Solar activity and heliosphere-wide cosmic-ray modulation in mid-1982
A major episode of flare activity in June and July of 1982 was accompanied by a pair of heliosphere-wide cosmic-ray modulation events. In each case, a large Forbush decrease (FD) at earth was followed in turn by apparently related decreases at Pioneer 11 (P11) and Pioneer 10 (P10). White light coronagraph and near-sun satellite data are reviewed to identify plausible solar origins of these modulation events. The first widespread intensity decrease (FD 1) can be attributed to the combined effects of a backside flare from solar-active region 18382/18383, located 23 in ecliptic longitude from Pioneer 10, and a visible-disk flare from 18405 on June 6, when this region was 9 deg from Pioneer 11. The second widespread modulation event during this period (FD 2) may be linked to flares from active region 18474. Since even fast shocks would take about 1 month to propagate to Pioneer 11 (12 AU) and about 2 months to reach Pioneer 10 (28 AU) in mid-1982, these one-to-one associations must be regarded with caution. The processes of entrainment and coalescence can cause a given traveling interplanetary disturbance to lose its identity enroute to the outer heliosphere. The ability to identify plausible solar-flare candidates for each of the four Forbush-like decreases observed at the Pioneer satellites removes the need to invoke a shock from a single flare as the sole cause of either FD 1 (at both P10 and P11) or FD 2.
- Research Organization:
- Air Force Geophysics Lab., Hanscom AFB, MA (USA)
- OSTI ID:
- 5312251
- Report Number(s):
- AD-A-188433/7/XAB; AFGL-TR-87-0294
- Resource Relation:
- Other Information: Pub. in Jnl. of Geophysical Research, Vol. 92, No. A8, 8487-8501(1 Aug 1987)
- Country of Publication:
- United States
- Language:
- English
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