Solar Energetic Particle Events: An Overview

1
Solar Energetic Particle Events An Overview

• Christina Cohen
• Caltech

2
Overview of the Overview

• What are SEP events?
• Space Weather and SEP events
• Why?
• Tools we can use
• Characteristics of interest
• Intensity (peak, rise time, duration)
• Spectra
• Composition
• Current predictive capability
• Current questions for study

3
SEP Events
Space Weather Intensity Spectra
Composition Predictions Questions

• What are they?
• Ions Electrons

4
SEP Events
Space Weather Intensity Spectra
Composition Predictions Questions

• What are they?
• Ions Electrons
• Large ones are accelerated by CME-driven shocks

5
SEP Events
Space Weather Intensity Spectra
Composition Predictions Questions
dE/dx ? (Z/V)2 ? (MZ2/E) E dE/dx ? Z2M dE/dx
?E/ L ?E/(L0 sec ?)

• What are they?
• Ions Electrons
• Large ones are accelerated by CME-driven shocks
• How do we measure them?
• Spacecraft based instrumentation (GOES, Wind,
  ACE, SoHO, STEREO)
• dE/dx vs E time of flight

6
Space Weather SEP Events
Space Weather Intensity Spectra
Composition Predictions Questions

• Why?
• Danger to astronauts, instruments, power grids,
  etc
• Understanding enables predictions
• Tools at our disposal
• SEPs (ions, electrons)
• Spacecraft (ACE, Wind, SoHO, GOES)
• Neutron monitors
• Solar
• CMEs (LASCO)
• X-ray (SXI, GOES, RHESSI)
• Other (MDI, EIT, TRACE...)
• Radio (WAVES, ground-based)

7
Space Weather SEP Events
Space Weather Intensity Spectra
Composition Predictions Questions
LASCO
LASCO
EIT
MDI
GOES/XRAY
ACE ULEIS-SIS
8
Space Weather Intensity Spectra
Composition Predictions Questions
EPAM
9
Space Weather Intensity Spectra
Composition Predictions Questions
EPAM
LASCO CME time-height profile
lt4 Rs
10
Space Weather Intensity Spectra
Composition Predictions Questions
Wind/WAVES
11
Characteristics - IntensityVariability
Space Weather Intensity Spectra
Composition Predictions Questions

• Varies with everything
• event
• time

12
Characteristics - IntensityVariability
Space Weather Intensity Spectra
Composition Predictions Questions
Oxygen

• Varies with everything
• event
• time
• species

Protons
13
Characteristics - IntensityPeak Limitations
Space Weather Intensity Spectra
Composition Predictions Questions

• streaming limit Reames Ng 1998
• proton-generated turbulence limits intensities

14
Characteristics - IntensityPeak Limitations
Space Weather Intensity Spectra
Composition Predictions Questions

• streaming limit Reames Ng 1998
• proton-generated turbulence limits intensities
• All bets offat ESP events

15
Characteristics - IntensityPeak Limitations
Space Weather Intensity Spectra
Composition Predictions Questions

• Exceptions - Jan 20, 2005

16
Characteristics - IntensityRise Time
Space Weather Intensity Spectra
Composition Predictions Questions

• rise time - generally depends on longitude
  relative to flare
• Fastwestern
• Sloweastern

Cane et al. 1988
17
Characteristics - IntensityRise Time
Space Weather Intensity Spectra
Composition Predictions Questions

• rise time - generally depends on longitude
  relative to flare
• Fastwestern
• Sloweastern
• Jan 20, 2005
• faster than most
• W61

gt100 MeV
18
Characteristics - IntensityRise Time
Space Weather Intensity Spectra
Composition Predictions Questions

• rise time - generally depends on longitude
  relative to flare
• Fastwestern
• Sloweastern
• Jan 20, 2005
• faster than most
• W61
• gt100 MeV fluencein first few hours was greater
  than any other event since1976

19
Characteristics - IntensityTheoretical
Understanding
Space Weather Intensity Spectra
Composition Predictions Questions

• CME-driven shocks
• strong shocks - Fermi acceleration

Lee 2005
20
Characteristics - IntensityTheoretical
Understanding
Space Weather Intensity Spectra
Composition Predictions Questions
Zank et al. 2001

• CME-driven shocks
• strong shocks
• central meridian (nose of shock) gives largest
  increase

4 of the top 6 events of 1997-2004
21
Characteristics - SpectraVariability
Space Weather Intensity Spectra
Composition Predictions Questions

• most large events show roll-off

Oxygen
22
Characteristics - SpectraVariability
Space Weather Intensity Spectra
Composition Predictions Questions

• most large events show roll-off
• power law events - problem at high energy

23
Characteristics - SpectraVariability
Space Weather Intensity Spectra
Composition Predictions Questions

• most large events show roll-off
• power law events - problem at high energy

24
Characteristics - SpectraTheoretical
Understanding
Space Weather Intensity Spectra
Composition Predictions Questions

• Power law determined by shock strength
• Roll-off determined by escape,species dependent

Li et al. 2005
CNO
Lee 2005
H
Fe
Kinetic energy (MeV/n)
25
Characteristics - CompositionVariability
Space Weather Intensity Spectra
Composition Predictions Questions

• mostly protons

H
He
C x 10
O
Fe
26
Characteristics - CompositionVariability
Space Weather Intensity Spectra
Composition Predictions Questions

• mostly protons
• heavy ions still important
• not predictable from proton measurements

H
O
Fe
27
Characteristics - CompositionVariability
Space Weather Intensity Spectra
Composition Predictions Questions

• mostly protons
• heavy ions still important
• not predictable from proton measurements
• very variable

28
Characteristics - CompositionVariability
Space Weather Intensity Spectra
Composition Predictions Questions

• mostly protons
• heavy ions still important
• not predictable from proton measurements
• very variable
• dependent on energy

29
Characteristics - CompositionTheoretical
Understanding
Space Weather Intensity Spectra
Composition Predictions Questions

• Shock acceleration
• Variations dependon Q/M

30
Characteristics - CompositionTheoretical
Understanding
Space Weather Intensity Spectra
Composition Predictions Questions

• Shock acceleration
• Variations dependon Q/M
• seed population (not SW)

31
Characteristics - CompositionTheoretical
Understanding
Space Weather Intensity Spectra
Composition Predictions Questions

• Shock acceleration
• Variations dependon Q/M
• seed population (not SW)
• flare suprathermals for high Fe events??

Still dont know how to generate element-dependent
power law slopes
Tylka et al. 2005
32
Current Predictive Capability
Space Weather Intensity Spectra
Composition Predictions Questions

• Tools
• neutron monitors
• L1 monitors (ACE RTSW)
• ESP events
• peak events
• Solar - CMEs, Flares, Active Regions
• Theoretical Understanding (models)
• But currently cant predict SEP characteristics
  from solar observations

33
Current Predictive Capability
Space Weather Intensity Spectra
Composition Predictions Questions

• Current Techniques
• shock arrival

• Average uncertainty in arrival time
• 24 hrs in advance gt 8.9 hrs
• 12 hrs in advance gt 4.6 hrs

Vandegriff et al. 2005
34
Current Predictive Capability
Space Weather Intensity Spectra
Composition Predictions Questions

• Current Techniques
• shock arrival
• ESP L1 detection
• 30-60 minutes warning

35
Current Predictive Capability
Space Weather Intensity Spectra
Composition Predictions Questions

• Current Techniques
• shock arrival
• ESP L1 detection
• 30-60 minutes warning
• Electrons
• 60 minutes warning

36
(No Transcript)
37
Current Predictive Capability
Space Weather Intensity Spectra
Composition Predictions Questions

• Current Techniques
• shock arrival
• ESP L1 detection
• 30-60 minutes warning
• Electrons
• 60 minutes warning
• Fluence limits from suprathermals

38
Current Questions for Study
Space Weather Intensity Spectra
Composition Predictions Questions

• Acceleration
• Details of the process
• Requirements
• Pre-conditioning
• Turbulence from previous events
• Suprathermal population (flares)
• Solar signatures
• What feature? CME brightness/speed? Flare
  size/duration?
• future missions Solar Probe, Sentinels

39
Current Questions for Study
Space Weather Intensity Spectra
Composition Predictions Questions
STEREO Launch
ACE H gt 10 MeV

• Acceleration
• Details of the process
• Requirements
• Pre-conditioning
• Turbulence from previous events
• Suprathermal population (flares)
• Solar signatures
• What feature? CME brightness/speed? Flare
  size/duration?
• future missions Solar Probe, Sentinels

STEREO Now
STEREO Launch