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A Statictical Study of 3He Enhancement in the High-Energy Solar Particles

  • Authors: Laivola, Jarno; Torsti, J.; Kocharov, L.
  • Publication: Proceedings of the 28th International Cosmic Ray Conference. July 31-August 7, 2003. Trukuba, Japan. Under the auspices of the International Union of Pure and Applied Physics p.3233, 2003
  • Solar events from 1999 February 8 to 2000 December 7
  • Statistical study
  • ADS link
  • Abstract: Energetic particle observations of the ERNE instrument (the Energetic and Relativistic Nuclei and Electron experiment) onboard the Solar and Heliospheric Observatory enable the measurements of the 3He flux beyond 15 MeV nucleon‑1 with a good statistical resolution. An overview of the ERNE observations for the period from 8 February 1999 to 7 December 2000 is reported and a comprehensive statistical study is performed to learn regularities of 3He enhancements in the high-energy range of 15-30 MeV nucleon ‑1 . Significant intensities of 3He are detected in all event days with 4He intensity exceeding ≈ 0.5 ion per (m² s sr MeV nucleon‑1 ). The abundance ratio 3He/4He is measured to vary within the range ~ 0.003-2, which is well above the corresponding solar wind value. A histogram of the daily 3He/4He ratio reveals a sharp maximum at 3He/4He ≈ 0.01. Observations and analysis. The early studies of the 3He-rich solar energetic particle (SEP) events are mostly made in low energies, ~ 1 MeV nucleon‑1 , (Ko charov & Ko charov 1984, Reames, Meyer, & von Rosenvinge 1994, and references therein) but some measurements beyond 10 MeV nucleon‑1 has been also carried out (Clayton, Guzik, & Wefel 2000, Bakaldin et al. 2003, Torsti et al. 2002, 2003, and references therein). This survey of SEP events is based on the particle flux measurements by ERNE/HED particle telescope (Torsti et al. 1995) from 8 February 1999 till 7 December 2000. Both helium isotop es, 3He and 4He, were detected in the energy channel 15-30 MeV nucleon‑1 and the average geometric factor for the studied isotop es in this channel is 30.5 cm² sr. During the selected period there were some data gaps lasting from few hours to couple of days when either the spacecraft, or more often, the instrument was not in the observation mode. There were also a couple of strong solar events, like the events in 14 July 2000 and 9 November 2000, producing the extreme particle fluxes exceeding the analysis capacity of ERNE. In those o ccasions, the data have been excluded from the analysis. Figure 1 plots time profiles of 3He and 4He daily count rates during 19992000. The slowly-changing line in the uppermost panel shows a lower limit for.

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