Solar flare protons and alpha particles during the last three solar cycles
Event-integrated fluxes of protons and alpha particles in solar-flare-associated particle events during solar cycle 21 (1976--1986) are determined from data obtained by detectors on board the IMP-7 and IMP-8 satellites. Sixty-three solar particle events with proton fluence (E>10 MeV)>10/sup 7/ cm/sup -2/ were identified from October 1972 to March 1987. The average omnidirectional flux of protons with kinetic energy>10 MeV for cycle 21, 64 cm/sup -2/ s/sup -1/, is lower than the corresponding number for cycle 20 (92 cm/sup -2/ s/sup -1/) based on satellite data and for the cycle 19 (378 cm/sup -2/ s/sup -1/) based on lunar sample data. Six large events contributed 70% of the total proton fluence during solar cycle 21. Several events in early 1981 with high proton fluences could account for much of the high /sup 56/Co radioactivities observed in the small-sized Salem meteorite. The event-averaged alpha-particle to proton ratio in the energy interval 1--10 MeV/nucleon varies from 0.006 to 0.05, with an average value of 0.02 for the whole cycle. The events during solar cycle 21 are characterized by softer spectra for both protons and alpha particles compared to those in earlier solar cycles. No definitive correlation exists between cycle-averaged solar flare proton fluxes and peak sunspot numbers. A comparison with long-term (million year) averaged data for these parameters, obtained from lunar sample data, shows that the contemporary solar flare proton spectra are characterized by softer spectra (lower R/sub 0/ values). A similar comparison cannot be made for the mean long-term averaged flux, as the contemporary average suffers from uncertainty due to statistics of single events.
- Research Organization:
- Physical Research Laboratory, Ahmedabad, India
- OSTI ID:
- 6952917
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 93:A7
- Country of Publication:
- United States
- Language:
- English
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GENERAL PHYSICS
SOLAR ALPHA PARTICLES
RADIATION FLUX
SOLAR FLARES
SOLAR PROTONS
IMP SATELLITES
METEORITES
MEV RANGE
PROTON DENSITY
SOLAR CYCLE
SUNSPOTS
ALPHA PARTICLES
BARYONS
CHARGED PARTICLES
ELEMENTARY PARTICLES
ENERGY RANGE
FERMIONS
HADRONS
NUCLEONS
PROTONS
RADIATIONS
SATELLITES
SOLAR ACTIVITY
SOLAR PARTICLES
SOLAR RADIATION
STARSPOTS
STELLAR ACTIVITY
STELLAR RADIATION
640104* - Astrophysics & Cosmology- Solar Phenomena