共查询到20条相似文献,搜索用时 31 毫秒
1.
M. I. Desai G. M. Mason R. E. Gold S. M. Krimigis C. M. S. Cohen R. A. Mewaldt J. E. Mazur J. R. Dwyer 《Space Science Reviews》2007,130(1-4):243-253
Using high-resolution mass spectrometers on board the Advanced Composition Explorer (ACE), we surveyed the event-averaged
∼0.1–60 MeV/nuc heavy ion elemental composition in 64 large solar energetic particle (LSEP) events of cycle 23. Our results
show the following: (1) The Fe/O ratio decreases with increasing energy up to ∼10 MeV/nuc in ∼92% of the events and up to
∼60 MeV/nuc in ∼64% of the events. (2) The rare isotope 3He is greatly enhanced over the corona or the solar wind values in 46% of the events. (3) The heavy ion abundances are not
systematically organized by the ion’s M/Q ratio when compared with the solar wind values. (4) Heavy ion abundances from C–Fe exhibit systematic M/Q-dependent enhancements that are remarkably similar to those seen in 3He-rich SEP events and CME-driven interplanetary (IP) shock events. Taken together, these results confirm the role of shocks
in energizing particles up to ∼60 MeV/nuc in the majority of large SEP events of cycle 23, but also show that the seed population
is not dominated by ions originating from the ambient corona or the thermal solar wind, as previously believed. Rather, it
appears that the source material for CME-associated large SEP events originates predominantly from a suprathermal population
with a heavy ion enrichment pattern that is organized according to the ion’s mass-per-charge ratio. These new results indicate
that current LSEP models must include the routine production of this dynamic suprathermal seed population as a critical pre-cursor
to the CME shock acceleration process. 相似文献
2.
G. M. Mason 《Space Science Reviews》2007,130(1-4):231-242
3He-rich solar energetic particle (SEP) events show huge enrichments of 3He and association with kilovolt electrons and Type-III radio bursts. Observations from a new generation of high resolution
instruments launched on the Wind, ACE, Yohkoh, SOHO, TRACE, and RHESSI spacecraft have revealed many new properties of these
events: the particle energy spectra are found to be either power-law or curved in shape, with the 3He spectrum often being distinctly different from other species. Ultra-heavy nuclei up to >200 amu are found to be routinely
present at average enrichments of >200 times solar-system abundances. The high ionization states previously observed near
∼1 MeV/nucleon have been found to decrease towards normal solar coronal values in these events. The source regions have been
identified for many events, and are associated with X-ray jets and EUV flares that are associated with magnetic reconnection
sites near active regions. This paper reviews the current experimental picture and theoretical models, with emphasis on the
new insights found in the last few years. 相似文献
3.
R. A. Mewaldt M. D. Looper C. M. S. Cohen D. K. Haggerty A. W. Labrador R. A. Leske G. M. Mason J. E. Mazur T. T. von Rosenvinge 《Space Science Reviews》2012,171(1-4):97-120
We report spacecraft measurements of the energy spectra of solar protons and other solar energetic particle properties during the 16 Ground Level Events (GLEs) of Solar Cycle 23. The measurements were made by eight instruments on the ACE, GOES, SAMPEX, and STEREO spacecraft and extend from ~0.1 to ~500–700?MeV. All of the proton spectra exhibit spectral breaks at energies ranging from ~2 to ~46?MeV and all are well fit by a double power-law shape. A comparison of GLE events with a larger sample of other solar energetic particle (SEP) events shows that the typical spectral indices are harder in GLE events, with a mean slope of ?3.18 at >40?MeV/nuc. In the energy range 45 to 80?MeV/nucleon about ~50?% of GLE events have properties in common with impulsive 3He-rich SEP events, including enrichments in Ne/O, Fe/O, 22Ne/20Ne, and elevated mean charge states of Fe. These 3He-rich events contribute to the seed population accelerated by CME-driven shocks. An analysis is presented of whether highly-ionized Fe ions observed in five events could be due to electron stripping during shock acceleration in the low corona. Making use of stripping calculations by others and a coronal density model, we can account for events with mean Fe charge states of 〈Q Fe〉≈+20 if the acceleration starts at ~1.24–1.6 solar radii, consistent with recent comparisons of CME trajectories and type-II radio bursts. In addition, we suggest that gradual stripping of remnant ions from earlier large SEP events may also contribute a highly-ionized suprathermal seed population. We also discuss how observed SEP spectral slopes relate to the energetics of particle acceleration in GLE and other large SEP events. 相似文献
4.
R. A. Leske R. A. Mewaldt C. M. S. Cohen A. C. Cummings E. C. Stone M. E. Wiedenbeck T. T. von Rosenvinge 《Space Science Reviews》2007,130(1-4):195-205
Solar energetic particles (SEPs) provide a sample of the Sun from which solar composition may be determined. Using high-resolution
measurements from the Solar Isotope Spectrometer (SIS) onboard NASA’s Advanced Composition Explorer (ACE) spacecraft, we have
studied the isotopic composition of SEPs at energies ≥20 MeV/nucleon in large SEP events. We present SEP isotope measurements
of C, O, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni made in 49 large events from late 1997 to the present. The isotopic composition
is highly variable from one SEP event to another due to variations in seed particle composition or due to mass fractionation
that occurs during the acceleration and/or transport of these particles. We show that various isotopic and elemental enhancements
are correlated with each other, discuss the empirical corrections used to account for the compositional variability, and obtain
estimated solar isotopic abundances. We compare the solar values and their uncertainties inferred from SEPs with solar wind
and other solar system abundances and find generally good agreement. 相似文献
5.
The ionic charge of solar energetic particles (SEP) as observed in interplanetary space is an important parameter for the
diagnostic of the plasma conditions at the source region and provides fundamental information about the acceleration and propagation
processes at the Sun and in interplanetary space. In this paper we review the new measurements of ionic charge states with
advanced instrumentation onboard the SAMPEX, SOHO, and ACE spacecraft that provide for the first time ionic charge measurements
over the wide energy range of ∼0.01 to 70 MeV/nuc (for Fe), and for many individual SEP events. These new measurements show
a strong energy dependence of the mean ionic charge of heavy ions, most pronounced for iron, indicating that the previous
interpretation of the mean ionic charge being solely related to the ambient plasma temperature was too simplistic. This energy
dependence, in combination with models on acceleration, charge stripping, and solar and interplanetary propagation, provides
constraints for the temperature, density, and acceleration time scales in the acceleration region. The comparison of the measurements
with model calculations shows that for impulsive events with a large increase of Q
Fe(E) at energies ≤1 MeV/nuc the acceleration occurs low in the corona, typically at altitudes ≤0.2 R
S
. 相似文献
6.
R. A. Mewaldt C. M. S. Cohen G. M. Mason D. K. Haggerty M. I. Desai 《Space Science Reviews》2007,130(1-4):323-328
Data from ACE and GOES have been used to measure Solar Energetic Particle (SEP) fluence spectra for H, He, O, and Fe, over
the period from October 1997 to December 2005. The measurements were made by four instruments on ACE and the EPS sensor on
three GOES satellites and extend in energy from ∼0.1 MeV/nuc to ∼100 MeV/nuc. Fluence spectra for each species were fit by
conventional forms and used to investigate how the intensities, composition, and spectral shapes vary from year to year. 相似文献
7.
We review recent advances in determining the elemental, charge-state, and isotopic composition of 1 to 20 MeV per nucleon ions in solar energetic particle (SEP) events and outline our current understanding of the nature of solar and interplanetary processes which may explain the observations.The composition within individual SEP events may vary both with time and energy, and will in general be different from that in other SEP events. Average values of relative abundances measured in a large number of SEP events, however, are found to be roughly energy independent in the 1 to 20 MeV per nucleon range, and show a systematic deviation from photospheric abundances which seems to be organized in terms of the first ionization potential of the ion.Direct measurements of the charge states of SEPs have revealed the surprisingly common presence of energetic He+ along with heavy ions with typically coronal ionization states. High-resolution measurements of isotopic abundance ratios in a small number of SEP events show these to be consistent with the universal composition except for the puzzling overabundance of the SEP 22Ne/20Ne relative to this isotopes ratio in the solar wind. The broad spectrum of observed elemental abundance variations, which in their extreme result in composition anomalies characteristic of 3He-rich, heavy-ion rich and carbon-poor SEP events, along with direct measurements of the ionization states of SEPs provide essential information on the physical characteristics of, and conditions in the source regions, as well as important constraints to possible models for SEP production.It is concluded that SEP acceleration is a two-step process, beginning with plasma-wave heating of the ambient plasma in the lower corona, which may include pockets of cold material, and followed by acceleration to the observed energies by either flare-generated coronal shocks or Fermi-type processes in the corona. Interplanetary propagation as well as acceleration by interplanetary propagating shock will often further modify the composition of SEP events, especially at lower energies. 相似文献
8.
S. W. Kahler 《Space Science Reviews》2007,129(4):359-390
Electrons with near-relativistic (E≳30 keV, NrR) and relativistic (E≳0.3 MeV) energies are often observed as discrete events in the inner heliosphere following solar transient activity. Several
acceleration mechanisms have been proposed for the production of those electrons. One candidate is acceleration at MHD shocks
driven by coronal mass ejections (CMEs) with speeds ≳1000 km s−1. Many NrR electron events are temporally associated only with flares while others are associated with flares as well as with
CMEs or with radio type II shock waves. Since CME onsets and associated flares are roughly simultaneous, distinguishing the
sources of electron events is a serious challenge. On a phenomenological basis two classes of solar electron events were known
several decades ago, but recent observations have presented a more complex picture. We review early and recent observational
results to deduce different electron event classes and their viable acceleration mechanisms, defined broadly as shocks versus
flares. The NrR and relativistic electrons are treated separately. Topics covered are: solar electron injection delays from
flare impulsive phases; comparisons of electron intensities and spectra with flares, CMEs and accompanying solar energetic
proton (SEP) events; multiple spacecraft observations; two-phase electron events; coronal flares; shock-associated (SA) events;
electron spectral invariance; and solar electron intensity size distributions. This evidence suggests that CME-driven shocks
are statistically the dominant acceleration mechanism of relativistic events, but most NrR electron events result from flares.
Determining the solar origin of a given NrR or relativistic electron event remains a difficult proposition, and suggestions
for future work are given. 相似文献
9.
We review some of the new results for suprathermal electrons obtained with the 3-D Plasma and Energetic Particle Instrument
on the WIND spacecraft, which provides high sensitivity electron and ion measurements from solar wind thermal plasma up to
≳MeV energies. These results include: (1) the observation of solar impulsive electron events extending down to ∼0.5 keV energy;
(2) the observation of a turnover at ∼12 keV for electrons in a gradual large solar energetic particle (LSEP) event; (3) the
detection of a quiet-time population (the ‘superhalo’) of electrons extending up to ∼100 keV energy; and (4) the probing of
the magnetic topology and source region for magnetic clouds, using electrons. These unique WIND measurements are highly complementary
to the particle composition measurements which will be made by ACE.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
10.
Understanding properties of solar energetic particle (SEP) events associated with coronal mass ejections has been identified
as a key problem in solar-terrestrial physics. Although recent CME shock acceleration models are highly promising, detailed
agreement between theoretical predictions and observations has remained elusive. Recent observations from ACE have shown substantial
enrichments in the abundances of 3He and He+ ions which are extremely rare in the thermal solar wind plasma. Consequently, these ions act as tracers of their source material,
i.e.,
3He ions are flare suprathermals and He+ ions are interstellar pickup ions. The average heavy ion composition also exhibits unsystematic differences when compared
with the solar wind values, but correlates significantly with the ambient suprathermal material abundances. Taken together
these results provide compelling evidence that CME-driven shocks draw their source material from the ubiquitous but largely
unexplored suprathermal tail rather than from the more abundant solar wind peak. However, the suprathermal energy regime has
many more contributors and exhibits much larger variability than the solar wind, and as such needs to be investigated more
thoroughly. Answers to fundamental new questions regarding the preferred injection of the suprathermal ions, the spatial and
temporal dependence of the various sources, and the causes of their variability and their effects on the SEP properties are
needed to improve agreement between the simulations and observations. 相似文献
11.
We discuss isotopic abundance measurements of heavy (6 ≤ Z ≤ 14) solar energetic particles with energies from ∼15 to 70 MeV/nucleon,
focusing on new measurements made on SAMPEX during two large solar particle events in late 1992. These measurements are corrected
for charge/mass dependent acceleration effects to obtain estimates of coronal isotopic abundances and are compared with terrestrial
and solar wind isotope abundances. An example of new results from the Advanced Composition Explorer is included.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
12.
The solar wind charge state and elemental compositions have been measured with the Solar Wind Ion Composition Spectrometers
(SWICS) on Ulysses and ACE for a combined period of about 25 years. This most extensive data set includes all varieties of
solar wind flows and extends over more than one solar cycle. With SWICS the abundances of all charge states of He, C, N, O,
Ne, Mg, Si, S, Ar and Fe can be reliably determined (when averaged over sufficiently long time periods) under any solar wind
flow conditions. Here we report on results of our detailed analysis of the elemental composition and ionization states of
the most unbiased solar wind from the polar coronal holes during solar minimum in 1994–1996, which includes new values for
the abundance S, Ca and Ar and a more accurate determination of the 20Ne abundance. We find that in the solar minimum polar coronal hole solar wind the average freezing-in temperature is ∼1.1×106 K, increasing slightly with the mass of the ion. Using an extrapolation method we derive photospheric abundances from solar
wind composition measurements. We suggest that our solar-wind-derived values should be used for the photospheric ratios of
Ne/Fe=1.26±0.28 and Ar/Fe=0.030±0.007. 相似文献
13.
We present observations of energetic (0.34–8 MeV) ions from the Ulysses spacecraft during its second ascent to southern high latitude regions of the heliosphere. We cover the period from January
1999 until mid-2000 as Ulysses moved from 5.2 AU and 18° S to 3.5 AU and 55° S. In contrast to the long-lived and well-defined ∼26-day recurrences that
were observed throughout Ulysses‘ first southern pass, energetic ion fluxes during the first portion of the Ulysses’ second polar orbit are highly irregular. Although corotating interaction regions (CIRs) are clearly present in solar wind
and magnetic field data throughout the first half of 1999, their effects on energetic ion intensities are quite different
from what they were in 1992–1993. No dominant strictly recurrent ion flux increases are observed in association with the arrival
of these CIRs. Correspondingly, there is no stable structure of large polar coronal holes during the same period. Isolated
transient solar energetic particle (SEP) events are observed at low and high latitudes. We compare energetic ion observations
from the ACE and Ulysses spacecraft during the first half of 1999 to determine the influence of these SEP events in the observed recurrent CIR structure.
Such SEP events occurred only occasionally during 1992–1993, but when they occurred, they obscured the recurrences in a manner
similar to that observed in 1999–2000. We therefore conclude that the basic differences in the behavior of energetic ion events
between the first and second southern passes are due to the short life of the corotating structure and the higher frequency
of SEP events occurring in 1999–2000.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
The three-dimensional structure of the solar maximum modulation of cosmic rays in the heliosphere can be studied for the first
time by comparing observations from Ulysses at high solar latitudes to those from in-ecliptic spacecraft, such as IMP-8. Observations through mid-2000 show that changes
in modulation remain well correlated at Earth and Ulysses up to latitudes of ∼60° south. The observed changes seem to be best correlated with changes in the inclination of the heliospheric
current sheet. The spectral index of the proton spectra at energies <100 MeV in the ecliptic and at high latitudes remain
roughly consistent with the T
+1 spectrum expected from modulation models, while the spectral index of the helium spectrum at both locations has changed smoothly
from the flat or even negative index spectra characteristic of anomalous component fluxes toward the T
+1 galactic spectrum with increasing modulation. Intensities near the equator and at high latitude remain nearly equal, and
latitudinal gradients for nucleonic cosmic rays thus remain small (<1% deg−1) at solar maximum. In the most recent data fluxes of protons and helium with energies less than ∼100 MeV nucl−1 measured by Ulysses are smaller than those measured at IMP-8, suggesting that the gradients may have switched to become negative toward the poles
even before a clear reversal of polarity for the solar magnetic dipole has been completed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
With Ulysses approaching the south solar polar latitudes during a period of high solar activity, it is for the first time possible to
study the distribution of solar energetic particles (SEPs) in solar latitude as well as in radius and longitude. From July
1997 to August 2000, Ulysses moved from near the solar equator at ∼5 AU to ∼67° S latitude at ∼3 AU. Using observations of >∼30 MeV protons from Ulysses and IMP-8 at Earth we find good correlation between large SEP increases observed at IMP and Ulysses, almost regardless of the relative locations of the spacecraft. The observations show that within a few days after injection
of SEPs, the flux in the inner heliosphere is often almost uniform, depending only weakly on the position of the observer.
No clear effect of the increasing solar latitude of Ulysses is evident. Since the typical latitudinal extent of CMEs, which most likely accelerate the SEPs, is only ∼30°, this suggests
that the enhanced cross-field propagation for cosmic rays and CIR-accelerated particles deduced from Ulysses’ high latitude studies near solar minimum is also true for SEPs near solar maximum.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
Mason G.M. Gold R.E. Krimigis S.M. Mazur J.E. Andrews G.B. Daley K.A. Dwyer J.R. Heuerman K.F. James T.L. Kennedy M.J. LeFevere T. Malcolm H. Tossman B. Walpole P.H. 《Space Science Reviews》1998,86(1-4):409-448
The Ultra Low Energy Isotope Spectrometer (ULEIS) on the ACE spacecraft is an ultra high resolution mass spectrometer designed
to measure particle composition and energy spectra of elements He-Ni with energies from ∼45 keV nucl−1 to a few MeV nucl−1.
ULEIS will investigate particles accelerated in solar energetic particle events, interplanetary shocks, and at the solar wind
termination shock. By determining energy spectra, mass composition, and their temporal variations in conjunction with other
ACE instruments, ULEIS will greatly improve our knowledge of solar abundances, as well as other reservoirs such as the local
interstellar medium. ULEIS is designed to combine the high sensitivity required to measure low particle fluxes, along with
the capability to operate in the largest solar particle or interplanetary shock events. In addition to detailed information
for individual ions, ULEIS features a wide range of count rates for different ions and energies that will allow accurate determination
of particle fluxes and anisotropies over short (∼few minutes) time scales.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
At energies above the bulk solar wind and pick-up ion cutoff, observations reveal an interplanetary suprathermal ion population extending to ~1?MeV/nucleon and even higher energies. These suprathermal ions are found under a wide variety of conditions including periods when there are no obvious nearby accelerating shocks. We review the observational properties of these ions in quiet solar wind periods near 1?AU, including transient Corotating Interaction Region (CIR) events, and other, quieter periods in between transient enhancements. The particle energy spectra are power laws close to E ?1.5 in the range above the solar wind, rolling over at energies of a few hundred keV/nucleon to a few MeV/nucleon. Although the C/O and Fe/O ratios of the tails is close to that of the solar wind, pickup ions and 3He found in the tails indicate sources distinct from the solar wind. We briefly review several mechanisms that have been proposed to explain these ions. 相似文献
18.
R. A. Mewaldt C. M. S. Cohen W. R. Cook A. C. Cummings A. J. Davis S. Geier B. Kecman J. Klemic A. W. Labrador R. A. Leske H. Miyasaka V. Nguyen R. C. Ogliore E. C. Stone R. G. Radocinski M. E. Wiedenbeck J. Hawk S. Shuman T. T. von Rosenvinge K. Wortman 《Space Science Reviews》2008,136(1-4):285-362
The Low-Energy Telescope (LET) is one of four sensors that make up the Solar Energetic Particle (SEP) instrument of the IMPACT investigation for NASA’s STEREO mission. The LET is designed to measure the elemental composition, energy spectra, angular distributions, and arrival times of H to Ni ions over the energy range from ~3 to ~30 MeV/nucleon. It will also identify the rare isotope 3He and trans-iron nuclei with 30≤Z≤83. The SEP measurements from the two STEREO spacecraft will be combined with data from ACE and other 1-AU spacecraft to provide multipoint investigations of the energetic particles that result from interplanetary shocks driven by coronal mass ejections (CMEs) and from solar flare events. The multipoint in situ observations of SEPs and solar-wind plasma will complement STEREO images of CMEs in order to investigate their role in space weather. Each LET instrument includes a sensor system made up of an array of 14 solid-state detectors composed of 54 segments that are individually analyzed by custom Pulse Height Analysis System Integrated Circuits (PHASICs). The signals from four PHASIC chips in each LET are used by a Minimal Instruction Set Computer (MISC) to provide onboard particle identification of a dozen species in ~12 energy intervals at event rates of ~1,000 events/sec. An additional control unit, called SEP Central, gathers data from the four SEP sensors, controls the SEP bias supply, and manages the interfaces to the sensors and the SEP interface to the Instrument Data Processing Unit (IDPU). This article outlines the scientific objectives that LET will address, describes the design and operation of LET and the SEP Central electronics, and discusses the data products that will result. 相似文献
19.
The Advanced Composition Explorer 总被引:2,自引:0,他引:2
Stone E.C. Frandsen A.M. Mewaldt R.A. Christian E.R. Margolies D. Ormes J.F. Snow F. 《Space Science Reviews》1998,86(1-4):1-22
The Advanced Composition Explorer was launched August 25, 1997 carrying six high-resolution spectrometers that measure the
elemental, isotopic, and ionic charge-state composition of nuclei from H to Ni (1≤Z≤28) from solar wind energies (∼1 keV nucl−1)
to galactic cosmic-ray energies (∼500 MeV nucl−1). Data from these instruments is being used to measure and compare the elemental
and isotopic composition of the solar corona, the nearby interstellar medium, and the Galaxy, and to study particle acceleration
processes that occur in a wide range of environments. ACE also carries three instruments that provide the heliospheric context
for ion composition studies by monitoring the state of the interplanetary medium. From its orbit about the Sun-Earth libration
point ∼1.5 million km sunward of Earth, ACE also provides real-time solar wind measurements to NOAA for use in forecasting
space weather. This paper provides an introduction to the ACE mission, including overviews of the scientific goals and objectives,
the instrument payload, and the spacecraft and ground systems.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
20.
C. M. S. Cohen R. A. Mewaldt R. A. Leske A. C. Cummings E. C. Stone M. E. Wiedenbeck T. T. von Rosenvinge G. M. Mason 《Space Science Reviews》2007,130(1-4):183-194
Solar abundances can be derived from the composition of the solar wind and solar energetic particles (SEPs) as well as obtained
through spectroscopic means. Past comparisons have suggested that all three samples agree well, when rigidity-related fractionation
effects on the SEPs were accounted for. It has been known that such effects vary from one event to the next and should be
addressed on an event-by-event basis. This paper examines event variability more closely, particularly in terms of energy-dependent
SEP abundances. This is now possible using detailed SEP measurements spanning several decades in energy from the Ultra Low
Energy Isotope Spectrometer (ULEIS) and the Solar Isotope Spectrometer (SIS) on the ACE spacecraft. We present examples of
the variability of the elemental composition with energy and suggest they can be understood in terms of diffusion from the
acceleration region near the interplanetary shock. By means of a spectral scaling procedure, we obtain energy-independent
abundance ratios for 14 large SEP events and compare them to reported solar wind and coronal abundances as well as to previous
surveys of SEP events. 相似文献