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Maher Al Dayeh , J. Dwyer, H. Rassoul

Elemental abundance variations of Solar Energetic Particles at low energies as measured by WIND/ STEP over the last solar cycle. Maher Al Dayeh , J. Dwyer, H. Rassoul Dept. of Physics & Space Sciences, Florida Institute of Technology, Melbourne, FL G. M. Mason and M. I. Desai

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Maher Al Dayeh , J. Dwyer, H. Rassoul

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  1. Elemental abundance variations of Solar Energetic Particles at low energies as measured by WIND/ STEP over the last solar cycle Maher Al Dayeh, J. Dwyer, H. Rassoul Dept. of Physics & Space Sciences, Florida Institute of Technology, Melbourne, FL G. M. Mason and M. I. Desai Department of Physics, University of Maryland, College Park, MD J. E. Mazur The Aerospace Corporation, El Segundo, CA

  2. Solar Energetic Particle (SEP) Events Fe: 0.02 MeV/nuc < 0.15 MeV/nuc CNO: 0.02 MeV/nuc < 0.15 MeV/nuc 0.02MeV/nuc < 0.15 MeV/nuc0.02 MeV/nuc < 0.15 MeV/nuc • Impulsive • Gradual

  3. Particle Instrumentation capabilities: • Extended energy spectra, Isotopic Composition, Ionic Charge States. • Simultaneous Observations of particles, CMEs, solar wind, radio emissions, and solar flares • Interesting problems: • Seed populations of SEPs • Acceleration and Propagation Mechanisms • Spectral and Compositional behaviors. • Elemental Variability within the same classes of events.

  4. Elemental Abundance Variability • Solar Cycle dependence • Variations at low energies: Suprathermal material acceleration . • Heliospheric Shock acceleration mechanisms • Solar lift-off location dependence. • A wider view of impulsive Vs Gradual behaviors.

  5. Data Set • Survery of 94 Gradual events • 47 “good events” • Selection Criteria: • Temporal intensity profile • Velocity dispersion Excluded: Shocks, upstream events, and saturation times

  6. Instrumentation Supra Thermal Energetic Particle Telescope (STEP): Launched onboard WIND on November 1, 1994 Time of Flight Mass Spectrometer Measured species: Protons to Fe Energy range: ~30 keV to ~2 MeV/nuc Instrument geometrical factor: 2 x 0.4 cm2 sr

  7. Extracting Carbon

  8. Intensity Variations

  9. Conclusions Analysis shows that for gradual SEP events, the dependence of the C/O ratio (0.04 MeV/nuc < E < 0.5 MeV/nuc) abundance variation on the solar cycle is not clear due to the large individual event-to-event fluctuations exceeding a factor of two in some cases. However, the overall average is lower than the coronal values inferred from high energy measurements. Low energy (<325 keV) Fe/CNO and NeS/CNO Abundance variation do not show cycle dependence. However, He/CNO shows an interesting feature at the peak of the solar maximum, more investigation need to be done.

  10. Future work We will identify source locations for the events and compare elemental abundance variability with source characteristics of the events (e.g. in coronal holes).  We will expand the energy range of the C/O up to few MeVs using ULEIS/ACE to see how it changes with the energy. Using ULEIS, we will look for solar cycle variations in the SEP integrated fluxes at wider energy ranges. We will expand our study to cover more elements and the recent time periods.

  11. Thank you MAD 2005

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