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Solar Energetic Particle Events: An Overview

Solar Energetic Particle Events: An Overview. Christina Cohen Caltech. Overview of the Overview. Space Weather and SEP events Why? Tools we can use Characteristics of interest Intensity (peak, rise time, duration) Spectra Composition Current predictive capability

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Solar Energetic Particle Events: An Overview

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  1. Solar Energetic Particle Events: An Overview Christina Cohen Caltech

  2. Overview of the Overview • Space Weather and SEP events • Why? • Tools we can use • Characteristics of interest • Intensity (peak, rise time, duration) • Spectra • Composition • Current predictive capability • Current questions for study

  3. Space Weather Intensity Spectra Composition Predictions Questions Space Weather & SEP Events • Why? • Danger to astronauts, instruments, power grids, etc • Understanding enables predictions • Tools at our disposal • SEPs (ions, electrons) • Spacecraft (ACE, Wind, SoHO, GOES) • Neutron monitors • Solar • CMEs (LASCO) • X-ray (SXI, GOES, RHESSI) • Other (MDI, EIT, TRACE...) • Radio (WAVES, ground-based)

  4. Space Weather Intensity Spectra Composition Predictions Questions Space Weather & SEP Events MDI EIT LASCO LASCO GOES/XRAY ACE ULEIS-SIS

  5. Space Weather Intensity Spectra Composition Predictions Questions EPAM

  6. Space Weather Intensity Spectra Composition Predictions Questions EPAM LASCO CME time-height profile <4 Rs

  7. Space Weather Intensity Spectra Composition Predictions Questions Wind/WAVES

  8. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - IntensityVariability • Varies with everything • event • time

  9. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - IntensityVariability Oxygen • Varies with everything • event • time • species Protons

  10. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - IntensityPeak Limitations • streaming limit Reames & Ng 1998 • proton-generated turbulence limits intensities

  11. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - IntensityPeak Limitations • streaming limit Reames & Ng 1998 • proton-generated turbulence limits intensities • All bets offat ESP events

  12. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - IntensityPeak Limitations • Exceptions - Jan 20, 2005

  13. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - IntensityRise Time • rise time - generally depends on longitude relative to flare • Fast=western • Slow=eastern Cane et al. 1988

  14. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - IntensityRise Time • rise time - generally depends on longitude relative to flare • Fast=western • Slow=eastern • Jan 20, 2005 • faster than most • W61 >100 MeV

  15. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - IntensityRise Time • rise time - generally depends on longitude relative to flare • Fast=western • Slow=eastern • Jan 20, 2005 • faster than most • W61 • >100 MeV fluencein first few hours was greater than any other event since1976

  16. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - IntensityTheoretical Understanding • CME-driven shocks • strong shocks - Fermi acceleration Lee 2005

  17. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - IntensityTheoretical Understanding Zank et al. 2001 • CME-driven shocks • strong shocks • central meridian (nose of shock) gives largest increase 4 of the top 6 events of 1997-2004

  18. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - SpectraVariability • most large events show roll-off Oxygen

  19. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - SpectraVariability • most large events show roll-off • power law events - problem at high energy

  20. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - SpectraVariability • most large events show roll-off • power law events - problem at high energy

  21. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - SpectraTheoretical Understanding • Power law determined by shock strength • Roll-off determined by escape,species dependent Li et al. 2005 CNO Lee 2005 H Fe Kinetic energy (MeV/n)

  22. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - CompositionVariability • mostly protons H He C x 10 O Fe

  23. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - CompositionVariability • mostly protons • heavy ions still important • not predictable from proton measurements H O Fe

  24. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - CompositionVariability • mostly protons • heavy ions still important • not predictable from proton measurements • very variable

  25. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - CompositionVariability • mostly protons • heavy ions still important • not predictable from proton measurements • very variable • dependent on energy

  26. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - CompositionTheoretical Understanding • Shock acceleration • Variations dependon Q/M

  27. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - CompositionTheoretical Understanding • Shock acceleration • Variations dependon Q/M • seed population (not SW)

  28. Space Weather Intensity Spectra Composition Predictions Questions Characteristics - CompositionTheoretical Understanding • Shock acceleration • Variations dependon Q/M • seed population (not SW) • flare suprathermals for high Fe events?? Still don’t know how to generate element-dependent power law slopes Tylka et al. 2005

  29. Space Weather Intensity Spectra Composition Predictions Questions Current Predictive Capability • Tools • neutron monitors • L1 monitors (ACE RTSW) • ESP events • peak events • Solar - CMEs, Flares, Active Regions • Theoretical Understanding (models) • But currently can’t predict SEP characteristics from solar observations

  30. Space Weather Intensity Spectra Composition Predictions Questions Current Predictive Capability • Current Techniques • shock arrival • Average uncertainty in arrival time • 24 hrs in advance => 8.9 hrs • 12 hrs in advance => 4.6 hrs Vandegriff et al. 2005

  31. Space Weather Intensity Spectra Composition Predictions Questions Current Predictive Capability • Current Techniques • shock arrival • ESP L1 detection • 30-60 minutes warning

  32. Space Weather Intensity Spectra Composition Predictions Questions Current Questions for Study • Acceleration • Details of the process • Requirements • Pre-conditioning • Turbulence from previous events • Suprathermal population (flares) • Solar signatures • What feature? CME brightness/speed? Flare size/duration? • future missions - STEREO, Sentinels

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