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

SHINE August 2006

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