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Heavy Ion Abundances in Large Solar Energetic Particle Events Spring AGU 2006, SH43B-04

Heavy Ion Abundances in Large Solar Energetic Particle Events Spring AGU 2006, SH43B-04. Mihir I. Desai Southwest Research Institute San Antonio, Texas Co-authors: G. M. Mason, R. E. Gold, S. M. Krimigis, C. M. S. Cohen, R. A. Mewaldt, J. E. Mazur & J. R. Dwyer.

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Heavy Ion Abundances in Large Solar Energetic Particle Events Spring AGU 2006, SH43B-04

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  1. Heavy Ion Abundances in Large Solar Energetic Particle Events Spring AGU 2006, SH43B-04 Mihir I. Desai Southwest Research Institute San Antonio, Texas Co-authors: G. M. Mason, R. E. Gold, S. M. Krimigis, C. M. S. Cohen, R. A. Mewaldt, J. E. Mazur & J. R. Dwyer

  2. Event Selection & Data Analysis • 85 solar proton events that affected the Earth environment between Nov. 1997 - Jan. 2005 (source: NOAA SPE event list; criteria: 10 PFU’s for >10 MeV protons) • Removed 21 events where: • ULEIS intensities were dominated by IP shock-accelerated ions • ULEIS was completely saturated • Little or no intensity increases at ~1 MeV/n. and/or at ~100 keV/n. • Events with complex time-histories with multiple CMEs, flares, and IP shock contributions

  3. Nov. 24, 2001 SEP Sampling Interval with shock passage masked STEP 1Start time - Flare/CME onsetStop Time - End of SEP decaySTEP 2Mask ESP intervalsSTEP 3Select energy-dependent start intervals using smoosh plots.

  4. 29 of the 64 events have finite 3He Enhancements ~4-150 times SW value August 20, 2002 Correlation is not statistically significant 3He/4He = 11.96 +/-0.99 (x10-3) 0.5-2.0 MeV/n

  5. 486 CME shocks Must encounter 3He- and heavy ion-rich flare material in the corona and the IP medium

  6. Energy-dependent Fe/O in large SEP events • Fe/O decreases with increasing energy - due to shock acceleration • Fe/O is enhanced relative to SW value (unknown mechanism) Fe/O Depleted Fe/O Enhanced

  7. LSEP abundances vs. Slow Solar wind Not well organized by any simple physical quantity (e.g., M/Q ratio, FIP, etc.) ACE/ULEIS 0.32-0.45 MeV/n Ulysses/SWICS solar wind

  8. This survey vs. SEP events Enhanced relative to gradual SEPs at ~5-12 MeV/n Depleted relative to 3He-rich events ACE/ULEIS 0.32-0.45 MeV/n

  9. M/Q-dependent event-to-event variations LSEP events ACE/ULEIS 0.32-0.45 MeV/n

  10. M/Q-dependent event-to-event variations in IP shocks + LSEP events ACE/ULEIS 0.32-0.45 MeV/n

  11. M/Q-dependent variations - IP shocks, LSEP events , 3He-rich SEP events ACE/ULEIS 0.32-0.45 MeV/n

  12. Same fit works for LSEP events, 3He-rich events, and IP shocks ACE/ULEIS 0.32-0.45 MeV/n

  13. Two distinct M/Q-dependent mechanisms • Fe/O decreases with increasing energy - due to shock acceleration • Fe/O is enhanced relative to SW value - due to the seed population • Fe/O in the seed population must be larger than LSEPs Fe/O Depleted Fe/O Enhanced

  14. M/Q-dependent depletion relative to “seed” population IP shock vs. ambient Apply this function to infer source abundances from measured LSEP values Desai et al., 2004

  15. Inferred Source Abundances Comprises ~75% impulsive SEP-like material

  16. Summary • Fe/O decreases with energy up to ~60 MeV/n - signature of shock acceleration • 3He and heavy ions show large, variable, and unsystematic enhancements relative to SW values - Heavy ion abundances are not organized by a simple quantity wrt. SW values • Same M/Q-dependent enhancements are seen in IP shocks, LSEP events, and 3He-rich events

  17. Conclusion The event-to-event variability in the ion composition in large SEP events at ULEIS energies can be attributed primarily to that of suprathermal seed population, most of which originates from processes similar to those occurring during 3He-rich SEP events.

  18. Large SEP events at ACE 64 large SEP events (NOAA’s SPE list) between 1997-Jan 2005

  19. Aug. 24, 2002

  20. Energy-dependence of C/O and Fe/O C/O ratios remain constant with energy;Fe/O decreases by a factor of 2

  21. Same situation For 9 events with Fe/O <0.1 and upper limit 3He/4He

  22. Comparison with prior surveys Fe/O at ULEIS energies are greater than prior surveys at higher energies

  23. Solar activity Fe/O exhibits no clear solar cycle dependence50% of events have finite 3He during 1998-2003 Occ. freq. drops below ~25% in 2004

  24. Fe/O ratio is poorly correlated with CME speed & flare longitude

  25. Event-integrated Fe/O vs.Mean Fe/O from 1 hr. averages

  26. Fe/O LSEPs vs. Pre-event Unlike for IP shocks, the Fe/O in LSEPs is not correlated with pre-event Fe/O on a case-by-case basis

  27. Perhaps STEREO will help sample the seed population for some LSEP events

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