A Survey of Bidirectional >= 1 MeV Ion Flows during the HELIOS 1 and HELIOS 2 Missions: Observations from the Goddard Space Flight Center Instruments

Abstract

view Abstract Citations (13) References (44) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Survey of Bidirectional >= 1 MeV Ion Flows during the HELIOS 1 and HELIOS 2 Missions: Observations from the Goddard Space Flight Center Instruments Richardson, I. G. Abstract A survey is made of 1.1-2.1 MeV and 3-21 MeV bidirectional ion flows (BIFs) in the solar wind at 0.3-1.0 AU observed by the Goddard Space Flight Center instruments on the Helios 1 and Helios 2 spacecraft during the spacecraft missions in 1974-1984 and 1976-1980, respectively. Some 774 events have been identified at Helios 1, and 223 at Helios 2, with mean durations of ∼2.5 hr at each spacecraft. BIFs were observed for ∼1%-3% of the observation time during solar minimum conditions in 1975-1977 and for ∼10%-14% in 1980-1981 around solar maximum. These occurrence rates are similar to those of ∼1 MeV BIFs observed at the IMP 8 and ISEE 3 spacecraft, and of bidirectional electron heat fluxes at ISEE 3. Solar wind plasma parameters during BIFs were similar to those found generally during the Helios missions, though BIFs have a greater tendency to be associated with cool, low-β plasma, moderately enhanced and low-variance magnetic fields, and both less than 300 km s-1 and greater than 750 km s-1 solar wind. Solar wind features associated with the greater than 4 hr duration BIFs include clear plasma shock-driver signatures: 36% of the events; postshock plasma, not associated with shock-driver signatures: 13 %; noncompressive density enhancements: ∼22% (half associated with plasma proton temperature depressions); high-speed streams not associated with shocks: ∼10%; corotating interaction regions: ∼5%; immediately upstream of shocks: ∼5%. Around 8% were associated with other solar wind structures, while ∼4% showed no associated structure. BIFs were present in several of the shock drivers associated with coronal mass ejections (CMEs) observed by the Solwind coronagraph during intervals when Helios 1 was off the limbs of the Sun, showing directly the association of some BIFs with CMEs. Publication: The Astrophysical Journal Pub Date: January 1994 DOI: 10.1086/173616 Bibcode: 1994ApJ...420..926R Keywords: SPACE VEHICLES; SUN: PARTICLE EMISSION; SUN: SOLAR WIND full text sources ADS |