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

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

Jan 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...420..926r&link_type=abstract

Astrophysical Journal v.420, p.926

Astronomy and Astrophysics

Astronomy

8

Space Vehicles, Sun: Particle Emission, Sun: Solar Wind

Scientific paper

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.

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