Showing papers on "Heliosphere published in 1995"

MHD structures, waves and turbulence in the solar wind : observations and theories

Abstract: A comprehensive overview is presented of recent observational and theoretical results on solar wind structures and fluctuations and magnetohydrodynamic waves and turbulence, with preference given to phenomena in the inner heliosphere. Emphasis is placed on the progress made in the past decade in the understanding of the nature and origin of especially small-scale, compressible and incompressible fluctuations. Turbulence models to describe the spatial transport and spectral transfer of the fluctuations in the inner heliosphere are discussed, and results from direct numerical simulations are dealt with. Intermittency of solar wind fluctuations and their statistical distributions are briefly investigated. Studies of the heating and acceleration effects of the turbulence on the background wind are critically surveyed. Finally, open questions concerning the origin, nature and evolution of the fluctuations are listed, and possible avenues and perspectives for future research are outlined.

MHD Structures, Waves and Turbulence in the Solar Wind: Observations and Theories

Abstract: A comprehensive overview is presented of recent observational and theoretical results on solar wind structures and fluctuations and magnetohydrodynamic waves and turbulence, with preference given to phenomena in the inner heliosphere. Emphasis is placed on the progress made in the past decade in the understanding of the nature and origin of especially small-scale, compressible and incompressible fluctuations. Turbulence models to describe the spatial transport and spectral transfer of the fluctuations in the inner heliosphere are discussed, and results from direct numerical simulations are dealt with. Intermittency of solar wind fluctuations and their statistical distributions are briefly investigated. Studies of the heating and acceleration effects of the turbulence on the background wind are critically surveyed. Finally, open questions concerning the origin, nature and evolution of the fluctuations are listed, and possible avenues and perspectives for future research are outlined.

Ulysses solar wind plasma observations from pole to pole

Abstract: We present Ulysses solar wind plasma data from the peak southerly latitude of −80.2° on 12 September 1994 through the corresponding northerly latitude on 31 July 1995. Ulysses encountered fast wind throughout this time except for a 43° band centered on the solar equator. Median mass flux was nearly constant with latitude, while speed and density had positive and negative poleward gradients, respectively. Solar wind momentum flux was highest at high latitudes, suggesting a latitudinal asymmetry in the heliopause cross section. Solar wind energy flux density was also highest at high latitudes.

The heliospheric magnetic field over the South polar region of the sun.

Abstract: Magnetic field measurements from the Ulysses space mission overthe south polar regions of the sun showed that the structure and properties of the three-dimensional heliosphere were determined by the fast solar wind flow and magnetic fields from the large coronal holes in the polar regions of the sun. This conclusion applies at the current, minimum phase of the 11-year solar activity cycle. Unexpectedly, the radial component of the magnetic field was independent of latitude. The high-latitude magnetic field deviated significantly from the expected Parker geometry, probably because of large amplitude transverse fluctuations. Low-frequency fluctuations had a high level of variance. The rate of occurrence of discontinuities also increased significantly at high latitudes.

Three‐dimensional magnetic reconnection and the magnetic topology of coronal mass ejection events

Abstract: Measurements of superthermal electron fluxes in the solar wind indicate that field lines within coronal mass ejections, CMEs, near and beyond 1 AU are normally connected to the Sun at both ends. However, on occasion some field lines embedded deep within CMEs appear to be connected to the Sun at only one end. Here we propose an explanation for how such field lines arise in terms of 3-dimensional reconnection close to the Sun. Such reconnection also provides a natural explanation for the flux rope topology characteristic of many CMEs as well as the coronal loops formed during long-duration, solar X-ray events. Our consideration of the field topologies resulting from 3-dimensional reconnection indicates that field lines within and near CMEs may on occasion be connected to the outer heliosphere at both ends.

Interaction of the solar wind with the local interstellar medium

Abstract: First results from a two-dimensional (axisymmetric) time-dependent gas dynamic model for the interaction of the solar wind with the local interstellar medium are presented The model includes the mutual influence of the interstellar and interplanetary plasma (protons and electrons) and the neutral interstellar hydrogen atoms Neutrals created by charge exchange with the solar wind are ignored; this allows us to approximate the dynamical evolution of the system with the isotropic fluid equations A supersonic interstellar wind is assumed The global structure of the heliosphere and interaction region is described for both the plasma and neutral gas The self-consistent model is compared to a noninteracting gas dynamic model, and dramatic differences in the size of the heliosphere are found The distribution of neutral hydrogen in the heliosphere is also discussed

Characteristics of nearby interstellar matter

Abstract: There is a warm tenuous partially ionized cloud (T∼104 K,n(HI)∼0.1 cm−3,n(Hii∼ 0.22–0.44 cm−3) surrounding the solar system which regulates the environment of the solar system, determines the structure of the heliopause region, and feeds neutral interstellar gas into the inner solar system. The velocity (V∼−20 km s−1 froml∼335°,b∼0° in the local standard of rest) and enhanced Caii and Feii abundances of this cloud suggest an origin as evaporated gas from cloud surfaces in the Scorpius-Centaurus Association. Although the soft X-ray emission attributed to the ‘Local Bubble’ is enigmatic, optical and ultraviolet data are consistent with bubble formation caused by star formation epochs in the Scorpius-Centaurus Association as regulated by the nearby spiral arm configuration. The cloud surrounding the solar system (the ‘local fluff’) appears to be the leading region of an expanding interstellar structure (the ‘squall line’) which contains a magnetic field causing polarization of the light of nearby stars, and also absorption features in nearby upwind stars. The velocity vectors of the solar system and local fluff are perpendicular in the local standard of rest. Combining this information with the low column densities seen towards Sirius in the anti-apex direction, and the assumption that the cloud velocity vector is parallel to the surface normal, suggests that the Sun entered the local fluff within the historical past (less than 10 000 years ago) and is skimming the surface of the cloud. Comparison of magnesium absorption lines towards Sirius and anomalous cosmic-ray data suggest the local fluff is in ionization equilibrium.

Ulysses solar wind plasma observations at high southerly latitudes.

Abstract: Solar wind plasma observations made by the Ulysses spacecraft through –80.2° solar latitude and continuing equatorward to –40.1° are summarized. Recurrent high-speed streams and corotating interaction regions dominated at middle latitudes. The speed of the solar wind was typically 700 to 800 kilometers per second poleward of –35°. Corotating reverse shocks persisted farther south than did forward shocks because of the tilt of the heliomagnetic streamer belt. Sporadic coronal mass ejections were seen as far south as –60.5°. Proton temperature was higher and the electron strahl was broader at higher latitudes. The high-latitude wind contained compressional, pressure-balanced, and Alfvenic structures.

Shock-wave propagation in the nonuniform interstellar medium

Abstract: The development of different analytical and approximate numerical methods for calculations of shock-wave propagation in the inhomogeneous interstellar medium is reviewed. The models of ultracompact H II regions, nonspherical supernova remnants, bubbles produced by stellar winds of hot stars, and expanding supershells are discussed on the basis of these calculations.

Radial evolution of the solar wind from IMP 8 to Voyager 2

Abstract: Voyager 2 and Interplanetary Monitoring Platform (IMP) 8 data from 1977 through 1994 are presented and compared. Radial velocity and temperature structures remain intact over the distance from 1 to 43 AU, but density structures do not. Temperature and velocity changes are correlated and nearly in phase at 1 AU, but in the outer heliosphere temperature changes lead velocity changes by tens of days. Solar cycle variations are detected by both spacecraft, with minima in flux density and dynamic pressure near solar maxima. Differences between Voyager 2 and IMP 8 observations near the solar minimum in 1986-1987 are attributed to latitudinal gradients in solar wind properties. Solar rotation variations are often present even at 40 AU. The Voyager 2 temperature profile is best fit with a R(exp -0.49 +/- 0.01) decrease, much less steep than an adiabatic profile.

Ulysses observations of the radial magnetic field

Abstract: The radial component of the magnetic field in the southern hemisphere has been measured at Ulysses as it traveled from the equator to −80.2° latitude and returned. The radial component multiplied by the square of the radial distance, i.e., BRr², averaged over 77 day intervals (three solar rotations) is approximately constant at −3.5 nT and shows no evidence of a dependence on heliographic latitude. To discriminate against possible time variations, the measurements have been compared with simultaneous observations in the ecliptic by IMP-8. The two sets of observations agree very well confirming the absence of a significant latitude gradient. Since the sun's dipolar magnetic field component is strong at this phase of the sunspot cycle, it is inferred that magnetic flux from the polar cap is transported to lower latitudes in the solar wind source region to produce a uniform radial field. Such a configuration would be expected if magnetic stresses are influencing the solar wind flow near the sun and are contributing to a non-radial deflection. Estimates of the flux of open field lines (3 × 1014 webers), of the non-radial solar wind expansion (∼3) and the polar cap magnetic field strength (∼5 Gauss) are derived.

Ulysses observations of Alfvén waves in the southern and northern solar hemispheres

Abstract: Alfven waves with periods from 10 hours are shown to be continuously present in the sun's south and north polar regions. Below ≃30° latitude, as revealed by the rapid traversal of the equatorial region by Ulysses, the wave power averaged over a solar rotation decreases abruptly. The correlations between magnetic field and solar wind velocity fluctuations, upon which the wave identification is based, indicate outward propagation in both hemispheres. The Ulysses observations are consistent with many of the properties of Alfven waves seen in the ecliptic in association with high speed streams. Some implications of the waves in the polar regions are explored. Because of the long wavelengths, which reach ≃0.3 AU, the waves resonate with 10-10 3 MeV/nucleon galactic cosmic rays and oppose their entry into the polar caps. The wave amplitudes imply a contribution to the acceleration of the high latitude wind due to momentum transfer of only a few percent.

SWAN: A Study of Solar Wind Anisotropies on SOHO With Lyman Alpha Sky Mapping

Abstract: On board the SOHO spacecraft poised at L1 Lagrange point, the SWAN instrument is mainly devoted to the measurement of large scale structures of the solar wind, and in particular the distribution with heliographic latitude of the solar wind mass flux. This is obtained from an intensity map of the sky Lymanα emission, which reflects the shape of the ionization cavity carved in the flow of interstellar H atoms by the solar wind. The methodology, inversion procedure and related complications are described. The subject of latitude variation of the solar wind is shortly reviewed: earlier Lymanα results from Prognoz in 1976 are confirmed by Ulysses. The importance of the actual value of the solar wind mass flux for the equation of dynamics in a polar coronal hole is stressed. The instrument is composed of one electronic unit commanding two identical Sensor Units, each of them allowing to map a full hemisphere with a resolution of 1°, thanks to a two-mirrors periscope system. The design is described in some details, and the rationale for choice between several variants are discussed. A hydrogen absorption cell is used to measure the shape of the interplanetary Lymanα line and other Lyman α emissions. Other types of observations are also discussed : the geocorona, comets (old and new), the solar corona, and a possible signature of the heliopause. The connexion with some other SOHO instruments, in particular LASCO, UVCS, SUMER, is briefly discussed.

Effect of local interstellar medium hydrogen fractional ionization on the distant solar wind and interface region

Abstract: The paper investigates the influence of the local interstellar medium (LISM) proton number density on the gasdynamics of LISM / solar wind interaction. It uses the self-consistent axisymmetric model of Baranov and Malama (1993) for a constant value of the LISM neutral hydrogen number density (nH∞ = 0.14 cm−3). It is shown that the flow structure is asymmetric relative to the upwind and downwind directions. Numerical results are presented for four values of the proton number density in the LISM: np∞ = 0.005; 0.025; 0.1 and 0.28 cm−3. The results are given along the axis of symmetry only (in upwind and downwind directions). Velocity, number density, and temperature distributions of the plasma component as well as of the H atoms of the LISM are presented. It is shown that the influence of H atoms, penetrating from the LISM into the solar system on the solar wind may be strong enough to be observed by the “Voyager” spacecraft. The results show that the number density of the LISM's plasma component as well as of the solar wind has very large gradients in the interface region (between the bow and termination shocks). This effect may be very important for the interpretation of the kHz radiation detected by “Voyager”. Moreover, the asymmetric (in upwind and downwind directions) distributions of H atom number density, bulk velocity, and temperature may be observed on the basis of the scattered solar Lyman alpha radiation data.

Weak pitch angle scattering of few MV rigidity ions from measurements of anisotropies in the distribution function of interstellar pickup H

Abstract: The distribution function of interstellar pickup hydrogen is measured with the SWICS instrument on Ulysses at high heliographic latitudes, over a broad range of velocities, including those below that of the solar wind. It is found that these few MV rigidity protons exhibit a pronounced inward radial streaming in the frame of the solar wind, suggesting that neither instabilities generated by the pickup ions nor ambient turbulence is effective in scattering and isotropizing these particles. These results have implications for theories for the instabilities associated with pickup ions and for the propagation of low rigidity particles in the solar wind.

Propagation of solar oscillations through the interplanetary medium

Abstract: Time-series analysis of the fluxes of interplanetary charged particles measured by the Ulysses and Voyager spacecraft reveals many periodic components. From 1 to 140 µHz, the spectral components are consistent with those estimated (but not confirmed) for gravity-mode oscillations of the Sun: from 1,000 to 4,000 µHz, the spectral lines closely match the frequencies of known solar pressure modes. These concordances imply that the solar wind and the interplanetary magnetic field transmit solar oscillations and thus might be used to probe the interior structure of the Sun.

Dissipation of pickup‐induced waves: A solar wind temperature increase in the outer heliosphere?

Abstract: The deposition of energy into the solar wind by the pickup of interstellar neutrals is due to both the creation of hot, nonthermal ions and the associated generation of low frequency magnetohydrodynamic (MHD) waves. Dissipation of some fraction of the free wave energy released by ion pickup and isotropization is possible through nonlinear turbulent processes which may lead to heating of the core thermal solar wind proton distribution. Simple energy budget arguments are utilized to show that pickup ion generated wave dissipation may play a significant role in determining the solar wind radial temperature profile in the outer heliosphere. In particular, depending on the density of interstellar hydrogen in the heliosphere, there will be some radial distance beyond which the thermal solar wind core temperature increases steadily until the termination shock. Existing Pioneer and Voyager temperature profiles are consistent with this interpretation.

The solar WIND and suprathermal ion composition investigation on the WIND spacecraft

Abstract: The Solar Wind and Suprathermal Ion Composition Experiment (SMS) on WIND is designed to determine uniquely the elemental, isotopic, and ionic-charge composition of the solar wind, the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 175 kms−1 (protons) to 1280 kms−1 (Fe+8), and the composition, charge states as well as the 3-dimensional distribution functions of suprathermal ions, including interstellar pick-up He+, of energies up to 230 keV/e. The experiment consists of three instruments with a common Data Processing Unit. Each of the three instruments uses electrostatic analysis followed by a time-of-flight and, as required, an energy measurement. The observations made by SMS will make valuable contributions to the ISTP objectives by providing information regarding the composition and energy distribution of matter entering the magnetosphere. In addition SMS 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; and (vii) the physics of the pick-up process of interstellar He as well as lunar particles in the solar wind, and the isotopic composition of interstellar helium.

C+ pickup ions in the heliosphere and their origin

Abstract: C + pickup ions were discovered with the solar wind ion composition spectrometer flying on Ulysses. Whereas the other nonlocally occurring pickup ions are produced from the interstellar gas penetrating deep into the heliosphere, C + comes from an inner source which is located at a solar distance of a few AU and extends over all heliospheric latitudes investigated so far. The total production of C + , N + , and O + by this inner source is of the order of 10 −3 relative to the total production of O + from the interstellar gas in the heliosphere. Thus the inner source does not significantly contribute to oxygen or nitrogen in the anomalous cosmic rays (ACR), but its contribution to ACR carbon may not be negligible. We propose that the inner source material is carbon compounds evaporating from grains. At this time, the evidence points to interstellar grains as the major source, but we do not want to exclude yet a contribution from grains of solar system origin.

Turbulent heating and temperature evolution in the solar wind plasma

Abstract: We calculate the turbulent dissipation rate of incompressive hydromagnetic fluctuations and the resulting radial evolution of temperature in the solar wind using generalizations of Kolmogorov and Kraichnan MHD turbulence phenomenologies that include the suppression of dissipation by high cross helicity. The results for the temperature evolution are compared to a variety of data sets to test the phenomenologies over a wide parameter range. Motivated by the observations, we use different power laws in radius for the amplitudes of Alfvenic and nonAlfvenic fluctuations to determine the cascade rates. To explain the observations using Kolmogorov-like models, we found it necessary to suppress the dissipation rates for the high cross helicity streams even further than predicted by simple models ; this may be due to the nonequilibrium nature of the spectrum or to other causes as yet unknown. The Kolmogorov-like model gives rise to a significant amount of turbulent heating, implying that turbulent heating, while likely dominant only in the inner heliosphere, may be competitive with heating by shocks and the assimilation of interstellar pickup ions in the outer heliosphere. In contrast, the generalized Kraichnan phenomenology yields less turbulent heating than the Kolmogorov-like model and seems inadequate to explain the observations. We conclude that while no existing turbulence model adequately explains the observed radial dependence of temperature in the solar wind, there appears to be sufficient energy available for turbulent heating to contribute significantly, even in the outer heliosphere.

Interpretation and consequences of large-scale magnetic variances observed at high heliographic latitude

Abstract: We consider recent Ulysses observations of the large-scale variances in the transverse components of the interplanetary magnetic field. A previously-suggested theory is shown to provide a good fit to the observed spatial variation and level of the fluctuations. The transport of cosmic rays in the heliosphere will be significantly affected by these fluctuations. In addition to impeding the inward, radial diffusive and drift access of cosmic rays over the poles, the magnetic fluctuations imply a large latitudinal diffusion, caused primarily by the field-line mixing, or random walk.

Evidence for a solar wind slowdown in the outer heliosphere

Abstract: Voyager 2 and IMP 8 plasma data are used to look for the predicted slowdown of the solar wind with heliospheric distance. Decreases of roughly 7% in the radial velocity and of the same order in the flux are found if the Voyager 2 and IMP 8 velocities are normalized to agree in the inner heliosphere. This decrease is consistent with a pickup ion density equal to 8% of the total ion density, similar to predictions and other determinations of this density. Comparison with published model results allows us to infer an interstellar neutral density of 0.05 cm−3.

Injection and acceleration of interstellar pickup ions at the heliospheric termination shock

Abstract: We have used a one-dimensional hybrid code (macro-ions, massless electron fluid) in order to study the interaction of an interstellar pickup ion distribution with the heliospheric termination shock. The shock is generated by reflecting the solar plasma at a rigid wall. The interstellar pickup ions are additional populations modeled as spheres in velocity space with radii given by the solar wind speed, comoving with the solar wind. The pickup ions are located on the outer shell of the spheres. We have determined the reflection rates of the pickup ions, which have been defined as the ratio of the reflected to the incident pickup ions at the shock. The dependence of these reflection rates on the shock normal angle Θ Bn and on an upstream imposed turbulence has been investigated. No backscattered pickup ions are found for Θ Bn greater than 70° and the reflection rates decrease with increasing level of upstream imposed turbulence. The dependence of the reflection rate on the ratio of the upstream pickup proton density to the upstream solar wind density has been investigated. Since this ratio is proportional to the heliospheric distance of the termination shock we have been able to investigate the reflection rates of the pickup ions at different heliospheric locations of the termination shock. Based on these hybrid simulations a model for the acceleration of anomalous component of the cosmic rays has been developed which is able to explain the differential flux of anomalous helium at the termination shock needed in modulation calculations to fit observations in the inner heliosphere. In this model we have not included the influence of the anomalous component on the shock structure. From comparison with modulation calculations it is concluded that the location of the termination shock is at distances between 80 and 120 AU.

Corotating variations of cosmic rays near the South heliospheric pole.

Abstract: Three-dimensional simulations of the heliospheric modulation of galactic cosmic ray protons show that corotating variations in the intensity can persist to quite high heliographic latitudes. Variations are seen at latitudes considerably higher than the maximum latitude extension of the heliographic current sheet, in regions where the solar wind velocity and magnetic field show no significant variation. Similar conclusions may apply also to lower energy particles, which may be accelerated at lower latitudes. Cosmic ray variations caused by corotating interaction regions present at low heliographic latitudes can propagate to significantly higher latitudes.

Simulation of magnetic cloud propagation in the inner heliosphere in two-dimensions: 1. A loop perpendicular to the ecliptic plane

Abstract: We present results of simulations of a magnetic cloud's evolution during its passage from the solar vicinity (18 solar radii) to approximately 1 AU using a two-dimensional MHD code. The cloud is a cylinder perpendicular to the ecliptic plane. The external flow is explicitly considered self-consistently. Our results show that the magnetic cloud retains its basic topology up to 1 AU, although it is distorted due to radially expanding solar wind and magnetic field lines bending. The magnetic cloud expands, faster near the Sun, and faster in the azimuthal direction than in the radial one; its extent is approximately 1.5–2× larger in the azimuthal direction. Magnetic clouds reach approximately the same asymptotic propagation velocity (higher than the background solar wind velocity) despite our assumptions of various initial conditions for their release. Recorded time profiles of the magnetic field magnitude, velocity, and temperature at one point, which would be measured by a hypothetical spacecraft, are qualitatively in agreement with observed profiles. The simulations qualitatively confirm the behavior of magnetic clouds derived from some observations, so they support the interpretations of some magnetic cloud phenomena as magnetically closed regions in the solar wind.

Motion of the termination shock in response to an 11 Year variation in the solar wind

Abstract: A two-dimensional hydrodynamic numerical model was used to study the motion of the termination shock in response to an 11 year variation in the solar wind ram pression. For a total variation in the ram pressue by a factor of 2, a termination shock at 89 AU was found to move inward and outward about +/- 8% of its distance with a typical velocity of 12 km/sec. This movement may be understood in terms of the various time scales associated with the response of the termination shock and heliopause to variations in the solar wind ram pressure.

ULYSSES Observations of Latitude Gradients in the Heliospheric Magnetic Field: Radial Component and Variances

Abstract: The radial component of the magnetic field at Ulysses, over latitudes from −10° to −45° and distances from 5.3 to 3.8 AU, compares very well with corresponding measurements being made by IMP-8 in the ecliptic at 1AU. There is little, if any, evidence of a latitude gradient. Variances in the field, normalized to the square of the field magnitude, show little change with latitude in variations in the magnitude but a large increase in the transverse field variations. The latter are shown to be caused by the presence of large amplitude, long period Alfvenic fluctuations. This identification is based on the close relation between the magnetic field and velocity perturbations including the effect of anisotropy in the solar wind pressure. The waves are propagating outward from the Sun, as in the ecliptic, but variance analysis indicates that the direction of propagation is radial rather than field-aligned. A significant long-period component of > 10 hours is present.

Locations of the termination shock and the heliopause

Abstract: The locations of the termination shock and the heliopause are restudied by taking into account the effects of pickup protons. The study uses available plasma and magnetic field data from Voyagers over a 14-year period (1978-1991) and Voyager observations of the 1992-1993 radio emission event. Outside 30 AU, pickup protons have a significant influence on dynamical structures of the outer heliosphere. The solar wind is treated as a mixture of electrons, solar wind protons and interstellar pickup protons. If the magnitude of the interstellar magnetic field B{sub int} is given, one can quantitatively study the motion and location of the termination shock. We find that the location is anticorrelated with the sunspot number. The absolute mean of the shock speed is 19 km/s, and the quadratic mean of the shock speed is 24 km/s. Because B{sub int} is poorly known, additional information is needed in studying the termination shock. Cummings et al. (1994) have used observations of anomalous cosmic rays to estimate the location of the shock. The observations of the 1991 global merged interaction region (GMIR) and GMIR shock and the 1992-1993 radio emission event provide another handle for the study of the termination shock and the heliopause. Aftermore » its penetration through the termination shock, the GMIR shock continued to propagate in the subsonic region of the solar wind and eventually interacted with the heliopause. This interaction produced a transmitted shock propagating outward in the interstellar medium and a reflected shock propagating inward toward the Sun in the subsonic solar wind. The plasma frequencies behind the reflected and the transmitted shocks can be responsible for the 2- and 3-kHz radio emission, respectively. We assume that the impingement of the GMIR shock at the heliopause occurred at the time when Voyagers started receiving the radio emissions.« less

Cosmic ray decreases and solar wind disturbances during late October 1989

Abstract: We describe the interplanetary phenomena (energetic particles, solar wind plasma, and magnetic field) seen at Interplanetary Monitoring Platform 8 (IMP 8) and at International Cometary Explorer (ICE), located 65 deg west of IMP 8, during the period October 19-31, 1989, when neutron monitors observed three ground level events originating in one active region when it was in the longitude range E09 deg to W57 deg. At least four shocks, associated with energetic particle enhancements, which can be attributed to a sequence of coronal mass ejections from the same active region, were seen at both spacecraft. An additional shock was observed only at ICE late in this period when the active region was behind the west limb. Considering all the data (which unfortunately suffer from large gaps), it appears that the ejecta associated with the shocks were detected only when the spacecraft and solar source longitude were separated by less than 50 deg. The shocks extended over a greater range of longitudes. The cosmic ray record at Earth is consistent with this picture such that only the first two shock-associated cosmic ray decreases had the signature expected for intercepting ejecta material. This same time period was also examined by Bavassano et al. (1994). However, we do not agree with their conclusion that 'magnetic clouds' extending at least 75 deg from the source longitude were present.

Results of the Ulysses fast latitude scan : magnetic field observations

Abstract: The rapid crossing of the solar equatorial region by Ulysses as it returned from the south pole resulted in 7 crossings of the heliospheric current sheet between 10°S and 20°N and 10 distinct solar wind interaction regions between 18°S and 22°N. Both the extent of the current sheet and the latitude interval containing the interaction regions are a factor of ≈ 2 less than were observed by Ulysses when it left the equatorial region in 1993. A map of the current sheet in heliographic latitude and Carrington longitude reveals two folds corresponding to 4 magnetic sectors. The coronal holes associated with the sectors, the interaction regions and high-speed streams have been identified. Two sectors were associated with a pair of asymmetrically-placed polar coronal holes whereas the other two sectors coincided with a pair of near-equatorial coronal holes on opposite sides of the equator.