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Interplanetary coronal mass ejections (ICMEs) are a significant feature of the heliospheric environment and the primary cause of adverse space weather at the Earth. ICME propagation, and the evolution of ICME magnetic field structure during propagation, are still not fully understood. We analyze the magnetic field structures of 18 ICME magnetic flux ropes observed by radially aligned spacecraft in the inner heliosphere. Similarity in the underlying flux rope structures is determined through the application of a simple technique that maps the magnetic field profile from one spacecraft to the other. In many cases, the flux ropes show very strong underlying similarities at the different spacecraft. The mapping technique reveals similarities that are not readily apparent in the unmapped data and is a useful tool when determining whether magnetic field time series observed at different spacecraft are associated with the same ICME. Lundquist fitting has been applied to the flux ropes and the rope orientations have been determined; macroscale differences in the profiles at the aligned spacecraft may be ascribed to differences in flux rope orientation. Assuming that the same region of the ICME was observed by the aligned spacecraft in each case, the fitting indicates some weak tendency for the rope axes to reduce in inclination relative to the solar equatorial plane and to align with the solar east-west direction with heliocentric distance., Comment: 35 pages, 10 figures

This report assesses the current status of research relating the origin at the Sun, the evolution through the inner heliosphere and the effects on the inner heliosphere of the interplanetary counterparts of coronal mass ejections (ICMEs). The signatures of ICMEs measured by in-situ spacecraft are determined both by the physical processes associated with their origin in the low corona, as observed by space-borne coronagraphs, and by the physical processes occurring as the ICMEs propagate out through the inner heliosphere, interacting with the ambient solar wind. The solar and in-situ observations are discussed as are efforts to model the evolution of ICMEs from the Sun out to 1 AU.

While interplanetary coronal mass ejections (ICMEs) are understood to be the heliospheric counterparts of CMEs, with signatures undeniably linked to the CME process, the variability of these signatures and questions about mapping to observed CME features raise issues that remain on the cutting edge of ICME research. These issues are discussed in the context of traditional understanding, and recent results using innovative analysis techniques are reviewed.

In February 2004 the Ulysses spacecraft had its second flyby at Jupiter at 0.8 AU distance from the planet. Twenty-eight dust streams emanating from the jovian system were measured between November 2002 and August 2005 while the spacecraft was within 4 AU of the planet, scanning jovigraphic latitudes from + 75 ∘ to - 25 ∘ . The highest dust fluxes were measured in mid 2004 at the passage of the equatorial plane of the planet when more than 2000 impacts per day were measured. The grain impact direction is correlated with the polarity and strength of the interplanetary magnetic field. At high jovigraphic latitudes, the impact rates show a periodicity of 26 days, closely matching the solar rotation period, while at the jovian equator the streams fluctuate with twice this period. The 14-day subharmonic streams alternate in arrival direction and are correlated with the pointing of the interplanetary magnetic field. Dust fluxes measured above and below the equatorial plane roughly decrease with the inverse square of the distance from the planet while along the equatorial plane dust fluxes are enhanced by up to 2 orders of magnitude.

From all the transient events identified in interplanetary space by in-situ measurements, Magnetic Clouds (MCs) are among the most intriguing ones. They are a special kind of Interplanetary Coronal Mass Ejections (ICMEs), characterized by a well-defined magnetic field configuration. We use a list of 40 MCs detected by Ulysses to study bidirectional flows of protons in the 0.5 MeV energy range. Solar wind ions are also analysed in order to compare cloud to non-cloud ICMEs.The enhancement in freezing-in temperatures inside the clouds, obtained with data from the SWICS instrument, provides insights into processes occurring early during the ejection of the material and represents a complementary tool to differentiate cloud from non-cloud ICMEs. At higher energies, directional information for protons obtained with the EPAC instrument allows a comparison with previous results concerning bidirectional suprathermal electrons. The findings are qualitatively comparable. Apparently, the portion of bidirectional flows inside magnetic clouds is neither heavily dependent on distance from the Sun nor on parameters obtained from a flux rope model.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The first passage of the Ulysses spacecraft to high latitudes was during the declining phase of solar cycle 22. The recent second passage to high latitudes was close to the maximum of solar cycle 23. The axis of the dipolar component of the Sun's magnetic field was close to 90° from the spin axis, and the coronal neutral line extended up to high latitudes. A variable but generally slow solar wind was observed all the way up to the highest latitudes reached by Ulysses, as was the sector structure of the magnetic field. The high-latitude heliosphere was populated with intensities of energetic particles with energies around 1 MeV several orders of magnitude above background. We show how the changes in the Sun's magnetic field, the coronal holes, and the configuration of the heliosphere could be responsible for the differences between particle observations in the two orbits.

Observations during the recent ascent of Ulysses to the south polar region are reported. Large variations in field magnitude are associated principally with solar wind interaction regions. The observed spiral angle agrees reasonably well with the Parker model. The magnetic flux, the product of the radial field component and the square of the radial distance (r² BR), is independent of latitude implying non-radial expansion of the solar wind. Two magnetic sectors are present up to a latitude of ≈ −78° above which a single negative (inward) polarity is observed consistent with the polar field not yet having reversed. Crossings between sectors, extrapolated back to the sun, appear consistent with a single warped current sheet tilted slightly to the rotation axis. Field lines in the polar region passing near the current sheet originate at low latitudes. They provide access of high energy solar particles to the polar region.

Charge state distributions of heavy solar wind ions measured in interplanetary space can be used to probe the physical conditions in the solar corona. This paper presents a study of the charge state distributions and the magnetic topology of 56 coronal mass ejections (CMEs) observed in interplanetary space by the Ulysses spacecraft. The analysis of the data from the Solar Wind Ion Composition Spectrometer (SWICS) instrument and the Vector Helium Magnetometer (VHM) experiment onboard Ulysses shows a clear correlation between the charge state distributions and the magnetic topology of CMEs. Almost all CMEs whose charge state distributions are shifted to higher charge states with respect to the ambient solar wind have the structure of magnetic clouds, whereas CMEs with the same charge state distributions as the surrounding solar wind do not show magnetic cloud structure. This correlation is found for CMEs observed at low, mid, and high solar latitudes. On the basis of the numerical solution of the ionization/recombination equations for oxygen and silicon, it is investigated which changes of the electron temperature, electron density, and the speed of the ions in the source region of the CMEs can reproduce the observations. It is shown that the main reason for the observed enhancement of higher charge states in the cloud CMEs is an increased electron temperature. However, the evolution of the density and velocity of the CMEs before the charge states freeze in cannot be neglected.

Pioneer and Ulysses observations of energetic particles and solar wind plasma and magnetic fields are analyzed to study particle transport in corotating interaction regions (CIRs) and near stream interfaces (SIs). Energetic particle diffusion with a lowered coefficient near the SIs as compared with the free solar wind may account for the energetic particle profiles in CIRs and for the modulation of Jovian electrons. Our analyses include examination of the magnetic power and variances perpendicular and parallel to the magnetic field for a range of wave numbers and for a range of conditions within two CIRs. Since the magnetic field immediately on either side of a SI, but near it, is not connected to either the forward shock or reverse shock, it is the cross-field motion of the energetic particles that is relevant. Since the cross-field transport is thought to be related to field line mixing, or random walk, we examined magnetic field fluctuations normal to the average field to determine whether any signature of reduced perpendicular particle transport could be found. Evidence consistent with reduced particle transport near the SI was indeed found when we examined time series of the 1-min averages of the magnetic field components. A planar magnetic structure was associated with the trailing unshocked layer following the SIs (i.e., SI to SI + 12 hours) and also with the entire CIRs, but it was not present in the free solar wind. We have quantitatively examined the effects of shear and compression on particle transport and conclude that the effects of shear and compression reduce particle transport in CIRs and in the vicinity of SIs.

We present observations of energetic ions from the Cosmic Ray and Solar Particle Investigation (COSPIN) and Heliosphere Instrument for Spectra Composition and Anisotropy at Low Energy (HISCALE) instruments on board the Ulysses spacecraft. We examine in detail the onset of energetic ions observed during the March 1991 series of solar events. Active region 6555, at E28 at 2247 UT on March 22, 1991 (day 81), was most likely responsible for the high-energy protons subsequently seen at Ulysses. A slow increase in the high-energy (∼50 MeV) proton intensity, made up of many small but rapid intensity increases, began around 9 hours after the onset of the event, taking 1.5 days to reach maximum intensity. On the flank, and in front of a coronal mass ejection (CME), coming from a previous event, we observed a region with a drop in the magnetic field strength. This region was populated with hot shocked plasma and, owing to the low magnetic field pressure, had an ion plasma beta >1. Mirror mode waves, with discontinuities appearing at the edges of the waves, produced a larger-than-average number of magnetic field discontinuities, a large fraction of the discontinuities being aligned with their normals oriented along the radial direction, suggesting that they were being convected outward by the CME. These discontinuities acted as a series of barriers to the propagation of the energetic solar particles coming from the solar event, delaying substantially the onset of the particle event at Ulysses.

In this paper, magnetic and plasma measurements are used to analyze 17 interplanetary coronal mass ejections (CMEs) identified by Ulysses during its in-ecliptic passage to Jupiter. We focus on the expansion characteristics of these CMEs (as inferred from the time rate of change of the velocity profiles through the CMEs) and the properties of 14 forward shocks unambiguously associated with these CMEs. We highlight radial trends from 1 to 5.4 AU. Our results indicate that the CMEs are generally expanding at all heliocentric distances. With regard to the shocks preceding these ejecta, we note the following: (1) There is a clear tendency for the shock speed (in the upstream frame of reference) to decrease with increasing heliocentric distance as the CMEs transfer momentum to the ambient solar wind and slow down; (2) 86% of the shock fronts are oriented in the ecliptic plane such that their normals point westward (i.e., in the direction of planetary motion about the Sun), (3) 86% of the shocks are propagating toward the heliographic equator; and (4) no clear trend was found in the strength of the shocks versus heliocentric distance. These results are interpreted using simple dynamical arguments and are supported by fluid and magnetohydrodynamic (MHD) simulations.

Ulysses encountered two separate sequences of corotating interaction regions (CIRs) in 1992–3 and 1996–7 when the spacecraft was in the southern and northern solar hemispheres, respectively. We have examined magnetometer data from one event observed in each hemisphere. Using two separate analytical methods we provide evidence for the magnetic field vectors within these CIRs being strongly confined to a series of near-parallel planes. The distribution of the field within the interaction region is characteristic of that observed in planar magnetic structures. This planar order is evident over both small (3-hour) and large (whole event) scales. The CIRs display opposed north-south tilts that are consistent with previous authors' analysis of solar wind plasma data. These results are in direct agreement with the tilted dipole model of three-dimensional corotating stream interactions.

SUMMARY We develop statistical testing methodology for closely spaced spectral lines based on multitaper spectrum estimates and apply it to a time series of solar magnetic field magnitude data recorded by the Ulysses spacecraft. The test is formulated through complex-valued weighted least squares. Using this test in combination with the test for well-separated lines, we can accurately detect the solar equatorial rotation frequency of the sun, and its harmonics, from data recorded by Ulysses’s magnetometer at solar mid-latitudes; this is a potentially important result for solar physicists, since it has implications for the structure and dynamics of magnetic fields in the solar corona.

We examine the relation between the current sheet as derived from observations of the Sun's neutral line, and recurrent particle increases associated with co-rotating interactions regions (CIR) at 4 to 5 AU radial distance as observed by the Ulysses spacecraft during its rst out-of- ecliptic orbit around the Sun. We compare observations during the ascent to high southern latitudes, close to so- lar maximum, with observations during the return to the ecliptic from high northern latitudes, close to solar mini- mum, when the spacecraft was passing from the streamer belt to high-speed solar wind flow or vice-versa every solar rotation, and when regular recurrent particle increases were observed. Although conditions are very dierent, we show that the position of the Sun's neutral line, propagated out to the position of the spacecraft, can be used to explain the recurrence of the particle increases observed at 4-5 AU at Ulysses.

The Whole Sun Month campaign (August 10 to September 8, 1996) brought together a wide range of space-based and ground-based observations of the Sun and the interplanetary medium during solar minimum. The wealth of data collected provides a unique opportunity for testing coronal models. We develop a three-dimensional magnetohydrodynamic (MHD) model of the solar corona (from 1 to 30 solar radii) applicable to the WSM time period, using measurements of the photospheric magnetic field as boundary conditions for the calculation. We compare results from the computation with daily and synoptic white-light and emission images obtained from ground-based observations and the SOHO spacecraft and with solar wind measurements from the Ulysses and WIND spacecraft. The results from the MHD computation show good overall agreement with coronal and interplanetary structures, including the position and shape of the streamer belt, coronal hole boundaries, and the heliospheric current sheet. From the model, we can infer the source locations of solar wind properties measured in interplanetary space. We find that the slow solar wind typically maps back to near the coronal hole boundary, while the fast solar wind maps to regions deeper within the coronal holes. Quantitative disagreements between the MHD model and observations for individual features observed during Whole Sun Month give insights into possible improvements to the model.

In this report, we summarize measurements made by the plasma experiment on the Ulysses spacecraft during the period designated as “Whole Sun Month” (WSM, August 10 to September 8, 1996). This interval coincided with the return of solar wind variability at Ulysses. Ulysses was located at ∼ 28°N heliographic latitude, at a heliocentric distance of 4.25 AU, and on the opposite side of the Sun from Earth. In particular, we explore the evolution of the solar wind between the Sun and Ulysses for several rotations surrounding WSM. Specifically, we map Ulysses measurements back toward the Sun by applying a two-dimensional inverse MHD algorithm. This approach is compared with the commonly used constant speed (or ballistic) approximation. We find that the MHD mapping technique produces substantially better results when compared with solar observations. Both the Ulysses MHD-mapped results and the solar observations are consistent with a picture of a modestly tilted streamer belt (< 10°) that was deformed northward by an active region at 240° –; 270° longitude.

The episode of intense solar activity on 4 and 6 November 1997 resulted in large and extended particle events observed by the Ulysses and WIND spacecraft. Ulysses was at a heliocentric distance of 5.34 AU, very close to the solar equator and 100° west in heliolongitude from earth. WIND was near the earth at 0.99 AU from the Sun and in the ecliptic plane. Both spacecraft detected particle events and magnetic field structures related to this intense activity. A likely scenario for these particle events is proposed. The differences in the particle intensity profiles observed by both spacecraft are explained in terms of their location with respect to the solar activity site, the existence of interplanetary structures traveling towards the spacecraft, and the nature of particle transport from the source up to the two spacecraft.

Data obtained by instruments on the Ulysses spacecraft during its rapid sweep through >90° of solar latitude, crossing the solar equator in early 1995, were combined with data obtained near Earth by the Wind spacecraft to study the spatial structure of the solar wind and to compare to different models of the interplanetary magnetic field derived from solar observations. Several different source-surface models matched the double sinusoidal structure of the heliospheric current sheet (HCS) but with differences in latitude as great as 21°. The source-surface model that included an interplanetary current sheet gave poorer agreement with observed current-sheet crossings during this period than did the other source-surface models or an MHD model. The differences between the calculated and observed locations of the HCS were minimized when 22° of solar rotation was added to the constant-velocity travel time from the source surface to the spacecraft. The photospheric footpoints of the open field lines calculated from the models generally agreed with observations in the He 10,830 A line of the locations of coronal holes with the exceptions that (1) in some places, open field lines originated outside the coronal hole boundaries and (2) the models show apparently closed-field regions just inside some coronal hole boundaries. The patterns of mismatches between coronal hole boundaries and the envelopes of open field lines persisted over at least three solar rotations. The highest-speed wind came from the polar coronal holes, with the wind originating deeper within the hole being faster than the wind coming from near the hole boundary. Intermediate and slow streams originated in smaller coronal holes at low latitudes and from open field regions just outside coronal hole boundaries. Although the HCS threaded regions of low speed, low helium abundance, high ionization temperature, and a high ratio of magnesium to oxygen densities (a surplus of an element with low first-ionization potential), there was a great deal of variation in these parameters from one place to another along the HCS. The gradient of speed with latitude varied from 14 to 28 km s−1 deg−1.

An overall profile of plasma wave activity in a frequency range of 0.2 to 448 Hz in the solar wind is presented using 6 years of Ulysses data which cover a large range of heliographic latitudes (0° to ±80° ) at distances from 1 to 5 AU from the Sun. The spacecraft has continuously observed wave activity with peak power below the local electron cyclotron frequency f ce . Four distinct types of fluctuation phenomena have been observed: (1) enhanced electromagnetic fluctuations associated with the interplanetary shocks and heliospheric current sheet crossings and other solar wind turbulence; (2) enhanced electromagnetic fluctuations associated with compression regions of high-speed stream interfaces, which were observed in periods of increasing solar wind velocity; (3) electric fluctuations associated with the expanding solar wind, which were observed in periods of decreasing solar wind velocity; and (4) enhanced electric fluctuations in the high-latitude fast solar wind plasma. The fourth type of wave activity was observed nearly continuously with the relative power observed peaked near the local f ce . The first three types of waves were observed in the heliomagnetic streamer belt flows, where the spacecraft frequently encountered enhanced solar wind turbulence, interplanetary shocks, and current sheet crossings. The electromagnetic wave bursts (types 1 and 2) are likely to be whistler mode. The occurrences of apparently electrostatic waves during periods of expanding solar wind are coincident with significant reductions in the electron heat flux intensity. The generation mechanism of these electrostatic waves is still under investigation, but the observations may imply that these waves reduce the intensity of the heat flux through enhanced wave particle scattering associated with a heat flux instability.

The Ulysses spacecraft encountered 160 interplanetary shock waves between the time of its launch in October 1990 and the end of 1993 when it reached 48° S heliographic latitude. The onboard radio and plasma wave instrument observed many plasma waves associated with these shocks. Electrostatic waves at frequencies between the ion and electron plasma frequencies are observed intermittently throughout the solar wind but are often strongly enhanced near the shocks. These waves are usually interpreted as ion acoustic waves that have been Doppler shifted to the observed frequencies. They show very diverse characteristics in their amplitude and in their temporal behavior relative to the time of the shock passage at Ulysses. They are most likely to occur within a few minutes of shock passage, but on average they are enhanced above background levels for several hours before and after passage of the shock. The temporal behavior of the probability of occurrence of these waves is roughly symmetric relative to the time of shock passage and furthermore is quite similiar for quasi-parallel and quasi-perpendicular shocks and for forward and reverse shocks. These waves are correlated with several of the local plasma parameters measured by the Ulysses plasma instrument, most strongly with Te/Tp, the ratio of electron temperature to proton temperature, and with the electron heat flux. There is no significant correlation of the waves with the upstream plasma β or the shock strength. The similiarity of the quasi-parallel and quasi-perpendicular cases implies that the mechanism for wave generation is not sensitive to θBn, the angle between the upstream magnetic field and the shock normal. Examination of the particle distribution function at the shocks indicate that beams in the proton distribution function and enhanced electron heat flux may contribute to driving the waves unstable, particularly when Te/Tp is small.

After passing through the northern polar regions of the heliosphere during the summer of 1995, the Ulysses spacecraft has been gradually returning towards lower equatorial latitudes, reaching 30°N in August 1996 at about which time low speed solar wind from the streamer belt was once again observed. This paper reports on the Ulysses magnetic field observations, beginning from this time, concentrating on encounters with the heliospheric current sheet. These encounters restarted at a latitude of 25.5°N, a higher latitude than might be expected at solar activity minimum. We show that this early reappearance was due to a northward deflection of the current sheet caused by a long-lived active region at the corresponding heliographic longitude in the photosphere.

We have correlated the ∼1 MeV proton intensity (J) measured at corotating reverse shocks detected by Ulysses in the southern hemisphere with two parameters that characterise the strength of the shock. Between 6°–29°S J is essentially independent of the shock strength, whereas between 29°–41°S J is well correlated with the same. The poor correlation from 6°S to 29°S is attributed to variations in the background intensity caused by changes in solar activity. Our results also show that J is independent of the shock normal angle at all latitudes. We compensate for the effects of a fluctuating background by assuming that reverse shocks associated with two adjacent compression regions observed during a ∼26 day period accelerate particles out of the same seed population. The relation between the ratio of the proton intensities and the ratios of the shock parameters for such reverse shock-pairs indicates that the shock acceleration efficiency increases with the shock strength but is independent of the normal angle.

We present a study of whistler-mode wave generation and wave particle interaction in the vicinity of interplanetary shocks as observed by the Ulysses spacecraft. Generally the whistler-mode waves (measured in the frequency range 0.22–448 Hz) are observed downstream of the shocks where they persist for some hours. From the electron distribution functions (EDF) in the energy range 1.6 to 862 eV measured by the spacecraft, we compute the wave growth rate of the electromagnetic electron cyclotron and Landau instabilities for the case of oblique propagation of the waves with respect to the interplanetary magnetic field (IMF) B. In general, in agreement with the wave measurements, the instability grows mostly downstream of the shock fronts. Following the wave activity, velocity space diffusion of the electrons results in a marginally stable state with some sporadic fluctuations.

This study of whistler wave emission observed by the Ulysses Unified Radio and Plasma Wave (URAP) experiment between 1 and 5 AU is a complement to previous studies of whistler waves observed by the Helios spacecraft between 0.3 and 1 AU. The Helios spacecraft continuously detected a background of whistlers close to the Sun, and this background was found to decrease in intensity with larger heliocentric distance. Ulysses plasma wave observations confirm this trend. Within a heliocentric distance of approximately 2 AU, whistler waves are routinely observed. Beyond about 3 AU, the waves are usually observed only downstream of interplanetary shocks. Moreover, whistler waves are routinely observed within about 2 AU at all heliographic latitudes of the Ulysses trajectory (−80° to +80°). The combined observations from the Helios and Ulysses spacecraft suggest that whistler emission is always present in the solar wind, although at larger heliocentric distances the wave amplitudes are often below the thresholds of the URAP instrument. Observations throughout the first 5 years of the Ulysses mission show a clear correlation of whistler emission intensity with magnetic field strength, or gyrofrequency, such that increases in wave intensities coincide with increases in gyrofrequency. This correlation is especially evident in observations of interplanetary shocks and high-speed streams. A possible cause of this correlation is increased whistler wave growth due to enhanced electron temperature anisotropies in regions of compressed magnetic field. A shift of the background whistler spectrum as a function of gyrofrequency could account for the observed decrease in whistler amplitudes with increasing heliocentric distance.

Ulysses observations of the interplanetary magnetic field reveal well-ordered rotations on the timescale of several hours. These have been previously identified as arc-polarized Alfven waves. Rotational discontinuities (RDs) are often an integral part of the wave. This study focuses on a statistical description of these rotations (ARCs) in the ecliptic plane. It is found that (1) most ARCs are limited to 180° or less in rotation ; (2) these ARCs account for between 5 and 10% of the total data set ; (3) there appears to be no preferred helicity ; (4) the minimum-variance direction typically makes a large oblique angle with the average magnetic field (), while the intermediate-variance direction is loosely aligned with ; (5) most of the events display a small but significant nonzero magnetic field component in the direction of minimum variance ; (6) the cross helicity of the ARCs tends to be higher than during non-ARC intervals ; (7) there are 2.4 times more discontinuities during ARC intervals than during non-ARC intervals ; (8) essentially all ARCs are propagating outward in the rest frame of the solar wind plasma ; and (9) there is no simple relationship between the rate of occurrence of the ARCs and heliocentric distance. Comparing these results with the predicted signatures of a number of models, it is found that arc-polarized Alfven waves with embedded RDs propagating along the minimum-variance direction best fit the majority of events.

A study is presented of 153 fast shock waves and their relation to other large-scale features in the solar wind: corotating interaction regions (CIRs), interplanetary counterparts of coronal mass ejections (ICMEs) and the magnetic sector structure, observed by Ulysses from October 1990 to the south solar pass in the summer of 1994.

The plasma flow in Jupiter's magnetosphere observed during the Ulysses flyby is compared with previous Pioneer, Voyager and ground-based observations. These data show that near-rigid corotation is enforced in the inner magnetosphere, but that the azimuthal flow plateaus at 150-300 km s -1 in the middle magnetosphere plasma sheet beyond ∼20 R J . Such flows extend through the prenoon plasma sheet to ∼45 R J in the compressed magnetosphere observed by the Voyagers and to ∼70 R J in the expanded system observed by Ulysses. Higher speeds of ∼500 km s -1 occur in the postmidnight plasma sheet at 75-125 R J in Voyager data, while preliminary Ulysses evidence is presented for anticorotation in the dusk plasma sheet beyond ∼50 R J . In the outer magnetosphere the dawn and dusk flank flows are antisunward at several hundred kilometres per second, while in the prenoon sector the flow appears to depend magnetospheric state, being corotational at 250-600 km s -1 when compressed and anticorotational (and radially in) at ∼250 km s -1 when expanded. These observations are compared with theories proposed by Hill and Vasyliunas, augmented to include the effects of solar wind coupling. This model accounts qualitatively for many features, but not for the anticorotation flows observed. We also compare the flows with the bending of the magnetic field out of meridian planes. Given the subcorotation-anticorotation nature of the observed flow, a pervasive lagging configuration is expected. This accords with in situ field data, except for the dusk outer magnetosphere observed by Ulysses, where a leading configuration was observed in the presence of subcorotating (downtail) flow. We conclude that field bending due to the tail-magnetopause current system dominates that due to ionospheric coupling on the dusk flank.

The fundamental aim of the Ulysses space mission is to extend our understanding of the heliosphere into three dimensions. By April 1994, the spacecraft had reached a heliographic latitude of 60°S. Hourly averages of the Ulysses heliospheric magnetic field observations have been analyzed to determine to what extent the underlying field direction within 60° of the heliographic equator can be described by the Parker spiral model. At all latitudes from near the ecliptic southward to 60°S, the most probable value of the azimuthal orientation of the field lines remained in approximate agreement with the Parker model. Once Ulysses passed southward of the maximum latitude of the heliospheric current sheet at about 30°S it became possible to study the distribution of the azimuth angle in purely inward polarity southern hemisphere fields without the confusion between the northern and southern hemisphere sectors. This distribution is revealed to be highly asymmetric with a greater probability of observing field lines with an azimuth angle less tightly wound than the most probable angle. Comparison with near-ecliptic data showed a similar asymmetry in inward polarity field sectors while in outward polarity sectors there was an asymmetry in the opposite sense. We suggest that the asymmetry in the >30°S azimuth angle distribution arises due to the presence of long-period radially outward propagating Alfven waves in the solar wind flows originating from the southern polar coronal hole. In addition, from studying the meridional (north-south) orientation of the field lines we find that at south heliographic latitudes within about 25° of the equator there is a tendency in the Ulysses data set for the field lines to be on average deflected equatorward of their expected direction, most likely due to flow deflections associated with the interaction of high- and low-speed solar wind streams.

Between late 1993 and the middle of 1994, Ulysses stayed almost constantly within flows from the Sun's southern polar coronal hole, traveling from 44°S to 69°S heliolatitude and between 4.0 and 2.9 AU from the Sun. Magnetic field observations within this region reveal a very different medium from that at similar heliocentric distances near the ecliptic. Nearly 160 days of magnetic field data taken within this region are studied using structure functions. We demonstrate that the polar plasma flow is turbulent, with different populations of fluctuations on different scales. On spacecraft scales of 102–103 s, the fluctuations are indicative of inertial range turbulence and are intermittent, with a spectral slope near 1.7. On larger scales, the fluctuations are not intermittent, and the spectral slope is near 1. The similarities and differences between polar and near-ecliptic fluctuations are discussed.

Using Ulysses low energy telescope (LET) measurements of protons and alpha particles with energies of ∼1–5 MeV/n, we present first observations of transient energetic particle events in the high latitude heliosphere. Three transient particle events with gradual onsets and time durations of several days have been identified in the LET data at heliographic latitudes as high as ∼60°S, at radial distances from the Sun between 3.3–3.6 AU. No transient increases were observed polewards of 60°S. All three of the events were associated with passage of a coronal mass ejection (CME) over Ulysses, and two were associated with the newly identified type of forward/reverse shock pairs in the solar wind caused by over-expanding CMEs. The largest of the three transient events has also been observed at Earth's orbit, i.e. in the ecliptic. The observations show that energetic particles can be convected into the high latitude heliosphere through CMEs.

A variance analysis of high frequency, inertial range fluctuations in the polar magnetic field as recorded by the Ulysses spacecraft indicates that they are largely transverse to the ambient magnetic field direction and highly anisotropic. Despite large changes in the mean field direction caused by the presence of large amplitude Alfven waves, alignment of minimum variance vectors of 5 minute intervals of linearly detrended data with the mean field direction was good, with around 75% of minimum variance vectors lying within 26° of the mean field direction during a typical 5 day interval. Such fluctuations transverse to the mean field have anisotropies—the ratio of power transverse to the field to that parallel—of around 30. We find a small tendency for the field-transverse fluctuations to become more isotropic with distance. Intervals whose minimum variance directions are not field-aligned appear to be indicative of a significantly different type of fluctuations, with higher total variances and lower anisotropy.

We report the observations of an electron event at a heliolatitude of 73.8°S, the highest latitude interplanetary solar event reported to date. This event was detectable because the interplanetary background was not obscured by electrons produced in co- rotating interaction regions. The event was associated with an interplanetary type III burst and a solar active region located at 6°S as detected by the Nancay radioheliograph. The origin of the electrons is discussed. The observations favor an acceleration process in the low or middle corona followed by coronal propagation from the solar source to the highest heliolatitudes. This high latitude electron event presents rather different characteristics from those detected at low heliolatitudes.

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.

Data obtained during Ulysses' rapid northbound traverse across the heliographic equator provide evidence for predicted, opposed north-south tilts of corotating interaction regions formed from streams originating in the northern and southern solar hemispheres respectively. In both hemispheres, reverse waves that were propagating poleward were observed poleward of the latitudes where the fast-slow wind interaction occurred. Forward waves, on the other hand, were observed only within the low-latitude band of wind variability, consistent with the prediction of systematic, opposed tilts. However, the evidence for opposed north-south tilts within the low-latitude band of variability was less conclusive.

We present a study of whistler-mode wave generation and wave particle interaction in the vicinity of interplanetary shocks in and out of the ecliptic plane, as observed by the Ulysses spacecraft. We focus here on one shock in the ecliptic plane as a reference and three shocks obtained at −30, −54 and −55.4 degrees of heliographic latitude respectively. Generally the whistler-mode waves (measured in the frequency range 0.22–448 Hz) are observed downstream of the shocks where they persist for some hours. From the electron distribution functions in the energy range 1.6 to 862 eV, we compute the temperature anisotropy and the wave growth rate of the electromagnetic electron cyclotron instability for the case of parallel propagation of the waves with respect to the interplanetary magnetic field (IMF) B. In general, in agreement with the wave measurements, the instability grows only downstream of the shock fronts. Following the wave activity, velocity space diffusion of the electrons results in a marginally stable state with some sporadic fluctuations. Broadening of the wave reduced frequency range of the instability and an increase of the temperature anisotropy with latitude are observed.

Between April and November 1994 the Ulysses spacecraft explored heliographic latitudes above 60°S in the southern polar heliosphere and had returned to 20°S by February 1995. We have used hourly averages of the magnetic field measurements made by Ulysses to study the underlying heliospheric field direction. In contrast to data previously reported from lower latitudes, we find that above 60°S neither the mean nor the most probable azimuthal angle of the magnetic field agree with that predicted by the Parker model, the most probable angle being of the order of 24° more tightly wound than expected. The distribution of azimuth angles retains the high degree of asymmetry previously found at lower latitudes causing the mean angle to remain slightly less tightly wound than the prediction. In this high latitude region, the distribution of the meridional (north-south) angle is found to be symmetric with mean and most probable values close to the Parker prediction.

We report the first observations of Langmuir waves excited within magnetic holes, which are characterized by a depression of magnetic field strength. This phenomenon is very common in the solar wind. In addition to Langmuir waves, waves at a few kHz, which are typical of Doppler-shifted ion acoustic frequencies in the solar wind, and low frequency electromagnetic waves (below the electron cyclotron frequency) are sometimes observed simultaneously within the holes. In the holes with directional discontinuities at the boundary, the above plasma waves may occur at the edges of the holes. Possible physical mechanisms of the wave excitation are discussed.

The Ulysses magnetic field experiment has measured the heliospheric magnetic field in solar wind flows from the Sun's Southern polar coronal hole over a wide range of heliolatitudes and distances. We present an analysis of more than one year of data, covering a latitude range of 40° to 80°S and a distance range of 4.0 to 1.7 AU. We extend an earlier analysis of Ulysses magnetic field data and, by calculating structure functions, demonstrate that the spectrum of fluctuations in the magnetic field changed along the orbit of Ulysses within polar flows and that this change is a result of the variation in Ulysses' distance from the Sun, rather than its latitude. We interpret this change as being due to the development of turbulence in the polar solar wind.

We present here a preliminary analysis of observations of energetic ions during the first polar pass of the Ulysses spacecraft, concentrating mainly on the region where the spacecraft was continually immersed in high speed flow from the polar coronal hole. During the ascent to high latitudes, a single recurrent peak was observed once per solar rotation. From 70°S during ascent to 43°S during descent no major peaks were observed. Thereafter, two peaks per solar rotation were observed.

A solar wind disturbance produced by a fast coronal mass ejection, CME, that departed from the Sun on Feburary 20, 1994 was observed in the ecliptic plane at 1 AU by IMP 8 and at high heliographic latitudes at 3.53 AU by Ulysses. In the ecliptic the disturbance included a strong forward shock but no reverse shock, while at high latitudes the disturbance was bounded by a relatively weak forward-reverse shock pair. It is clear that the disturbance in the ecliptic plane was driven primarily by the relative speed between the CME and a slower ambient solar wind ahead, whereas at higher latitudes the disturbance was driven by expansion of the CME. The combined IMP 8 and Ulysses observations thus provide a graphic illustration of how a single fast CME can produce very different types of solar wind disturbances at low and high heliographic latitudes. Simple numerical simulations help explain observed differences at the two spacecraft.

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.