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1.
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
2.
Stone E.C. Cohen C.M.S. Cook W.R. Cummings A.C. Gauld B. Kecman B. Leske R.A. Mewaldt R.A. Thayer M.R. Dougherty B.L. Grumm R.L. Milliken B.D. Radocinski R.G. Wiedenbeck M.E. Christian E.R. Shuman S. von Rosenvinge T.T. 《Space Science Reviews》1998,86(1-4):357-408
The Solar Isotope Spectrometer (SIS), one of nine instruments on the Advanced Composition Explorer (ACE), is designed to provide
high- resolution measurements of the isotopic composition of energetic nuclei from He to Zn (Z=2 to 30) over the energy range
from ∼10 to ∼100 MeV nucl−1. During large solar events SIS will measure the isotopic abundances of solar energetic particles
to determine directly the composition of the solar corona and to study particle acceleration processes. During solar quiet
times SIS will measure the isotopes of low-energy cosmic rays from the Galaxy and isotopes of the anomalous cosmic-ray component,
which originates in the nearby interstellar medium. SIS has two telescopes composed of silicon solid-state detectors that
provide measurements of the nuclear charge, mass, and kinetic energy of incident nuclei. Within each telescope, particle trajectories
are measured with a pair of two-dimensional silicon-strip detectors instrumented with custom, very large-scale integrated
(VLSI) electronics to provide both position and energy-loss measurements. SIS was especially designed to achieve excellent
mass resolution under the extreme, high flux conditions encountered in large solar particle events. It provides a geometry
factor of ∼40 cm2 sr, significantly greater than earlier solar particle isotope spectrometers. A microprocessor controls the
instrument operation, sorts events into prioritized buffers on the basis of their charge, range, angle of incidence, and quality
of trajectory determination, and formats data for readout by the spacecraft. This paper describes the design and operation
of SIS and the scientific objectives that the instrument will address.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
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):335-340
Measurements below several MeV/nucleon from Wind/LEMT and ACE/ULEIS show that elements heavier than Zn (Z=30) can be enhanced by factors of ∼100 to 1000, depending on species, in 3He-rich solar energetic particle (SEP) events. Using the Solar Isotope Spectrometer (SIS) on ACE we find that even large SEP
(LSEP) shock-accelerated events at energies from ∼10 to >100 MeV/nucleon are often very iron rich and might contain admixtures
of flare seed material. Studies of ultra-heavy (UH) SEPs (with Z>30) above 10 MeV/nucleon can be used to test models of acceleration and abundance enhancements in both LSEP and 3He-rich events. We find that the long-term average composition for elements from Z=30 to 40 is similar to standard solar system values, but there is considerable event-to-event variability. Although most
of the UH fluence arrives during LSEP events, UH abundances are relatively more enhanced in 3He-rich events, with the (34<Z<40)/O ratio on average more than 50 times higher in 3He-rich events than in LSEP events. At energies >10 MeV/nucleon, the most extreme event in terms of UH composition detected
so far took place on 23 July 2004 and had a (34<Z<40)/O enhancement of ∼250–300 times the standard solar value. 相似文献
4.
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
5.
Gold R.E. Krimigis S.M. Hawkins S.E. Haggerty D.K. Lohr D.A. Fiore E. Armstrong T.P. Holland G. Lanzerotti L.J. 《Space Science Reviews》1998,86(1-4):541-562
The Electron, Proton, and Alpha Monitor (EPAM) is designed to make measurements of ions and electrons over a broad range of
energy and intensity. Through five separate solid-state detector telescopes oriented so as to provide nearly full coverage
of the unit-sphere, EPAM can uniquely distinguish ions (Ei≳50 keV) and electrons (Ee≳40 keV) providing the context for the
measurements of the high sensitivity instruments on ACE. Using a ΔE×E telescope, the instrument can determine ion elemental
abundances (E≳0.5 MeV nucl−1). The large angular coverage and high time resolution will serve to alert the other instruments
on ACE of interesting anisotropic events. The experiment is controlled by a microprocessor-based data system, and the entire
instrument has been reconfigured from the HI-SCALE instrument on the Ulysses spacecraft. Inflight calibration is achieved
using a variety of radioactive sources mounted on the reclosable telescope covers. Besides the coarse (8 channel) ion and
(4 channel) electron energy spectra, the instrument is also capable of providing energy spectra with 32 logarithmically spaced
channels using a pulse-height-analyzer. The instrument, along with its mounting bracket and radiators weighs 11.8 kg and uses
about 4.0 W of power. To demonstrate some of the capabilities of the instrument, some initial performance data are included
from a solar energetic particle event in November 1997.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
G. M. Mason A. Korth P. H. Walpole M. I. Desai T. T. Von Rosenvinge S. A. Shuman 《Space Science Reviews》2008,136(1-4):257-284
The Solar-Terrestrial Relations Observatory (STEREO) mission addresses critical problems of the physics of explosive disturbances in the solar corona, and their propagation and interactions in the interplanetary medium between the Sun and Earth. The In-Situ-Measurements of Particles and CME Transients (IMPACT) investigation observes the consequences of these disturbances and other transients at 1 AU. The generation of energetic particles is a fundamentally important feature of shock-associated Coronal Mass Ejections (CMEs) and other transients in the interplanetary medium. Multiple sensors within the IMPACT suite measure the particle population from energies just above the solar wind up to hundreds of MeV/nucleon. This paper describes a portion of the IMPACT Solar Energetic Particles (SEP) package, the Suprathermal Ion Telescope (SIT) which identifies the heavy ion composition from the suprathermal through the energetic particle range (~few 10 s of keV/nucleon to several MeV/nucleon). SIT will trace and identify processes that energize low energy ions, and characterize their transport in the interplanetary medium. SIT is a time-of-flight mass spectrometer with high sensitivity designed to derive detailed multi-species particle spectra with a cadence of 60 s, thereby enabling detailed studies of shock-accelerated and other energetic particle populations observed at 1 AU. 相似文献
7.
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
8.
We review evidence that led to the view that acceleration at shock waves driven by coronal mass ejections (CMEs) is responsible for large particle events detected at 1 AU. It appears that even if the CME bow shock acceleration is a possible model for the origin of rather low energy ions, it faces difficulties on account of the production of ions far above 1 MeV: (i) although shock waves have been demonstrated to accelerate ions to energies of some MeV nucl–1 in the interplanetary medium, their ability to achieve relativistic energies in the solar environment is unproven; (ii) SEP events producing particle enhancements at energies 100 MeV are also accompanied by flares; those accompanied only by fast CMEs have no proton signatures above 50 MeV. We emphasize detailed studies of individual high energy particle events which provide strong evidence that time-extended particle acceleration which occurs in the corona after the impulsive flare contributes to particle fluxes in space. It appears thus that the CME bow shock scenario has been overvalued and that long lasting coronal energy release processes have to be taken into account when searching for the origin of high energy SEP events. 相似文献
9.
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
10.
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
11.
Möbius E. Kistler L.M. Popecki M.A. Crocker K.N. Granoff M. Turco S. Anderson A. Demain P. Distelbrink J. Dors I. Dunphy P. Ellis S. Gaidos J. Googins J. Hayes R. Humphrey G. Kästle H. Lavasseur J. Lund E.J. Miller R. Sartori E. Shappirio M. Taylor S. Vachon P. Vosbury M. Ye V. Hovestadt D. Klecker B. Arbinger H. Künneth E. Pfeffermann E. Seidenschwang E. Gliem F. Reiche K.-U. Stöckner K. Wiewesiek W. Harasim A. Schimpfle J. Battell S. Cravens J. Murphy G. 《Space Science Reviews》1998,86(1-4):449-495
The Solar Energetic Particle Ionic Charge Analyzer (SEPICA) is the main instrument on the Advanced Composition Explorer (ACE)
to determine the ionic charge states of solar and interplanetary energetic particles in the energy range from ≈0.2 MeV nucl−1
to ≈5 MeV charge−1. The charge state of energetic ions contains key information to unravel source temperatures, acceleration,
fractionation and transport processes for these particle populations. SEPICA will have the ability to resolve individual charge
states and have a substantially larger geometric factor than its predecessor ULEZEQ on ISEE-1 and -3, on which SEPICA is based.
To achieve these two requirements at the same time, SEPICA is composed of one high-charge resolution sensor section and two
low- charge resolution, but large geometric factor sections. The charge resolution is achieved by the focusing of the incoming
ions, through a multi-slit mechanical collimator, deflection in an electrostatic analyzer with a voltage up to 30 kV, and
measurement of the impact position in the detector system. To determine the nuclear charge (element) and energy of the incoming
ions, the combination of thin-window flow-through proportional counters with isobutane as counter gas and ion-implanted solid
state detectors provide for 3 independent ΔE (energy loss) versus E (residual energy) telescopes. The multi-wire proportional
counter simultaneously determines the energy loss ΔE and the impact position of the ions. Suppression of background from penetrating
cosmic radiation is provided by an anti-coincidence system with a CsI scintillator and Si-photodiodes. The data are compressed
and formatted in a data processing unit (S3DPU) that also handles the commanding and various automatted functions of the instrument.
The S3DPU is shared with the Solar Wind Ion Charge Spectrometer (SWICS) and the Solar Wind Ion Mass Spectrometer (SWIMS) and
thus provides the same services for three of the ACE instruments. It has evolved out of a long family of data processing units
for particle spectrometers.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
12.
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
13.
Stone E.C. Cohen C.M.S. Cook W.R. Cummings A.C. Gauld B. Kecman B. Leske R.A. Mewaldt R.A. Thayer M.R. Dougherty B.L. Grumm R.L. Milliken B.D. Radocinski R.G. Wiedenbeck M.E. Christian E.R. Shuman S. Trexel H. von Rosenvinge T.T. Binns W.R. Crary D.J. Dowkontt P. Epstein J. Hink P.L. Klarmann J. Lijowski M. Olevitch M.A. 《Space Science Reviews》1998,86(1-4):285-356
The Cosmic-Ray Isotope Spectrometer is designed to cover the highest decade of the Advanced Composition Explorer's energy
interval, from ∼50 to ∼500 MeV nucl−1, with isotopic resolution for elements from Z≃2 to Z≃30. The nuclei detected in this
energy interval are predominantly cosmic rays originating in our Galaxy. This sample of galactic matter can be used to investigate
the nucleosynthesis of the parent material, as well as fractionation, acceleration, and transport processes that these particles
undergo in the Galaxy and in the interplanetary medium.
Charge and mass identification with CRIS is based on multiple measurements of dE/dx and total energy in stacks of silicon
detectors, and trajectory measurements in a scintillating optical fiber trajectory (SOFT) hodoscope. The instrument has a
geometrical factor of ∼r250 cm2 sr for isotope measurements, and should accumulate ∼5×106 stopping heavy nuclei (Z>2) in two
years of data collection under solar minimum conditions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
Gloeckler G. Cain J. Ipavich F.M. Tums E.O. Bedini P. Fisk L.A. Zurbuchen T.H. Bochsler P. Fischer J. Wimmer-Schweingruber R.F. Geiss J. Kallenbach R. 《Space Science Reviews》1998,86(1-4):497-539
The Solar Wind Ion Composition Spectrometer (SWICS) and the Solar Wind Ions Mass Spectrometer (SWIMS) on ACE are instruments
optimized for measurements of the chemical and isotopic composition of solar and interstellar matter. SWICS determines uniquely
the chemical and ionic-charge composition of the solar wind, the thermal and mean speeds of all major solar wind ions from
H through Fe at all solar wind speeds above 300 km s−1 (protons) and 170 km s−1 (Fe+16), and resolves H and He isotopes of
both solar and interstellar sources. SWICS will measure the distribution functions of both the interstellar cloud and dust
cloud pickup ions up to energies of 100 keV e−1. SWIMS will measure the chemical, isotopic and charge state composition of
the solar wind for every element between He and Ni. Each of the two instruments uses electrostatic analysis followed by a
time-of-flight and, as required, an energy measurement. The observations made with SWICS and SWIMS will make valuable contributions
to the ISTP objectives by providing information regarding the composition and energy distribution of matter entering the magnetosphere.
In addition, SWICS and SWIMS results will have an impact on many areas of solar and heliospheric physics, in particular providing
important and unique information on: (i) conditions and processes in the region of the corona where the solar wind is accelerated;
(ii) the location of the source regions of the solar wind in the corona; (iii) coronal heating processes; (iv) the extent
and causes of variations in the composition of the solar atmosphere; (v) plasma processes in the solar wind; (vi) the acceleration
of particles in the solar wind; (vii) the physics of the pickup process of interstellar He in the solar wind; and (viii) the
spatial distribution and characteristics of sources of neutral matter in the inner heliosphere.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
15.
Martin A. Lee 《Space Science Reviews》2007,130(1-4):221-229
Gradual solar energetic particle (SEP) events are evidently accelerated by coronal/interplanetary shocks driven by coronal
mass ejections. This talk addresses the different factors which determine the composition of the accelerated ions. The first
factor is the set of available seed populations including the solar wind core and suprathermal tail, remnant impulsive events
from preceding solar flares, and remnant gradual events. The second factor is the fractionation of the seed ions by the injection
process, that is, what fraction of the ions are extracted by the shock to participate in diffusive shock acceleration. Injection
is a controversial topic since it depends on the detailed electromagnetic structure of the shock transition and the transport
of ions in these structured fields, both of which are not well understood or determined theoretically. The third factor is
fractionation during the acceleration process, due to the dependence of ion transport in the turbulent electromagnetic fields
adjacent to the shock on the mass/charge ratio. Of crucial importance in the last two factors is the magnetic obliquity of
the shock. The form of the proton-excited hydromagnetic wave spectrum is also important. Finally, more subtle effects on ion
composition arise from the superposition of ion contributions over the time history of the shock along the observer’s magnetic
flux tube, and the sequence of flux tubes sampled by the observer. 相似文献
16.
B. Heber E. Keppler R.G. Marsden C. Tranquille B. Blake M. Fränz 《Space Science Reviews》2001,97(1-4):363-366
Moraal and Steenberg (1999), showed that the peak energy in the anomalous cosmic ray spectra is independent of the radial
distance up to a few AU away from the termination shock but dependent on the solar wind speed, the radius of the termination
shock and the scattering strength. In this paper we will discuss the variation of the cosmic ray oxygen energy spectrum as
measured by the Ulysses EPAC and the COSPIN/LET on board Ulysses. We found that the peak energy decreased from ∼5 MeV nucl−1, when Ulysses was at high northern heliographic latitudes embedded in the fast solar wind to ∼3.5 MeV n−1, in the streamer belt. The shift towards lower energy might also be caused by changing modulation although Voyager measurements
indicate no variation of the ACR Oxygen spectrum at ∼60 AU.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
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
18.
Solar Wind Electron Proton Alpha Monitor (SWEPAM) for the Advanced Composition Explorer 总被引:1,自引:0,他引:1
McComas D.J. Bame S.J. Barker P. Feldman W.C. Phillips J.L. Riley P. Griffee J.W. 《Space Science Reviews》1998,86(1-4):563-612
The Solar Wind Electron Proton Alpha Monitor (SWEPAM) experiment provides the bulk solar wind observations for the Advanced
Composition Explorer (ACE). These observations provide the context for elemental and isotopic composition measurements made
on ACE as well as allowing the direct examination of numerous solar wind phenomena such as coronal mass ejections, interplanetary
shocks, and solar wind fine structure, with advanced, 3-D plasma instrumentation. They also provide an ideal data set for
both heliospheric and magnetospheric multi-spacecraft studies where they can be used in conjunction with other, simultaneous
observations from spacecraft such as Ulysses. The SWEPAM observations are made simultaneously with independent electron and
ion instruments. In order to save costs for the ACE project, we recycled the flight spares from the joint NASA/ESA Ulysses
mission. Both instruments have undergone selective refurbishment as well as modernization and modifications required to meet
the ACE mission and spacecraft accommodation requirements. Both incorporate electrostatic analyzers whose fan-shaped fields
of view sweep out all pertinent look directions as the spacecraft spins. Enhancements in the SWEPAM instruments from their
original forms as Ulysses spare instruments include (1) a factor of 16 increase in the accumulation interval (and hence sensitivity)
for high energy, halo electrons; (2) halving of the effective ion-detecting CEM spacing from ∼5° on Ulysses to ∼2.5° for ACE;
and (3) the inclusion of a 20° conical swath of enhanced sensitivity coverage in order to measure suprathermal ions outside
of the solar wind beam. New control electronics and programming provide for 64-s resolution of the full electron and ion distribution
functions and cull out a subset of these observations for continuous real-time telemetry for space weather purposes.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
19.
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
20.
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