods: We analyse the distributions of the differences between the HMF reconstructions. We consider how the differences vary as a function of solar cycle phase, and, using a Kolmogorov-Smirnov test, we compare the distributions under the two conditions of whether or not large space weather events were known to have occurred. Results: We find that the MB15 reconstructions are generally marginally smaller in magnitude than the sunspot and geomagnetic HMF reconstructions. This bias varies as a function of solar cycle phase, and is largest in the declining phase of the solar cycle. We find that MB15's excision of the years with very large ground level enhancement (GLE) improves the agreement of the 10Be HMF estimate with the sunspot and geomagnetic reconstructions. We find no statistical evidence that GLEs, in general, affect the MB15 reconstruction, but this analysis is limited by having too few samples. We do find evidence that the MB15 reconstructions appear statistically different in years with great geomagnetic storms.

Space Weather Service for Chinese Space Science Satellites

Strategic Priority Research Program on Space Science has gained remarkable achievements. Space Environment Prediction Center (SEPC) affiliated with the National Space Science Center (NSSC) has been providing space weather services and helps secure space missions. Presently, SEPC is capable to offer a variety of space weather services covering many phases of space science missions including planning, design, launch, and orbital operation. The service packages consist of space weather forecasts, warnings, and effect analysis that can be utilized to avoid potential space weather hazard or reduce the damage caused by space storms, space radiation exposure for example. Extensive solar storms that occurred over Chinese Ghost Festival (CGF) in September 2017 led to a large enhancement of the solar energetic particle flux at 1 AU, which affected the near Earth radiation environment and brought great threat to orbiting satellites. Based on the space weather service by SEPC, satellite ground support groups collaborating with the space Tracking, Telemetering and Command system (TT&C) team were able to take immediate measures to react to the CGF solar storm event.

The onset of energetic particle irradiation in Class 0 protostars

The early stages of low-mass star formation are likely to be subject to intense ionization by protostellar energetic MeV particles. As a result, the surrounding gas is enriched in molecular ions, such as HCO$^{+}$ and N$_{2}$H$^{+}$. Nonetheless, this phenomenon remains poorly understood for Class 0 objects. Recently, based on Herschel observations taken as part of the key program Chemical HErschel Surveys of Star forming regions (CHESS), a very low HCO$^{+}$/N$_{2}$H$^{+}$ abundance ratio of about 3-4, has been reported toward the protocluster OMC-2 FIR4. This finding suggests a cosmic-ray ionization rate in excess of 10$^{-14}$ s$^{-1}$, much higher than the canonical value of $\zeta$ = 3$\times$10$^{-17}$ s$^{-1}$ (value expected in quiescent dense clouds). To assess the specificity of OMC-2 FIR4, we have extended this study to a sample of sources in low- and intermediate mass. More specifically, we seek to measure the HCO$^{+}$/N$_2$H$^{+}$ abundance ratio from high energy lines (J $\ge$ 6) toward this source sample in order to infer the flux of energetic particles in the warm and dense gas surrounding the protostars. We use observations performed with the Heterodyne Instrument for the FarInfrared spectrometer on board the Herschel Space Observatory toward a sample of 9 protostars. We report HCO$^{+}$/N$_2$H$^{+}$ abundance ratios in the range of 5 up to 73 toward our source sample. The large error bars do not allow us to conclude whether OMC-2~FIR4 is a peculiar source. Nonetheless, an important result is that the measured HCO$^{+}$/N$_2$H$^{+}$ ratio does not vary with the source luminosity. At the present time, OMC-2 FIR4 remains the only source where a high flux of energetic particles is clearly evident. More sensitive and higher angular resolution observations are required to further investigate this process.

A Satellite Data Analysis and CubeSat Instrument Simulator Tool for Simultaneous Multi-spacecraft Measurements of Solar Energetic Particles

This paper presents a Multi-satellite Data Analysis and Simulator Tool (MDAST), developed with the original goal to support the science requirements of a Martian 3-Unit CubeSat mission profile named Bleeping Interplanetary Radiation Determination Yo-yo (BIRDY). MDAST was firstly designed and tested by taking into account the positions, attitudes, instruments field of view and energetic particles flux measurements from four spacecrafts (ACE, MSL, STEREO A, and STEREO B). Secondly, the simulated positions, attitudes and instrument field of view from the BIRDY CubeSat have been adapted for input. And finally, this tool can be used for data analysis of the measurements from the four spacecrafts mentioned above so as to simulate the instrument trajectory and observation capabilities of the BIRDY CubeSat. The onset, peak and end time of a solar particle event is specifically defined and identified with this tool. It is not only useful for the BIRDY mission but also for analyzing data from the four satellites aforementioned and can be utilized for other space weather missions with further customization.

The Energetic Particle Environment of the Lunar Nearside: SEP Influence

Abstract The energetic particle environment of the lunar nearside is quite different from that of the lunar farside. Due to the shielding of the Earth’s magnetosphere and the Moon, the lunar nearside may receive much fewer energetic particles from the Sun. It is currently impossible to directly measure the received energetic particle flux of the whole lunar surface. By using the ARTEMIS and Wind observations, we qualitatively studied the shielding effect of the Earth’s magnetosphere and the lunar body from solar energetic particles (SEPs). We found that the Earth’s magnetosphere can effectively shield SEPs with energies up to 4 Mev during the SEP event. However, in the solar wind, the Moon can provide partial shielding from SEPs with energies ≤100 KeV. SEPs with energies above 150 KeV in the lunar shadow show no difference in flux from in the solar wind, which suggests that the nearside and farside are the same in receiving SEPs with energies above 150 KeV during the SEP event.

Stochastic simulation of destruction processes in self-irradiated materials

Self-irradiation damages resulting from fission processes are common phenomena observed in nuclear fuel containing (NFC) materials. Numerous $\alpha$-decays lead to local structure transformations in NFC materials. The damages appearing due to the impacts of heavy nuclear recoils in the subsurface layer can cause detachments of material particles. Such a behaviour is similar to sputtering processes observed during a bombardment of the material surface by a flux of energetic particles. However, in the NFC material, the impacts are initiated from the bulk. In this work we propose a two-dimensional mesoscopic model to perform a stochastic simulation of the destruction processes occurring in a subsurface region of NFC material. We describe the erosion of the material surface, the evolution of its roughness and predict the detachment of the material particles. Size distributions of the emitted particles are obtained in this study. The simulation results of the model are in a qualitative agreement with the size histogram of particles produced from the material containing lava-like fuel formed during the Chernobyl nuclear power plant disaster.

Seeds of Life in Space (SOLIS)

The interstellar delivery of carbon atoms locked into molecules might be one of the key ingredients for the emergence of life. Cyanopolyynes are carbon chains delimited at their two extremities by an atom of hydrogen and a cyano group, so that they might be excellent reservoirs of carbon. The simplest member, HC3N, is ubiquitous in the galactic interstellar medium and found also in external galaxies. Thus, understanding the growth of cyanopolyynes in regions forming stars similar to our Sun, and what affects it, is particularly relevant. In the framework of the IRAM/NOEMA Large Program SOLIS (Seeds Of Life In Space), we have obtained a map of two cyanopolyynes, HC3N and HC5N, in the protocluster OMC2-FIR4. Because our Sun is thought to be born in a rich cluster, OMC2-FIR4 is one of the closest and best known representatives of the environment in which the Sun may have been born. We find a HC3N/HC5N abundance ratio across the source in the range ~ 1 - 30, with the smallest values (< 10) in FIR5 and in the Eastern region of FIR4. The ratios < 10 can be reproduced by chemical models only if: (1) the cosmic-ray ionisation rate $\zeta$ is ~ $4 \times 10^{-14}$ s$^{-1}$; (2) the gaseous elemental ratio C/O is close to unity; (3) O and C are largely depleted. The large $\zeta$ is comparable to that measured in FIR4 by previous works and was interpreted as due to a flux of energetic (> 10 MeV) particles from embedded sources. We suggest that these sources could lie East of FIR4 and FIR5. A temperature gradient across FIR4, with T decreasing by about 10 K, could also explain the observed change in the HC3N/HC5N line ratio, without the need of a cosmic ray ionisation rate gradient. However, even in this case, a high constant cosmic-ray ionisation rate (of the order of $10^{-14}$ s$^{-1}$) is necessary to reproduce the observations.

Evolution of Energetic Particle Fluxes in the Early Heliosphere

The variations in the fluxes of protons in the heliosphere owing to the reduction over time of the rate of mass loss by the sun and its flow speed are calculated over its entire lifetime. Two groups of protons are considered: those belonging to the solar wind with energies of about 1 keV corresponding to the directed flow velocity on the order of 400 km/s and those belonging to an anomalous component accelerated to energies on the order of 1-100 MeV at the boundary of the heliosphere. Approximation formulas are obtained for the variation in the differential intensities with time for both groups; these are consistent with available observational and theoretical data. They are used to obtain analytical dependences for the irradiation rate of water ice during different stages of the evolution of the heliosphere which are important for analyzing the radiation chemical transformation of ices in the solar system.

Long-term variations of polar mesospheric summer echoes observed at Andøya (69°N)

Polar mesosphere summer echoes (PMSE) are strong radar signals received at very high radar frequencies at altitudes between about 80 and 95 km at polar latitudes during summer. PMSE are caused by inhomogeneities in the electron density of the radar Bragg scale within the plasma of the cold summer mesopause region in the presence of negatively charged ice particles. Therefore, the occurrence of PMSE depends on the ionisation due to solar wave radiation and precipitating high energetic particle fluxes but also contains information about mesospheric temperature and water vapour content. Long-time observations of these echoes can be used to conclude on long-term changes of these atmospheric parameters. Continuous observations of PMSE have been carried out on the North-Norwegian island And/oya (69.3°N, 16.0°E) using the ALOMAR SOUSY radar (1994–1997), the ALWIN VHF radar (1999–2008) and the Middle Atmosphere Alomar Radar System MAARSY (since 2011). Since both the ALWIN radar and MAARSY are calibrated systems, the received echo strength of PMSE from 17 years of mesospheric observations (1999–2016) could be converted into absolute signal power. This data series could be extended to the years 1994 until 1997 on the basis of signal-to-noise ratio values derived during the years between 1994 and 2008. Seasonal mean values of PMSE occurrence for the time period from 1 June until 31 July have been derived and the resulting 23 years long data set was analyzed in dependence on solar and geomagnetic activity as well as analyzed for long-term trends. The PMSE occurrence rate is positively correlated with the solar Lyman α radiation (however low significance level) and the geomagnetic Ap index. After elimination of the solar and geomagnetically induced parts using different regression analysis methods, the PMSE data show a significant (χ = 92%–97%) positive trend during the observation period 1994 until 2016.

The 26 December 2001 Solar Eruptive Event Responsible for GLE63: III. CME, Shock Waves, and Energetic Particles

The SOL2001-12-26 moderate solar eruptive event (GOES importance M7.1, microwaves up to 4000 sfu at 9.4 GHz, CME speed 1446 km/s) produced strong fluxes of solar energetic particles and ground-level enhancement of cosmic-ray intensity (GLE63). To find a possible reason for the atypically high proton outcome of this event, we study multi-wavelength images and dynamic radio spectra and quantitatively reconcile the findings with each other. An additional eruption probably occurred in the same active region about half an hour before the main eruption. The latter produced two blast-wave-like shocks during the impulsive phase. The two shock waves eventually merged around the radial direction into a single shock traced up to $25R_\odot$ as a halo ahead of the expanding CME body, in agreement with an interplanetary Type II event recorded by the Radio and Plasma Wave Investigation (WAVES) experiment on the Wind spacecraft. The shape and kinematics of the halo indicate an intermediate regime of the shock between the blast wave and bow shock at these distances. The results show that i) the shock wave appeared during the flare rise and could accelerate particles earlier than usually assumed; ii) the particle event could be amplified by the preceding eruption, which stretched closed structures above the developing CME, facilitated its lift-off and escape of flare-accelerated particles, enabled a higher CME speed and stronger shock ahead; iii) escape of flare-accelerated particles could be additionally facilitated by reconnection of the flux rope, where they were trapped, with a large coronal hole; iv) the first eruption supplied a rich seed population accelerated by a trailing shock wave.