SHINE August 2006
Utah
Interpreting Spectral Forms Observed in
Large Solar Energetic Particle Events
C.M.S. Cohen and R.A. MewaldtCaltech
G.M. MasonAPL
SHINE August 2006
Utah
Observations
• Combined ULEIS + SIS heavy ion spectra• Many large SEP events have breaks in the spectra
• Leads to energy dependent composition
ULEIS SIS
SHINE August 2006
Utah
Observations and Models
• Model of Li et al. also shows – element dependent spectral breaks – energy dependent composition
H
Fe
CNO
SHINE August 2006
Utah
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)Cummings, Stone & Webber
Anomalous Cosmic Rays
SHINE August 2006
Utah
Shifted Spectra• Using oxygen spectra as a ‘template’
• Assume Q/M values Element C N O Ne Mg Si S Ca Fe
Z 6 7 8 10 12 14 16 20 26Q* 5.6 6.6 6.8 8.2 8.9 9.5 10.2 10.8 11.6
*Taken from Klecker et al. [2000] and Möbius et al. [2000]
SHINE August 2006
Utah
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
SHINE August 2006
Utah
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
SHINE August 2006
Utah
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
done previously
SHINE August 2006
Utah
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
done previously
SHINE August 2006
Utah
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
SHINE August 2006
Utah
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
SHINE August 2006
Utah
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
SHINE August 2006
Utah
Ellison-Ramatyfits to spectra for H to Fe from the10/29/03 shock(0600-1200 UT)
The power-law index is fixed at -1.3
The Eo valuesrange from3.5 to 31 MeV/nuc
SHINE August 2006
Utah
Charge-State Measurements from SAMPEX
(Data from Labrador et al.)
Curves: Arnaud and Rothenflug~20 to 60 MeV/nuc
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Utah
Q/M-Dependence of Spectral Breaks at Shocks
Eo (
MeV
/nu
c)
SHINE August 2006
Utah
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.
SHINE August 2006
Utah
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