C. Tranquille

Properties of a large-scale interplanetary loop structure as deduced from low-energy proton anisotropy and magnetic field measurements

We present correlated particle and magnetic field measurements by the ISEE 3 spacecraft for the loop structure behind the interplanetary traveling shock event of November 12, 1978. Following the passage of the turbulent shock region, we observe strong bidirectional streaming of low-energy protons for approximately 6 hours, corresponding to a loop thickness of about 0.07 AU. This region is also characterized by a low relative variance of the magnetic field, a depressed proton intensity, and a reduction in the magnetic power spectral density. Using quasi-linear theory applied to a slab model, we derive a value of 3 AU for the mean free path during the passage of the closed loop. We infer from this observation that the proton regime associated with the loop structure is experiencing scatter-free transport and that either the length of the loop is approximately 3 AU between the sun and the earth or else the protons are being reflected at both ends of a smaller loop.

ENERGETIC PARTICLE OBSERVATIONS AND PROPAGATION IN THE THREE-DIMENSIONAL HELIOSPHERE DURING THE 2006 DECEMBER EVENTS

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.

Radial and latitudinal gradients of anomalous cosmic ray oxygen in the inner heliosphere

We use data from the Ulysses, Advanced Composition Explorer, and Solar Terrestrial Relations Observatory spacecraft to determine the radial and latitudinal gradients of anomalous cosmic ray oxygen in two energy ranges from 4.5–15.6 MeV/nuc in the inner heliosphere for the first time during an A 0. The latitudinal gradient is consistent with zero and in the range −0.3 to 0.4%/degree, suggesting that during A<0 these particles are not able to propagate into the inner heliosphere by rapid drift along the heliospheric current sheet if the tilt of the sheet is as large as 30 degrees.

On the gradients of ACR oxygen at intermediate heliocentric distances: Ulysses/SOHO results

Abstract During 1997 and up to the present time, the heliocentric position of the Ulysses spacecraft has changed only slowly in distance and latitude, being close to the equator at a distance of ∼5 AU. This period provides an excellent opportunity to observe the evolution of the Anomalous Cosmic Ray (ACR) spectrum at a location intermediate between 1 AU and the outer heliosphere. We present ACR observations in the energy range ∼3 to 30 MeV/nucleon made using the COSPIN/LET instrument on board Ulysses and the ERNE experiment on SOHO at 1 AU. Based on these observations, which cover a latitude range of ∼0° to 20° with respect to the heliographic equator, we find a radial gradient G Γ of 18.0±2.4 %/AU and a latitudinal gradient G λ of 0.6±0.1 %/deg for ACR oxygen at 10 MeV/n, with corresponding values of 25.0±3.0 %/AU and 0.9±0.1 %/deg at 5.5 MeV/n.

Cosmic Ray, Energetic Ion and Magnetic Field Characteristics of Magnetic Clouds

Abstract We present preliminary results of a survey of the relation between magnetic clouds and Forbush decreases during the period August 1978 to May 1982, using energetic ion and magnetic field observations from ISEE-3 to identify the magnetic clouds, and ground-based observations to identify the Forbush decreases. For this analysis we have selected all the events where a magnetic cloud is associated with the passage of an interplanetary shock. We observe a Forbush decrease associated with all except one of these 31 events. We find that many of the Forbush decreases have a two step structure. When the shock arrives at the earth, a slow decrease commences, with the intensity decreasing more or less monotonically whilst the post-shock turbulent region passes over the earth. When the magnetic cloud arrives at the earth, an additional, more rapid decrease is observed, with the minimum of the decrease occuring only a few hours after the arrival of the leading edge of the cloud. We also observe events where the shock and the post-shock turbulent region play only a minor role in the Forbush decrease. In these events, little or no decrease is observed either when the shock arrives at the earth, or when the post-shock turbulent region passes over the spacecraft. A large decrease is observed when the magnetic cloud arrives at the earth, the minimum being observed only a few hours after the arrival of the leading edge of the cloud. We examine in more detail one event of the the second type. In this event, the post-shock turbulent region has a high magnetic field variance, but does not affect the cosmic rays measured by the neutron monitors. A large magnetic cloud, with low magnetic field variance, containing bi-directional energetic ions, and separated from the post-shock region by a discontinuity, follows the cloud. The decrease observed coincides with the arrival at the earth of the discontinuity at the leading edge of this magnetic cloud.

Composition Measurements over the Solar Poles Close to Solar Maximum ‐ Ulysses COSPIN/LET Observations

We present energetic particle composition measurements acquired on board the Ulysses spacecraft in 2000 and 2001 during its recent south and north polar passages. In an earlier study using data only from the south polar pass (Hofer et al., 2002), we found that the high‐latitude composition data reflected the generally high level of solar activity present during that period. The observed particle populations during the south and north polar passages comprised predominantly of solar energetic particles (SEP) accelerated in association with CMEs, rather than particles related to SIR or CIRs. In this work, we compare the energetic particle composition signatures in the two helio‐hemispheres, and find that the latest data from the north polar pass show the same transient‐dominated signature as in the south.

Galactic abundances: Report of working group 3

We summarize the various methods and their limitations and strengths to derive galactic abundances from in-situ and remote-sensing measurements, both from ground-based observations and from instruments in space. Because galactic abundances evolve in time and space it is important to obtain information with a variety of different methods covering different regions from the Very Local Insterstellar Medium (VLISM) to the distant galaxy, and different times throughout the evolution of the galaxy. We discuss the study of the present-day VLISM with neutral gas, pickup ions, and Anomalous Cosmic Rays, the study of the local interstellar medium (ISM) at distances <1.5 kpc utilizing absorption line measurements in H I clouds, and the study of galactic cosmic rays, sampling contemporary (~15 Myr) sources in the local ISM within a few kiloparsec of the solar system. Solar system abundances, derived from solar abundances and meteorite studies are discussed in several other chapters of this volume. They provide samples of matter from the ISM from the time of solar system format ion, about 4.5 Gyr ago. The evolution of galactic abundances on longer time scales is discussed in the context of nuclear synthesis in the various contributing stellar objects.

Ulysses measurements of the solar cycle variation of ∼2–40 MeV/n ions in the inner heliosphere

We present measurements of energetic (∼2 to 40 MeV/n) ion spectra and abundance ratios using the COSPIN/LET instrument flown onboard Ulysses. These measurements span almost a complete solar cycle in time and cover an extensive region of the inner heliosphere (heliocentric distance from 1 to 5 AU and heliographic latitude from the ecliptic to ±80°). We are able to characterize ions associated with solar energetic particle events and those that belong to the anomalous cosmic ray (ACR) component. Abundance ratios measured in the distinct particle regimes encountered throughout the Ulysses mission are collated and compared to similar measurements made by other spacecraft. We investigate in detail the evolution of the ACR oxygen energy spectrum during solar minimum and relate our observations to models of ACR transport.

Energetic particle composition measurements at high heliographic latitudes around the solar activity maximum

From 1999 until the end of 2000 the Ulysses spacecraft was traveling back towards the southern solar polar region from about 5 AU to less than 2.5 AU. In this time period the solar activity was close to the maximum. The results of a preliminary analysis of energetic particle composition data covering the energy range 4–20 MeV/n recorded by the COSPIN/LET instrument are shown. We attempt to use the composition signatures to identify the sources of energetic particles observed at high latitudes.

Space weathering investigations enabled by NASA's virtual heliophysical observatories

Space weathering by the plasma and energetic particle radiation environment of the heliosphere contributes to the physical and chemical evolution of exposed surfaces on airless bodies such as the Moon, asteroids, comets, and icy bodies of the outer solar system. The Multi-Source Spectral Plot (MSSP) service of the NASA Virtual Energetic Particle Observatory (VEPO) enables enhanced access and comparative global heliospheric analysis of ion flux spectra from the past and present fleet of interplanetary spacecraft for modeling of space weathering effects. Commonly red colors of low-inclination Classical Kuiper Belt Objects may be the result of specific compositional origin and spectral irradiation effects in the outer heliosphere. VEPO also enables easy comparison of flux spectra to check intercalibration issues.