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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, A10101, doi:10.1029/2003JA010194, 2004

Solar cycle variations in solar and interplanetary ions observed with Interplanetary Monitoring Platform 8

K. D. C. Simunac

Fundamental Technologies LLC, Lawrence, Kansas, USA


T. P. Armstrong

Fundamental Technologies LLC, Lawrence, Kansas, USA


Abstract

Energetic protons (0.39–440 MeV), alpha particles (0.59–52 MeV/nucleon), and medium nuclei (carbon, nitrogen, and oxygen; 0.7–8.8 MeV/nucleon) have been observed with the Charged Particle Measurement Experiment (CPME) aboard the Interplanetary Monitoring Platform 8 (IMP 8) spacecraft from 1973 to the present. We summarize the results obtained for the period October 1973 through November 2000, more than two complete solar cycles. We believe that these observations of solar and interplanetary particles are the longest set from a single instrument yet obtained. Artifacts have been carefully removed from this data set, including background changes due to the failure in 1989 of an electronic anticoincidence shield. We have computed averages over individual solar cycles as well as “grand” averages of everything seen over the 27-year period. The “grand” average energy spectrum of protons, alphas, and medium nuclei is well described by a power law function in total energy with exponent −2, where E is in units of MeV total energy and flux is particles/(cm2 s sr MeV). Compositional abundance ratios for energetic nuclei at the same speeds are calculated for times of minimum (H/He = 30; He/medium = 95) and maximum (H/He = 61; He/medium = 45) solar activity. We also considered possible relationships between sunspot number and interplanetary particle flux using a variety of averaging intervals and time lags and leads but found no result that could be used to predict particle fluxes from sunspot numbers over short intervals (typically several solar rotations).

Received 15 August 2003; accepted 11 May 2004; published 1 October 2004.

Keywords: solar cycle; interplanetary particle flux; energy spectra; proton fluence; energetic particles.

Index Terms: 2118 Interplanetary Physics: Energetic particles, solar; 2162 Interplanetary Physics: Solar cycle variations (7536); 2114 Interplanetary Physics: Energetic particles, heliospheric (7514); 2139 Interplanetary Physics: Interplanetary shocks.

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Citation: Simunac, K. D. C., and T. P. Armstrong (2004), Solar cycle variations in solar and interplanetary ions observed with Interplanetary Monitoring Platform 8, J. Geophys. Res., 109, A10101, doi:10.1029/2003JA010194.