Interpreting Spectral Forms Observed in Large Solar Energetic Particle Events
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Transcript of Interpreting Spectral Forms Observed in Large Solar Energetic Particle Events
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
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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
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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
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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
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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)
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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