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Abstract. We show that the variations of the interplanetary magnetic field strength (B) over a 22-year period are tracked by the inverted profile of the cosmic ray density measured by neutron monitors. We suggest that global changes in the Sun's magnetic field are more important for longterm modulation than magnetic field enhancements resulting from the merging of high-speed flows and coronal mass ejections in the outer heliosphere. The unexpectedly close relationship that we find between the "tilt angle" of the heliospheric current sheet and the cosmic ray density away from solar minimum for both polarity states of the solar magnetic field may be accounted for by the anticorrelation between the cosmic ray density and field strength variations.

We examine the detailed relationship between recurrent cosmic ray depressions and corotating high‐speed streams in the inner heliosphere near the ecliptic plane using counting rates from anticoincidence guards of instruments on the IMP 8, Helios 1, and Helios 2 spacecraft. These rates indicate the density of >60 MeV/amu ions with reasonable time resolution (∼15 min) and high counting statistics. Essentially all corotating streams are accompanied by significant particle depressions. The particle decrease commences most frequently (∼63% of events) at the leading edge of the stream which is typically colocated with the stream interface inside the corotating interaction region (CIR). If the depression starts ahead of the interface, there is usually an additional abrupt decrease at the interface. In ∼61% of events the onset of the depression is closely associated with the onset of enhanced field turbulence which typically occurs near the stream leading edge. Minimum particle densities are generally found in the vicinity of the maximum solar wind speed in the high‐speed stream. The density recovers during the declining phase of the stream. The observations are most consistent with modulation of the cosmic ray density in high‐speed streams by the increase in solar wind speed. Enhanced scattering by turbulence in the CIR may also contribute near the onset of the depression, in particular in cases where the decrease commences ahead of the stream interface. The absence of a consistent relationship between the depressions and magnetic field enhancements suggests that localized particle drifts in the enhanced magnetic fields of CIRs do not produce the particle depressions. The observation of a depression is not dependent on the presence of a heliospheric current sheet crossing in the CIR, in contrast to previous reports.

Abstract. We have used >60 MeV/amu particle data from Helios 1 and 2 to demonstrate the close association between ejecta (as defined, for example, by regions of depressed solar wind proton temperature) and short-term (<3 days duration) particle decreases. Of 84 short-term decreases of >4%, we find that 88% were associated with an ejecta, and 70% of these were also associated with a shock. It is clear that the presence of a particle decrease is a robust signature for identifying ejecta in the ecliptic, at least within I AU. Conversely, ejecta are evidently important in the production of short-term cosmic ray depressions. The •bsence of • s•mple of well-defined eject• without •n •ssoci•ted p•rticle decrease suggests that extended regions of open field geometry are rare inside ejecta, at least on the --0.005 AU scale sizes probed by these particles. Sixty-three percent of the ejecta decreases were associated with smooth magnetic field rotations characteristic of magnetic clouds. Our results suggest that there is no fundamental difference in the particle response to ejecta with or without magnetic cloud signatures. We find that some ejecta observed at multiple spacecraft have a magnetic cloud signature at one spacecraft but not at another. The most likely explanation is that magnetic clouds are a substructure of ejecta and the field structure observed depends on where the ejecta is intercepted. We also find that ejecta probably typically extend much less in longitude than the 100 ø inferred from single-spacecraft studies.

For a number of impulsive solar particle events we examine variations of maximum intensities and times to maximum intensity as a function of longitude, using observations from the two Helios spacecraft and near the Earth. We find that electrons in the MeV range can be detected more than 80 from the flare longitude, corresponding to a considerably wider ''well connected'' region than that ($20 half-width) reported for 3 He-rich impulsive solar events. This wide range and the decrease of peak intensities with increasing connection angle revive the concept of some diffusive propagation process in the low corona. Delays to intensity maxima are not systematically correlated with connection angles. We argue that interplanetary scattering parallel to the average interplanetary magnetic field, which varies with position in space, plays an important role in flare particle events. In a specific case variations of the time profiles with radial distance and with particle rigidity are used to quantitatively confirm spatial diffusion. For a few cases near the edges of the well-connected region, the very long times to maximum intensity might result from interplanetary lateral transport.

Abstract. Energetic protons in the hundreds of keV to the tens of MeV range frequently are observed in connection with traveling interplanetary shocks. Occasionally, the particle energies ca, n extend up to about 100 MeV. The intensity time profiles at the observer's site are a superposition of the continuous, spatially and temporally variable acceleration at the shock and the subsequent interplanetary propagation. To gain a better understa.nding of both processes a,nd to derive their relevant parameters, we extend a numerical solution of the model of focused transport to accommodate the shock a,s a moving source. No assumptions about the acceleration mecha, nism are ma.de; the shock is treated as a black box. In this paper we introduce the model, discuss its validity, and present model results which have implications for acceleration theory and data interpretation. The main results concerning acceleration and propagation a. re as follows: (1) In the limit of strong scattering and low pa.rticle speeds our model converges toward diffusive shock acceleration. (2) For wea,k scattering or fast particles, spatial diffusion is an insufficient a.pproxima.tion for particle transport; in this case, the physical consequence is a, fast escape from the shock, and the forma.1 consequence is that the standard description of diffusive shock accelera,tion is insufficient. (3) Because of this fast escape, even a. turbulent foreshock region, while it is perfectly capable of keeping 100 keV protons confined to the shock, would allow 10 MeV protons to stream away ea, sily. hnporta.nt results for data interpreta, tion a. re a,s follows'(1) A quasi-exponential intensity increa.se upstrea,m of the shock is not necessarily indicative of diffusive shock acceleration. (2) The intensity at the time of shock passage is a crude measure for the loca,1 a, ccelera. tion efficiency a,s long as it sta.ys constant or continues to rise.