ABSTRACT: We report observations of solar energetic particles obtained by the HI-SCALE and COSPIN/LET instruments onboard Ulysses during the period of isolated but intense solar activity in 2006 December, in the declining phase of the solar activity cycle. We present measurements of particle intensities and also discuss observations of particle anisotropies and composition in selected energy ranges. Active Region 10930 produced a series of major solar flares with the strongest one (X9.0) recorded on December 5 after it rotated into view on the solar east limb. Located over the South Pole of the Sun, at >72°S heliographic latitude and 2.8 AU radial distance, Ulysses provided unique measurements for assessing the nature of particle propagation to high latitudes under near-minimum solar activity conditions, in a relatively undisturbed heliosphere. The observations seem to exclude the possibility that magnetic field lines originating at low latitudes reached Ulysses, suggesting either that the energetic particles observed as large solar energetic particle (SEP) events over the South Pole of the Sun in 2006 December were released when propagating coronal waves reached high-latitude field lines connected to Ulysses, or underwent perpendicular diffusion. We also discuss comparisons with energetic particle data acquired by the STEREO and Advanced Composition Explorer in the ecliptic plane near 1 AU during this period.
The Astrophysical Journal 09/2009; 704(1):469. · 6.02 Impact Factor
ABSTRACT: Broad regions on both sides of the solar wind termination shock are populated by high intensities of non-thermal ions and electrons. The pre-shock particles in the solar wind have been measured by the spacecraft Voyager 1 (refs 1-5) and Voyager 2 (refs 3, 6). The post-shock particles in the heliosheath have also been measured by Voyager 1 (refs 3-5). It was not clear, however, what effect these particles might have on the physics of the shock transition until Voyager 2 crossed the shock on 31 August-1 September 2007 (refs 7-9). Unlike Voyager 1, Voyager 2 is making plasma measurements. Data from the plasma and magnetic field instruments on Voyager 2 indicate that non-thermal ion distributions probably have key roles in mediating dynamical processes at the termination shock and in the heliosheath. Here we report that intensities of low-energy ions measured by Voyager 2 produce non-thermal partial ion pressures in the heliosheath that are comparable to (or exceed) both the thermal plasma pressures and the scalar magnetic field pressures. We conclude that these ions are the >0.028 MeV portion of the non-thermal ion distribution that determines the termination shock structure and the acceleration of which extracts a large fraction of bulk-flow kinetic energy from the incident solar wind.
Nature 08/2008; 454(7200):67-70. · 36.28 Impact Factor
ABSTRACT: Voyager 1 (V1) began measuring precursor energetic ions and electrons from the heliospheric termination shock (TS) in July 2002. During the ensuing 2.5 years, average particle intensities rose as V1 penetrated deeper into the energetic particle foreshock of the TS. Throughout 2004, V1 observed even larger, fluctuating intensities of ions from 40 kiloelectron volts (keV) to >/=50 megaelectron volts per nucleon and of electrons from >26 keV to >/=350 keV. On day 350 of 2004 (2004/350), V1 observed an intensity spike of ions and electrons that was followed by a sustained factor of 10 increase at the lowest energies and lesser increases at higher energies, larger than any intensities since V1 was at 15 astronomical units in 1982. The estimated solar wind radial flow speed was positive (outward) at approximately +100 kilometers per second (km s(-1)) from 2004/352 until 2005/018, when the radial flows became predominantly negative (sunward) and fluctuated between approximately -50 and 0 km s(-1) until about 2005/110; they then became more positive, with recent values (2005/179) of approximately +50 km s(-1). The energetic proton spectrum averaged over the postshock period is apparently dominated by strongly heated interstellar pickup ions. We interpret these observations as evidence that V1 was crossed by the TS on 2004/351 (during a tracking gap) at 94.0 astronomical units, evidently as the shock was moving radially inward in response to decreasing solar wind ram pressure, and that V1 has remained in the heliosheath until at least mid-2005.
Science 09/2005; 309(5743):2020-4. · 31.20 Impact Factor
ABSTRACT: The Magnetospheric Imaging Instrument (MIMI) onboard the Cassini spacecraft observed the saturnian magnetosphere from January 2004 until Saturn orbit insertion (SOI) on 1 July 2004. The MIMI sensors observed frequent energetic particle activity in interplanetary space for several months before SOI. When the imaging sensor was switched to its energetic neutral atom (ENA) operating mode on 20 February 2004, at approximately 10(3) times Saturn's radius RS (0.43 astronomical units), a weak but persistent signal was observed from the magnetosphere. About 10 days before SOI, the magnetosphere exhibited a day-night asymmetry that varied with an approximately 11-hour periodicity. Once Cassini entered the magnetosphere, in situ measurements showed high concentrations of H+, H2+, O+, OH+, and H2O+ and low concentrations of N+. The radial dependence of ion intensity profiles implies neutral gas densities sufficient to produce high loss rates of trapped ions from the middle and inner magnetosphere. ENA imaging has revealed a radiation belt that resides inward of the D ring and is probably the result of double charge exchange between the main radiation belt and the upper layers of Saturn's exosphere.
Science 03/2005; 307(5713):1270-3. · 31.20 Impact Factor
ABSTRACT: The magnetospheric imaging instrument (MIMI) is a neutral and charged particle detection system on the Cassini orbiter spacecraft designed to perform both global imaging and in-situ measurements to study the overall configuration and dynamics of Saturn’s magnetosphere and its interactions with the solar wind, Saturn’s atmosphere, Titan, and the icy satellites. The processes responsible for Saturn’s aurora will be investigated; a search will be performed for substorms at Saturn; and the origins of magnetospheric hot plasmas will be determined. Further, the Jovian magnetosphere and Io torus will be imaged during Jupiter flyby. The investigative approach is twofold. (1) Perform remote sensing of the magnetospheric energetic (E > 7 keV) ion plasmas by detecting and imaging charge-exchange neutrals, created when magnetospheric ions capture electrons from ambient neutral gas. Such escaping neutrals were detected by the Voyager l spacecraft outside Saturn’s magnetosphere and can be used like photons to form images of the emitting regions, as has been demonstrated at Earth. (2) Determine through in-situ measurements the 3-D particle distribution functions including ion composition and charge states (E > 3 keV/e). The combination of in-situ measurements with global images, together with analysis and interpretation techniques that include direct “forward modeling’’ and deconvolution by tomography, is expected to yield a global assessment of magnetospheric structure and dynamics, including (a) magnetospheric ring currents and hot plasma populations, (b) magnetic field distortions, (c) electric field configuration, (d) particle injection boundaries associated with magnetic storms and substorms, and (e) the connection of the magnetosphere to ionospheric altitudes. Titan and its torus will stand out in energetic neutral images throughout the Cassini orbit, and thus serve as a continuous remote probe of ion flux variations near 20R
S (e.g., magnetopause crossings and substorm plasma injections). The Titan exosphere and its cometary interaction with magnetospheric plasmas will be imaged in detail on each flyby. The three principal sensors of MIMI consists of an ion and neutral camera (INCA), a charge–energy–mass-spectrometer (CHEMS) essentially identical to our instrument flown on the ISTP/Geotail spacecraft, and the low energy magnetospheric measurements system (LEMMS), an advanced design of one of our sensors flown on the Galileo spacecraft. The INCA head is a large geometry factor (G ∼ 2.4 cm2 sr) foil time-of-flight (TOF) camera that separately registers the incident direction of either energetic neutral atoms (ENA) or ion species (≥5∘ full width half maximum) over the range 7 keV/nuc E < 3="" mev/nuc.="" chems="" uses="" electrostatic="" deflection,="" tof,="" and="" energy="" measurement="" to="" determine="" ion="" energy,="" charge="" state,="" mass,="" and="" 3-d="" anisotropy="" in="" the="" range="" 3="" ≤="">E ≤ 220 keV/e with good (∼0.05 cm2 sr) sensitivity. LEMMS is a two-ended telescope that measures ions in the range 0.03 ≤ E ≤ 18 MeV and electrons 0.015 ≤ E≤ 0.884 MeV in the forward direction (G ∼ 0.02 cm2 sr), while high energy electrons (0.1–5 MeV) and ions (1.6–160 MeV) are measured from the back direction (G ∼ 0.4 cm2 sr). The latter are relevant to inner magnetosphere studies of diffusion processes and satellite microsignatures as well as cosmic ray albedo neutron decay (CRAND). Our analyses of Voyager energetic neutral particle and Lyman-α measurements show that INCA will provide statistically significant global magnetospheric images from a distance of ∼60 R
S every 2–3 h (every ∼10 min from ∼20 R
S). Moreover, during Titan flybys, INCA will provide images of the interaction of the Titan exosphere with the Saturn magnetosphere every 1.5 min. Time resolution for charged particle measurements can be < 0.1="" s,="" which="" is="" more="" than="" adequate="" for="" microsignature="" studies.="" data="" obtained="" during="" venus-2="" flyby="" and="" earth="" swingby="" in="" june="" and="" august="" 1999,="" respectively,="" and="" jupiter="" flyby="" in="" december="" 2000="" to="" january="" 2001="" show="" that="" the="" instrument="" is="" performing="" well,="" has="" made="" important="" and="" heretofore="" unobtainable="" measurements="" in="" interplanetary="" space="" at="" jupiter,="" and="" will="" likely="" obtain="" high-quality="" data="" throughout="" each="" orbit="" of="" the="" cassini="" mission="" at="" saturn.="" sample="" data="" from="" each="" of="" the="" three="" sensors="" during="" the="" august="" 18="" earth="" swingby="" are="" shown,="" including="" the="" first="" ena="" image="" of="" part="" of="" the="" ring="" current="" obtained="" by="" an="" instrument="" specifically="" designed="" for="" this="" purpose.="" similarily,="" measurements="" in="" cis-jovian="" space="" include="" the="" first="" detailed="" charge="" state="" determination="" of="" iogenic="" ions="" and="" several="" ena="" images="" of="" that="" planet’s="">
Space Science Reviews 08/2004; 114(1):233-329. · 3.61 Impact Factor
ABSTRACT: The outer limit of the Solar System is often considered to be at the distance from the Sun where the solar wind changes from supersonic to subsonic flow. Theory predicts that a termination shock marks this boundary, with locations ranging from a few to over 100 au (1 Au approximately 1.5 x 10(8) km, the distance from Earth to the Sun). 'Pick-up ions' that originate as interstellar neutral atoms should be accelerated to tens of MeV at the termination shock, generating anomalous cosmic rays. Here we report a large increase in the intensity of energetic particles in the outer heliosphere, as measured by an instrument on the Voyager 1 spacecraft. We argue that the spacecraft exited the supersonic solar wind and passed into the subsonic region (possibly beyond the termination shock) on about 1 August 2002 at a distance of approximately 85 Au (heliolatitude approximately 34 degrees N), then re-entered the supersonic solar wind about 200 days later at approximately 87 au from the Sun. We show that the composition of the ions accelerated at the putative termination shock is that of anomalous cosmic rays and of interstellar pick-up ions.
Nature 12/2003; 426(6962):45-8. · 36.28 Impact Factor
ABSTRACT: Recent Ulysses observations from the Sun's equator to the poles reveal fundamental properties of the three-dimensional heliosphere at the maximum in solar activity. The heliospheric magnetic field originates from a magnetic dipole oriented nearly perpendicular to, instead of nearly parallel to, the Sun's rotation axis. Magnetic fields, solar wind, and energetic charged particles from low-latitude sources reach all latitudes, including the polar caps. The very fast high-latitude wind and polar coronal holes disappear and reappear together. Solar wind speed continues to be inversely correlated with coronal temperature. The cosmic ray flux is reduced symmetrically at all latitudes.
Science 12/2003; 302(5648):1165-9. · 31.20 Impact Factor
ABSTRACT: The fluxes of O and Fe ions at high heliolatitudes measured by the HiScale instrument on Ulysses reflect the dynamical processes that affect the charged particle populations in the heliosphere. Both the O and Fe ions show The fluxes of O and Fe ions at high heliolatitudes measured by the HiScale instrument on Ulysses reflect the dynamical processes that affect the charged particle populations in the heliosphere. Both the O and Fe ions show
more latitude dependence in the first (solar minimum) orbit to high southern heliolatitudes than during the second (solar more latitude dependence in the first (solar minimum) orbit to high southern heliolatitudes than during the second (solar
maximum) orbit. The ion fluxes are larger during the solar minimum orbit; the flux levels are influenced by the occurrence maximum) orbit. The ion fluxes are larger during the solar minimum orbit; the flux levels are influenced by the occurrence
of corotating interaction regions. The Fe/O abundance ratios are found to be similar at 1 AU and at high heliolatitudes. of corotating interaction regions. The Fe/O abundance ratios are found to be similar at 1 AU and at high heliolatitudes.
Space Science Reviews 04/2001; 97(1):281-284. · 3.61 Impact Factor
ABSTRACT: In January 2000, the Ulysses spacecraft observed an ICME event at 43° S heliographic latitude and ∼ 4.1 AU. We use electron (E
e>38 keV) observations to trace the topology of the IMF embedded within the ICME. The still controversial issue of whether
ICMEs have been detached from the solar corona or are still magnetically anchored to it when they arrive at the spacecraft
is tackled. An in ecliptic ICME event is also presented.
Space Science Reviews 04/2001; 97(1):263-268. · 3.61 Impact Factor
ABSTRACT: The MIMI investigation comprises three sensors, the Ion and Neutral
Camera (INCA), Charge-Energy-Mass-Spectrometer (CHEMS), and Low Energy
Magnetospheric Measurement System (LEMMS) covering the energy ranges 7
keV/nuc <E<3 Mev/nuc (ions/ < 400 keV/nuc neutrals),
3<E<230 keV/e (ions), and 0.02 <E<18 Mev (ions)/0.015
<E<1 Mev (electrons), respectively. Also, LEMMS measures
high-energy electrons (E>3 Mev) and protons (1.6 < E < 160 Mev)
from the back end of the dual field-of-view telescope. MIMI obtained
data intermittently from October 2000 to March 2001 corresponding to
distances of ~ 103RJ upstream to ~ 103RJ downstream of the planet. The
first unambiguous image of Energetic Neutral Atoms (ENA) was seen at ~
1155RJ upstream and occupied one pixel in INCA at ~ 3% statistics. The
observed intensity in the range ~ 15 to 55 keV (hydrogen) corresponds to
~ 0.08 (cm2 s keV)-1 when scaled to 100 RJ., i.e. similar to
expectations based on Voyager 1 observations some 21 years earlier. Many
images were obtained through, and past, closest approach (140 RJ;
Mitchell et al, this AGU). In addition to ENA's, the CHEMS sensor
detected several ion species of Jovian (O+, S+, SO2+, etc) and
interstellar (He+) origin in the upstream medium that manifested
themselves as pick-up and accelerated components, suggesting that
cis-Jovian space is dominated by a nebula populated by volcanic gases
from Io (Hamilton, et al, this AGU). Energetic electrons and ion events
(LEMMS) were also present upstream and marked each crossing of the
extended bow shock and magnetopause of the planet. While in the
magnetosphere, field-aligned electron distributions provided unambiguous
evidence of closed field lines to at least 200 RJ downstream from
Jupiter. Simultaneously, highly charged (S3+, S4+, O3+, O2+, etc) ions
were seen, suggesting that plasma outflow in the dusk magnetotail is
dominated by magnetospheric rather than solar wind plasma. Evidence that
Jovian plasmas are present to at least ~ 850RJ downstream will be
presented and implications discussed on overall outflow of
AGU Spring Meeting Abstracts. 04/2001; -1.
ABSTRACT: Charged particle instrumentation that will be flying on six spacecraft in the heliosphere between 1 and 90 AU during 2001–2004
will provide a global view of the interplanetary medium that has not heretofore been available. Comparative analyses of the
data that will be obtained will provide new understanding of the global evolution of heliospheric features such as traveling
shock waves, coronal mass ejections, solar activity-produced particle injections, and anomalous cosmic rays.
Space Science Reviews 01/2001; 97(1):243-248. · 3.61 Impact Factor
ABSTRACT: Prior studies have identified particle propagation channels in the
interplanetary medium where nearly scatter-free propagation occurs.
These channels have been identified to exist as far away from the Sun as
~ 4 AU. We report here a study that has examined, using spacecraft-based
instrumentation, the nature of the fluctuations of the interplanetary
magnetic fields inside two such propagation channels as well as in the
regions outside the channels. We show that the power spectral
fluctuations of the total magnitude of the magnetic field in the entire
channel duration encountered are the order of a factor of 10 lower
inside the channels than outside. Somewhat surprisingly, in the 1-40 mHz
frequency range, we find little change in the slope of the power law
spectra from outside to inside the channels. These results provide
evidence that the dominant control on the particle pitch angle diffusion
coefficients in the channels is the level of power available for
particle scattering, and not changes in the shape of the spectra
themselves. We have examined the power spectra of each component of the
magnetic field and determined that the loss of spectral power is due to
a reduction of compressible fluctuations, the solenoidal components of
the spectra remaining similar inside and outside the channels.
Astronomy and Astrophysics 10/1999; 351:385-392. · 4.59 Impact Factor
ABSTRACT: 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.
Space Science Reviews 06/1998; 86(1):541-562. · 3.61 Impact Factor
ABSTRACT: Low energy ion and electron measurements made over the south and north
polar regions of the sun by the HI-SCALE instrument on the Ulysses
spacecraft during its solar minimum polar passages are summarized. The
polar flux levels were considerably reduced in comparison to fluxes in
the vicinity of the heliospheric current sheet. Flux variations with a
period of ~26days were seen to nearly 80degS but were not observed over
the northern pole. Solar particle events originating from
near-equatorial activity were seen at high southern latitudes, but not
at high northern latitudes. Comparisons with in-ecliptic measurements
made during the same time interval on the IMP8 spacecraft suggest that
the polar differences are largely spatial and not temporal. The flux of
low energy (~0.8-5.0MeV/nucl) anomalous oxygen was measured to be ~50%
higher over the northern polar region than in the south. The flux of
solar wind iron, measurable because of its convection into the
instrument by the high speed polar solar wind, is estimated to be about
a factor of two larger over the south pole than over the north.
Astronomy and Astrophysics 11/1996; 316:457-463. · 4.59 Impact Factor
ABSTRACT: In this paper we analyze a solar particle event that was measured at two
locations in the heliosphere. Ulysses was at 40°north heliolatitude
and 130°west in heliolongitude from Earth while WIND was near Earth
at 1 AU in the ecliptic plane. To establish the origin of the particle
events, solar coronal activity is investigated. Direct observational
evidence of the association between long-duration electron acceleration
and a solar radio noise storm is shown. We also establish that the
interplanetary type III burst studied here is produced by successive
electron injections from distinct coronal locations. Two particle
increases are observed during the event. For the first one, the
particles are shown to be from coronal origin; for the second one, which
is associated with a Forbush decrease, the particles are primarily shock
accelerated. The differences in particle intensities observed at WIND
and Ulysses are explained by the nature of the particle propagation to
the spacecraft locations.
Astronomy and Astrophysics 11/1996; 316:499-505. · 4.59 Impact Factor
ABSTRACT: Low-energy (≳50 keV) charged particles measured by the HI-SCALE instrument on the Ulysses spacecraft provided unique information
on the particle composition and intensity in both polar regions of the Sun. Further, the rapid 160° South-to-North solar transit
of Ulysses in early 1995 yielded new information on heliospheric structure. This paper reviews several of the key HI-SCALE
results, including the latitude dependence of particle acceleration by corotating interaction regions, particle propagation
from equatorial regions of the Sun to high heliolatitudes, and the appearance of numerous periodic components in the power
spectra of the particle variations, the frequencies of which are consistent with those estimated (but not as yet confirmed)
for gravity-mode oscillations of the Sun.
Nuovo Cimento- Societa Italiana di Fisica Sezione C 10/1996; 19(6):927-933. · 0.35 Impact Factor
ABSTRACT: Intense, magnetic field-aligned, bidirectional, energetic (>15 kiloelectron volts) electron beams were discovered by the Galileo energetic particles detector during the flyby of Io. These beams can carry sufficient energy flux into Jupiter's atmosphere to produce a visible aurora at the footprint of the magnetic flux tube connecting Io to Jupiter. Composition measurements through the torus showed that the spatial distributions of protons, oxygen, and sulfur are different, with sulfur being the dominant energetic (> approximately 10 kiloelectron volts per nucleon) ion at closest approach.
Science 10/1996; 274(5286):401-3. · 31.20 Impact Factor
ABSTRACT: The heliosphere instrument for spectrum, composition, and anisotropy (HISCALE) recorded the fluxes of low-energy ions and electrons (> 50 kiloelectron volts) when Ulysses crossed the southern solar polar region and revealed that the large-scale structure of the heliosphere to at least approximately -75 degrees was significantly influenced by the near-equatorial heliospheric current sheet. Electrons in particular were accelerated by the current sheet-produced and poleward-propagating interplanetary reverse shock at helioradii far from the Ulysses location. At heliolatitudes higher than approximately -75 degrees on the Ulysses ascent to the pole and approximately -50 degrees on the descent, small, less regular enhancements of the lowest energy electron fluxes were measured whose relations to the current sheet were less clear. The anomalous component of low-energy (approximately 2 to 5 megaelectron volts per nucleon) oxygen flux at the highest heliolatitudes was found to be approximately 10(-8) [per square centimeter per second per steradian (per kiloelectronvolt per nucleon)]; the anomalous Ne/O ratio was approximately 0.25.
Science 06/1995; 268(5213):1010-3. · 31.20 Impact Factor
ABSTRACT: Throughout 1993, as the Ulysses spacecraft traveled from 23 to 45 south heliolatitude, the HI-SCALE instrument on the spacecraft measured a recurrent series of enhanced particle fluxes with a recurrence period of 26.5 days. These particles are accelerated from a background seed population by the corotating interaction regions (CIRs) associated with a southern solar polar coronal hole. Using the Wart detector telescope of the HI-SCALE instrument, we have analyzed the elemental abundances of C, N, O, and Fe relative to He for 0.5–4.0 MeV/nucl ions and Ne, Mg, and Si for 1.0–4.0 MeV/nucl ions in the CIRs. We compare the relative abundances to some previous measurements reported from 1 A.U. as well as with solar photosphere abundances. We note that HI-SCALE measurements of the heliolatitude dependence of the oxygen abundance and spectrum as reported by Lanzerottiet al. (1994) suggest that a substantial fraction of the seed population for the CIR-accelerated oxygen is likely to be the anomalous oxygen component of the cosmic rays.
Space Science Reviews 03/1995; 72(1):297-302. · 3.61 Impact Factor