We study four consecutive 300–800 keV electron events observed on 1980 May 28 by Helios-1, when t... more We study four consecutive 300–800 keV electron events observed on 1980 May 28 by Helios-1, when the spacecraft was located at 0.31 au from the Sun. We use two different techniques to extract the release time history of electrons at the Sun: (1) a data-driven method based on the assumption that particles conserve their magnetic moment as they propagate between the Sun and the spacecraft and (2) an inversion method that utilizes particle transport simulation results. Both methods make use of the particle angular distributions measured relative to the local direction of the magnetic field. The general characteristics of the release time profiles obtained by these two techniques are similar, especially during their rising phases. We find indications that the strength of the interplanetary scattering varies with the size of the solar parent event, suggesting that scattering processes are not necessarily an inherent property of the medium but are related to the amount of released particles at the Sun. We use the inferred release profiles to compute the expected intensities at 1 au. In contrast to simultaneous near-Earth observations by the Interplanetary Monitoring Platform (IMP-8), our simulations predict the observation of four separate events at 1 au. Processes that could contribute to the observation of one single time-extended event at 1 au include (1) distinct magnetic connections of the spacecraft to the particle sources, (2) the spatio-temporal evolution of the particle sources, and (3) different particle transport conditions, including a variation of l r with radial distance and/or heliolongitude, as well as the possibility that electrons reached IMP-8 by diffusion perpendicular to the interplanetary magnetic field.
We analyze one of the first solar energetic particle (SEP) events of solar cycle 24 observed at w... more We analyze one of the first solar energetic particle (SEP) events of solar cycle 24 observed at widely separated spacecraft in order to assess the reliability of models currently used to determine the connectivity between the sources of SEPs at the Sun and spacecraft in the inner heliosphere. This SEP event was observed on 2010 August 14 by near-Earth spacecraft, STEREO-A (∼80° west of Earth) and STEREO-B (∼72° east of Earth). In contrast to near-Earth spacecraft, the footpoints of the nominal magnetic field lines connecting STEREO-A and STEREO-B with the Sun were separated from the region where the parent fast halo coronal mass ejection (CME) originated by ∼88° and ∼47° in longitude, respectively. We discuss the properties of the phenomena associated with this solar eruption. Extreme ultraviolet and white-light images are used to specify the extent of the associated CME-driven coronal shock. We then assess whether the SEPs observed at the three heliospheric locations were accelerated by this shock or whether transport mechanisms in the corona and/or interplanetary space provide an alternative explanation for the arrival of particles at the poorly connected spacecraft. A possible scenario consistent with the observations indicates that the observation of SEPs at STEREO-B and near Earth resulted from particle injection by the CME shock onto the field lines connecting to these spacecraft, whereas SEPs reached STEREO-A mostly via cross-field diffusive transport processes. The successes, limitations, and uncertainties of the methods used to resolve the connection between the acceleration sites of SEPs and the spacecraft are evaluated.
Interplanetary (IP) shocks provide an excellent opportunity to study energetic particle accelerat... more Interplanetary (IP) shocks provide an excellent opportunity to study energetic particle acceleration. During an IP shock related energetic storm particle (ESP) event, both the shock and the accelerated particles can be measured in-situ simultaneously. Thus, a study of in-situ IP shocks and particle distributions in their vicinity provides a meaningful way to test our theoretical understanding of shock acceleration, particularly
ABSTRACT We study the near-relativistic (NR >30 keV) electron event observed on 2000 Febru... more ABSTRACT We study the near-relativistic (NR >30 keV) electron event observed on 2000 February 18 by the Advanced Composition Explorer spacecraft. Highly collimated pitch-angle distributions were observed during the first ~2 h of the event. Roel of (2008) explained this event by assuming that the propagation of NR electrons is essentially ``scatter-free'' in the inner heliosphere and that beyond 1 AU, particles are ``back-scattered'' by magnetic field compressions and irregularities. We use Monte Carlo simulations to explore this approach. We fit observational sectored intensities to assure that the directional information contained in the data is used in full. We conclude that the event cannot be explained without assuming a back-scatter region beyond 1 AU and that NR electrons propagated under weak-scattering conditions in the inner heliosphere.
Our present knowledge of Mercury's magnetosphere is derived from two nightside Mariner 10 fl... more Our present knowledge of Mercury's magnetosphere is derived from two nightside Mariner 10 flybys in 1974 and 1975 that established the presence of an intrinsic magnetic field and of some energetic and plasma electrons. Unfortunately not even the magnetic dipole term was well-resolved, and the fluxes and identity of energetic ions have been a subject of extensive discussion and varying interpretations. MESSENGER's 14 January 2008 encounter with Mercury has provided new observations of Mercury's small and highly variable magnetosphere. Immediately prior and following the encounter, the magnetometer onboard MESSENGER indicated a northward interplanetary magnetic field (IMF). During the inbound magnetsheath passage, several-minute episodes of southward IMF were also reported, as well as substantial fluxes of both heated solar wind and planetary ions. However, observations from the Energetic Particle Spectrometer (EPS), one of two sensors for the Energetic Particle and Pla...
We have developed a Monte-Carlo technique to study the time-dependent transport of energetic part... more We have developed a Monte-Carlo technique to study the time-dependent transport of energetic particles in the interplanetary medium. We use the guiding center approximation between discrete finite pitch-angle scatterings to quantify the competing effects of focusing and pitch-angle scattering on energetic particles propagating along a Parker spiral magnetic field. The problem is formulated in terms of the parallel mean-free-path (lambda || ) and the distance traveled along a particle trajectory (s), so using the relation s=vt the results can be easily converted to time-intensity profiles and particle anisotropies observed at various distances from the Sun for electrons, protons and ions of different species. The effects from the presence of a reflecting (mirroring) magnetic boundary beyond 1 AU are discussed and compared with the effects that differential pitch-angle scattering processes produce on ions of different species and energies. The work at APL was partially supported by NA...
We examine the relation between the current sheet as derived from observations of the Sun's ... more We examine the relation between the current sheet as derived from observations of the Sun's neutral line, and recurrent particle increases associated with co-rotating interactions regions (CIR) at 4 to 5 AU radial distance as observed by the Ulysses spacecraft during its rst out-of- ecliptic orbit around the Sun. We compare observations during the ascent to high southern latitudes, close
... Decker', E Roelof', &#x... more ... Decker', E Roelof', 'vi. ... 'SJPGA [IV T 4 A LV< pue SUOYJ)GJG 1\ JOj SUIO11 ¶)O GL[4 'ApflS J 14914ThW flO HO pGSeq 'B GM 'GDUGJ] *p GM S4UBAG G JO GUO UT 1ITGSqR ST A3UBIIbGIJ uor uoioad aq nau saTGua[thaq TA GiUTh pacpadxa cqj HuT spoqs Au'2rn ...
We study four consecutive 300–800 keV electron events observed on 1980 May 28 by Helios-1, when t... more We study four consecutive 300–800 keV electron events observed on 1980 May 28 by Helios-1, when the spacecraft was located at 0.31 au from the Sun. We use two different techniques to extract the release time history of electrons at the Sun: (1) a data-driven method based on the assumption that particles conserve their magnetic moment as they propagate between the Sun and the spacecraft and (2) an inversion method that utilizes particle transport simulation results. Both methods make use of the particle angular distributions measured relative to the local direction of the magnetic field. The general characteristics of the release time profiles obtained by these two techniques are similar, especially during their rising phases. We find indications that the strength of the interplanetary scattering varies with the size of the solar parent event, suggesting that scattering processes are not necessarily an inherent property of the medium but are related to the amount of released particles at the Sun. We use the inferred release profiles to compute the expected intensities at 1 au. In contrast to simultaneous near-Earth observations by the Interplanetary Monitoring Platform (IMP-8), our simulations predict the observation of four separate events at 1 au. Processes that could contribute to the observation of one single time-extended event at 1 au include (1) distinct magnetic connections of the spacecraft to the particle sources, (2) the spatio-temporal evolution of the particle sources, and (3) different particle transport conditions, including a variation of l r with radial distance and/or heliolongitude, as well as the possibility that electrons reached IMP-8 by diffusion perpendicular to the interplanetary magnetic field.
We analyze one of the first solar energetic particle (SEP) events of solar cycle 24 observed at w... more We analyze one of the first solar energetic particle (SEP) events of solar cycle 24 observed at widely separated spacecraft in order to assess the reliability of models currently used to determine the connectivity between the sources of SEPs at the Sun and spacecraft in the inner heliosphere. This SEP event was observed on 2010 August 14 by near-Earth spacecraft, STEREO-A (∼80° west of Earth) and STEREO-B (∼72° east of Earth). In contrast to near-Earth spacecraft, the footpoints of the nominal magnetic field lines connecting STEREO-A and STEREO-B with the Sun were separated from the region where the parent fast halo coronal mass ejection (CME) originated by ∼88° and ∼47° in longitude, respectively. We discuss the properties of the phenomena associated with this solar eruption. Extreme ultraviolet and white-light images are used to specify the extent of the associated CME-driven coronal shock. We then assess whether the SEPs observed at the three heliospheric locations were accelerated by this shock or whether transport mechanisms in the corona and/or interplanetary space provide an alternative explanation for the arrival of particles at the poorly connected spacecraft. A possible scenario consistent with the observations indicates that the observation of SEPs at STEREO-B and near Earth resulted from particle injection by the CME shock onto the field lines connecting to these spacecraft, whereas SEPs reached STEREO-A mostly via cross-field diffusive transport processes. The successes, limitations, and uncertainties of the methods used to resolve the connection between the acceleration sites of SEPs and the spacecraft are evaluated.
Interplanetary (IP) shocks provide an excellent opportunity to study energetic particle accelerat... more Interplanetary (IP) shocks provide an excellent opportunity to study energetic particle acceleration. During an IP shock related energetic storm particle (ESP) event, both the shock and the accelerated particles can be measured in-situ simultaneously. Thus, a study of in-situ IP shocks and particle distributions in their vicinity provides a meaningful way to test our theoretical understanding of shock acceleration, particularly
ABSTRACT We study the near-relativistic (NR >30 keV) electron event observed on 2000 Febru... more ABSTRACT We study the near-relativistic (NR >30 keV) electron event observed on 2000 February 18 by the Advanced Composition Explorer spacecraft. Highly collimated pitch-angle distributions were observed during the first ~2 h of the event. Roel of (2008) explained this event by assuming that the propagation of NR electrons is essentially ``scatter-free'' in the inner heliosphere and that beyond 1 AU, particles are ``back-scattered'' by magnetic field compressions and irregularities. We use Monte Carlo simulations to explore this approach. We fit observational sectored intensities to assure that the directional information contained in the data is used in full. We conclude that the event cannot be explained without assuming a back-scatter region beyond 1 AU and that NR electrons propagated under weak-scattering conditions in the inner heliosphere.
Our present knowledge of Mercury's magnetosphere is derived from two nightside Mariner 10 fl... more Our present knowledge of Mercury's magnetosphere is derived from two nightside Mariner 10 flybys in 1974 and 1975 that established the presence of an intrinsic magnetic field and of some energetic and plasma electrons. Unfortunately not even the magnetic dipole term was well-resolved, and the fluxes and identity of energetic ions have been a subject of extensive discussion and varying interpretations. MESSENGER's 14 January 2008 encounter with Mercury has provided new observations of Mercury's small and highly variable magnetosphere. Immediately prior and following the encounter, the magnetometer onboard MESSENGER indicated a northward interplanetary magnetic field (IMF). During the inbound magnetsheath passage, several-minute episodes of southward IMF were also reported, as well as substantial fluxes of both heated solar wind and planetary ions. However, observations from the Energetic Particle Spectrometer (EPS), one of two sensors for the Energetic Particle and Pla...
We have developed a Monte-Carlo technique to study the time-dependent transport of energetic part... more We have developed a Monte-Carlo technique to study the time-dependent transport of energetic particles in the interplanetary medium. We use the guiding center approximation between discrete finite pitch-angle scatterings to quantify the competing effects of focusing and pitch-angle scattering on energetic particles propagating along a Parker spiral magnetic field. The problem is formulated in terms of the parallel mean-free-path (lambda || ) and the distance traveled along a particle trajectory (s), so using the relation s=vt the results can be easily converted to time-intensity profiles and particle anisotropies observed at various distances from the Sun for electrons, protons and ions of different species. The effects from the presence of a reflecting (mirroring) magnetic boundary beyond 1 AU are discussed and compared with the effects that differential pitch-angle scattering processes produce on ions of different species and energies. The work at APL was partially supported by NA...
We examine the relation between the current sheet as derived from observations of the Sun's ... more We examine the relation between the current sheet as derived from observations of the Sun's neutral line, and recurrent particle increases associated with co-rotating interactions regions (CIR) at 4 to 5 AU radial distance as observed by the Ulysses spacecraft during its rst out-of- ecliptic orbit around the Sun. We compare observations during the ascent to high southern latitudes, close
... Decker', E Roelof', &#x... more ... Decker', E Roelof', 'vi. ... 'SJPGA [IV T 4 A LV< pue SUOYJ)GJG 1\ JOj SUIO11 ¶)O GL[4 'ApflS J 14914ThW flO HO pGSeq 'B GM 'GDUGJ] *p GM S4UBAG G JO GUO UT 1ITGSqR ST A3UBIIbGIJ uor uoioad aq nau saTGua[thaq TA GiUTh pacpadxa cqj HuT spoqs Au'2rn ...
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