# Presentation: 247281

## SEP Acceleration

- C.M.S. Cohen
*Caltech*

## Outline

- Shock acceleration in the IPM
- ESP events
- Observations vs theory
- Observations driving theory
- Flare acceleration
- Impulsive SEP event characteristics
- Shocks in flares?
- Time of Flight studies
- Technique
- Usefulness and questions
- Remaining Questions

## Shocks and ESPs

- Bryant 1962, Explorer 12, 9/30/61
- Associated with Forbush decrease and geomagnetic storm  ‘Energetic Storm Particles’
- Determined that they are ‘locally’ shock accelerated particles (1970s)
- 2 categories:  classic and spike
- 2 acceleration mechanisms
- Nice because can also measure shock parameters

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## ESP and Spike Events

- Spike (LESP)
- Duration of 5-20 minutes
- Arrival within 5-10 minutes of shock
- Rarely exceeds 5 MeV
- Shock drift acceleration at quasi-perpendicular shocks

- ESP
- Duration of several hours
- Arrival maybe ahead or behind shock
- May extend to ~20 MeV
- Diffusive shock acceleration at oblique or quasi-parallel shocks

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## ESP and Spike Events

- Spike (LESP)
- Duration of 5-20 minutes
- Arrival within 5-10 minutes of shock
- Rarely exceeds 5 MeV
- Shock drift acceleration at quasi-perpendicular shocks

- ESP
- Duration of several hours
- Arrival maybe ahead or behind shock
- May extend to ~20 MeV
- Diffusive shock acceleration at oblique or quasi-parallel shocks

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Shock Theory and Observations

- Lee 2005 is currently the definitive work on shock acceleration for gradual SEP events (and ESPs)
- But a paper with 105 equations tends to scare experimenters into using something more simple...

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Shock Theory and Observations

- Late 1970s produced simple 1-D shock theory

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Shock Theory and Observations

- Late 1970s produced simple 1-D shock theory
- Although Lee (1983) cautioned against blindly applying this to all energies, experimenters did anyway...

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Shock Theory and Observations

- Late 1970s produced simple 1-D shock theory
- Although Lee (1983) cautioned against blindly applying this to all energies and all events, experimenters did anyway...
- And found agreement was not so good
- Lee has suggestions as to why (as any good theorist would)

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Shock Theory and Observations

- ESP events are extremely variable

- ESPs   Shock Th.   Impulsive   flare th.   Questions

- Cohen et al. 2005

## Shock Theory and Observations

- ESP events are extremely variable and we aren’t careful about which ones the theory applies to
- Not initially hard spectra
- Not quasi-perpendicular shocks
- Not being transported (rather than accelerated)
- Correct frame of mind
- Need to evaluate the compression ratio in the wave frame not the plasma frame

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Shock Theory and SEP events

- Complications with SEP events
- Effects of escaping the shock region
- Effects of transport (diffusion)
- Evolution of the shock (orientation, strength, etc)

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Diffusion/Trapping Signatures

- Although shock theory predicts this
- We often see this

- Cohen et al. 2002

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Diffusion/Trapping Signatures

- Although shock theory predicts this
- We often see this
- Signature of diffusion
-  = 1/3 v 
- Assume  is a power-law in rigidity
-  ~ (M/Q) E(+1)/2
- Break energies should occur at same value of 

- Cohen et al. 2002

- ESPs   Shock Th.   Impulsive   flare th.   Questions

- Cohen et al. 2002

- E1/E2=[(Q/M)1/(Q/M)2]2/(+1)

## Application to Big SEP Events

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Application to Big SEP Events

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Application to Big SEP Events

- ESPs   Shock Th.   Impulsive   flare th.   Questions

##  values differ for heavies and H, He and vary from event to event
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

- 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

- Application to Big SEP Events

- ESPs   Shock Th.   Impulsive   flare th.   Questions

##  values differ for heavies and H, He and vary from event to event
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
Perhaps proton amplified Alfvén waves 

- 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
- Perhaps proton amplified Alfvén waves

- Application to Big SEP Events

- ESPs   Shock Th.   Impulsive   flare th.   Questions

- k-5/3

## Li et al. have created a numerical model which incorporates 
waves and turbulence
evolution of shock
transport away from shock
heavy ion response
Ion spectra have breaks in them due to escape
Break points should scale as (Q/M)2

- Li et al. have created a numerical model which incorporates
- waves and turbulence
- evolution of shock
- transport away from shock
- heavy ion response
- Ion spectra have breaks in them due to escape
- Break points should scale as (Q/M)2

- Other Shock Models

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## During big October 2003 events SAMPEX measured Q for several elements

- Other Shock Models vs Data

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## During big October 2003 events SAMPEX measured Q for several elements

- Other Shock Models vs Data

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Can shock acceleration explain the observations of Fe-enriched (energy dependent composition)?
Idea of Tylka et al.
seed population isenergy dependent
injection energy is higher for Q-perp

- Idea of Tylka et al.
- seed population isenergy dependent
- injection energy is higher for Q-perp

- Observation Driving Models

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Can shock acceleration explain the observations of Fe-enriched (energy dependent composition)?
Idea of Tylka et al.
seed population isenergy dependent
injection energy is higher for Q-perp

- Idea of Tylka et al.
- seed population isenergy dependent
- injection energy is higher for Q-perp

- Observation Driving Models

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Rough procedure:
Assume spectral shape: Fx(E) ~ E- exp(-E/E0x) 
Incorporate species and Bn dependence through: E0x  ~ [Qx/Ax] [secBn]2/(2-1) 
Average over Bn 
Flare suprathermals are injected at all Bn 
Solar wind suprathermals are weighted by  = cos Bn 
Now vary size of seed components
And you get...

- Assume spectral shape: **F****x****(E) ~ E****-******** exp(-E/E****0x****)**** **
- Incorporate species and Bn dependence through: **E****0x****  ~ [Q****x****/A****x****] [sec********Bn****]****2/(2********-1)**
- Average over Bn
- Flare suprathermals are injected at all Bn
- Solar wind suprathermals are weighted by ****** = cos ********Bn**** **
- Now vary size of seed components
- And you get...

- Observation Driving Models

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Impulsive SEP Events

- Thought to be a result of flare acceleration only
- Characteristics
- 3He/4He enhanced by large factors (x104)
- Enhanced Ne-Si and Fe over CNO as compared to gradual SEP events
- Enhancement of ‘ultra heavy’ ions (Z ≥ 30)
- electron rich
- small intensities and short duration (flares and SEPs)

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Impulsive SEP Events

- ACE can resolve events with much lower 3He/4He ratios than previous missions

- ESPs   Shock Th.   Impulsive   flare th.   Questions

-  keV/n

-  MeV/n

## Impulsive SEP Events

- Composition is understood to be a preferential acceleration dependent on Q/A (rigidity)

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Impulsive SEP Events

- Ultraheavy ions are enhanced greatly (although hard to observe because still very rare)

- ESPs   Shock Th.   Impulsive   flare th.   Questions

*Mason et al., 2004*

## Impulsive SEP Events

- Ultraheavy ions are enhanced greatly (although hard to observe because still very rare)

- ESPs   Shock Th.   Impulsive   flare th.   Questions

*Mason et al., 2004*

## Impulsive SEP Events

- ESPs   Shock Th.   Impulsive   flare th.   Questions

*Mason et al., 2002*

- All similar

- Only 3He
-  broken

- 3He & Fe
- rounded

- Can make spectra of 3He, 4He, and heavy ions
- 3He is often quite different

## Impulsive SEP Events

- Can make spectra of 3He, 4He, and heavy ions
- 3He is often quite different
- But on average ultraheaviesare similar in shape

- ESPs   Shock Th.   Impulsive   flare th.   Questions

*Mason et al., 2002*

## Flare Acceleration Theory

- General model involves resonance between waves and ions which cascades to higher Q/M values
- Fe with lowest Q/M gets enhanced first
- Ne-Si gets enhanced next
- Wave energy may be used up before reaches highest Q/M values
- 3He is done separately through special heating first

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Flare Acceleration Theory

- General model involves resonance between waves and ions which cascades to higher Q/M values
- Fe with lowest Q/M gets enhanced first
- Ne-Si gets enhanced next
- Wave energy may be used up before reaches highest Q/M values
- 3He is done separately through special heating first

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Flare Acceleration Theory

- General model involves resonance between waves and ions which cascades to higher Q/M values
- Fe with lowest Q/M gets enhanced first
- Ne-Si gets enhanced next
- Wave energy may be used up before reaches highest Q/M values
- 3He is done separately through special heating first

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Flare Acceleration Theory

- Can match the data fairly well
- Stochastic model of Petrosian can even reproduce complex 3He and 4He spectra

- ESPs   Shock Th.   Impulsive   flare th.   Questions

- But doesn’t do heavy ions

## Flare Acceleration Theory

- But can cascading waves enhance ultraheavies with their much smaller Q/M?

- ESPs   Shock Th.   Impulsive   flare th.   Questions

- May run out of energy before getting to Fe...
- So far unable to match observations

## Remaining Questions

- What?
- Solar wind is supposed to be seed for gradual SEPs
- Coronal (?) material seed for impulsive SEPs
- Where?
- How low can a shock form in corona and accelerate ions?
- How?
- Flare mechanism is still unclear for all circumstances
- Do quasi-perp shocks have high injection energy?
- Can we tell?
- Maybe by looking at extremes
- Separation at 1 AU may be difficult

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Remaining Questions

- What?
- Solar wind is supposed to be seed for gradual SEPs
- Coronal (?) material seed for impulsive SEPs
- Where?
- How low can a shock form in corona and accelerate ions?
- How?
- Flare mechanism is still unclear for all circumstances
- Do quasi-perp shocks have high injection energy?
- Can we tell?
- Maybe by looking at extremes
- Separation at 1 AU may be difficult

- ESPs   Shock Th.   Impulsive   flare th.   Questions

- How low is Q at suprathermal energies?

## Remaining Questions

- What?
- Solar wind is supposed to be seed for gradual SEPs
- Coronal (?) material seed for impulsive SEPs
- Where?
- How low can a shock form in corona and accelerate ions?
- How?
- Flare mechanism is still unclear for all circumstances
- Do quasi-perp shocks have high injection energy?
- Can we tell?
- Maybe by looking at extremes
- Separation at 1 AU may be difficult

- ESPs   Shock Th.   Impulsive   flare th.   Questions

## Remaining Questions

- What?
- Solar wind is supposed to be seed for gradual SEPs
- Coronal (?) material seed for impulsive SEPs
- Where?
- How low can a shock form in corona and accelerate ions?
- How?
- Flare mechanism is still unclear for all circumstances
- Do quasi-perp shocks have high injection energy?
- Can we tell?
- Maybe by looking at extremes
- Separation at 1 AU may be difficult

- ESPs   Shock Th.   Impulsive   flare th.   Questions