Interpreting Spectral Forms Observed in Large Solar Energetic Particle Events

1. Interpreting Spectral Forms Observed in Large Solar Energetic Particle Events C.M.S. Cohen and R.A. Mewaldt Caltech G.M. Mason APL Utah

2. ULEIS SIS Observations • Combined ULEIS + SIS heavy ion spectra • Many large SEP events have breaks in the spectra • Leads to energy dependent composition Utah

3. H CNO Fe Observations and Models • Model of Li et al. also shows • element dependent spectral breaks • energy dependent composition Utah

4. Anomalous Cosmic Rays Cummings, Stone & Webber Diffusion Effects • Motivated by observations of ACRs, examine diffusion coefficients  = 1/3 v  • Assume  is a power-law in rigidity  ~ (M/Q) E(+1)/2 • Break energies should occur at same value of  E1/E2=[(Q/M)1/(Q/M)2]2/(+1) Utah

5. Shifted Spectra • Using oxygen spectra as a ‘template’ • Assume Q/M values Utah

6. Shifted Spectra • Using oxygen spectra as a ‘template’ • Assume Q/M values • Use E-break scaling law E1/E2=[(Q/M)1/(Q/M)2]2/(+1) and determine best  value for each SEP event to obtain energy-independent composition • Produces one  value per event October-November 2003 events Cohen et al. 2005 Utah

7. Current Results • Two events (2001 Dec 26, 2002 Feb 20) did not have sufficient breaks to constrain the analysis • Results reasonably similar in quality to previous analysis • highest and lowest energies do not always track • Ca is often different 2001 Nov 4 2001 Dec 26 2002 Feb 20 2002 Apr 21 2002 Aug 24 2002 Nov 9 Utah

8. done previously Current Results • Alpha values are slightly lower than previous analysis (0.6-1.3 vs 0.8-2.7) • Correlated with Fe/O at 0.5 MeV/n?? • probably not if remove two ‘unconstrained’ points • two points at same  have different Fe/O Utah

9. done previously Current Results • Alpha values are slightly lower than previous analysis (0.6-1.3 vs 0.8-2.7) • Not correlated with Fe/O at 10 MeV/n Utah

10. Relation to Wave Spectra • Values of  can be related to turbulence spectrum ~k-q  = 2-q (Droege, 1994) • Wave indices < 5/3 suggest there is an additional source of turbulence present Utah

11. Relation to Wave Spectra • Ng, Reames and Tylka (2003) showed that proton-amplified Alfven waves can substantially distort the wave spectrum • The distortion is in the general rigidity (energy) region of the spectral breaks • Distortion can result in regions of flat or increasing wave spectra Utah

12. At the Shock • Spectra just downstream of the shock can be examined for spectral breaks • This is where the forms from Ellison and Ramaty are most applicable • We also have some measured charge state values at high energies from MAST/SAMPEX during the events with big shocks (10/28/2003 and 10/29/2003) • Simulations of Li et al. suggest break points will be organized as (Q/M)2 Utah

13. Ellison-Ramaty fits to spectra for H to Fe from the 10/29/03 shock (0600-1200 UT) The power-law index is fixed at -1.3 The Eo values range from 3.5 to 31 MeV/nuc Utah

14. Charge-State Measurements from SAMPEX (Data from Labrador et al.) Curves: Arnaud and Rothenflug ~20 to 60 MeV/nuc Utah

15. Q/M-Dependence of Spectral Breaks at Shocks Eo (MeV/nuc) Utah

16. Summary • Large SEP events often have spectral breaks which leads to energy-dependent composition • Some of this can be understood through diffusion effects away from the acceleration region • although the Qs are assumed and not measured/varied • Many events indicate a source of additional turbulence near the acceleration region • Examination of 2 ESP events shows Q/M organization of the spectral breaks • 1 agrees with Li et al. prediction of (Q/M)2 • 1 does not agree with Li et al. Utah

17. Future Work • Examine other • events • ESP intervals • elements (H, He, C, N) • Explore the effect of different charge state assumptions • Investigate correlations between  and • shock parameters • CME parameters Utah