Interplanetary particles and fields, November 22 to December 6, 1977: Helios, Voyager, and Imp observations between 0.6 and 1.6 AU

In the period November 22 to December 6, 1977, three types of interplanetary flows were observed: a corotating stream, a flare-associated shock wave, and a shock wave driven by ejecta. Helios 2, Imp 7, 8, and Voyager 1, 2 were nearly radially aligned at ≈ 0.6, 1, and 1.6 AU, respectively, while Helios 1 was at ≈0.6 AU and 35° east of Helios 2. The instruments on these spacecraft provided an exceptionally complete description of the particles and fields associated with the three flows and corresponding solar events. Analysis of these data revealed the following results. (1) A corotating stream associated with a coronal hole was observed at 0.6 and 1 AU, but not at 1.6 AU. The stream interface corotated and persisted with little change in structure even though the stream disappeared. A forward shock was observed ahead of the interface and moved from Helios 2 at 0.6 AU to Voyager 1, 2 and 1.6 AU; although the shock was ahead of a corotating stream and interface, the shock was not corotating, because it was not seen at Helios 1, probably because the corotating stream was not stationary. (2) An exceptionally intense type III burst was observed in association with a 2B flare of November 22. The exciter of this burst (a beam of energetic electrons) and plasma oscillations (presumably caused by the electron beam) were observed by Helios 2. (3) A nonspherical shock was observed in association with the November 22 flare. This shock interacted with another shock between 0.6 and 1 AU, and they coalesced to form a single shock that was identified at 1 and at 1.6 AU. (4) A shock driven by ejecta was studied. In the ejecta the density and temperature were unusually low, and the magnetic field intensity was relatively high. This region was preceded by a directional discontinuity at which the magnetic field intensity dropped appreciably. The shock appeared to move globally at a uniform speed, but locally, there were fluctuations in speed and direction of up to 100 km/s and 40°, respectively. (5) Three types of electrostatic waves were observed at the shocks, in different combinations. The detailed wave profiles differed greatly among the shocks, even for spacecraft separations of ≲0.2 AU, indicating a strong dependence on local conditions. However, the same types of fluctuations were observed at 0.6 and at 1.6 AU. (6) Energetic (50–200 keV) protons were accelerated by the shocks. The intensities and durations of the fluxes varied by a factor of 12 over longitudinal distances of ≈ 0.2 AU. The intensities were higher, and the durations were lower, at 1.6 than at 0.6 AU, suggesting a cumulative effect. (7) Energetic (≈ 50 keV) protons from the November 22 flare were observed by all the spacecraft. During the decay, Helios 1 observed no change in intensity when the interface moved past the spacecraft, indicating that particles were injected and moved uniformly on both sides of the interface. Helios 2 observed an increase in flux not seen by Helios 1, reaching maximum at the time that a shock arrived at Helios 2. The intensity dropped abruptly when the interface moved past Helios 2, indicating that the ‘extra’ particles seen by Helios 2 did not penetrate the interface.