solar energetic particle events: an overview

Solar Energetic Particle Events: An Overview

Christina Cohen

Caltech

Overview of the Overview

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

Space Weather & SEP Events

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)

Space Weather Intensity Spectra Composition Predictions Questions

Space Weather & SEP Events


LASCOLASCOEITMDI

ACEULEIS-SIS

GOES/XRAY


EPAM


EPAM

<4 Rs

LASCO CME time-height profile


Wind/WAVES

Characteristics - IntensityVariability

Varies with everything event time


Characteristics - IntensityVariability

Varies with everything event time species


Oxygen

Protons

Characteristics - IntensityPeak Limitations

streaming limit Reames & Ng 1998 proton-generated

turbulence limits intensities



streaming limit Reames & Ng 1998 proton-generated

turbulence limits intensities

All bets offat ESP events



Exceptions - Jan 20, 2005


Cane et al. 1988

Characteristics - IntensityRise Time

rise time - generally depends on longitude relative to flare Fast=western Slow=eastern




Jan 20, 2005 faster than most W61


>100 MeV



Jan 20, 2005 faster than most W61 >100 MeV fluence

in first few hours was greater than any other event since1976


CME-driven shocks strong shocks - Fermi acceleration


Lee 2005

Characteristics - IntensityTheoretical Understanding

CME-driven shocks strong shocks

• central meridian (nose of shock) gives largest increase


Zank et al. 2001

Characteristics - IntensityTheoretical Understanding

4 of the top 6 events of 1997-2004

Characteristics - SpectraVariability

most large events show roll-off


Oxygen

Characteristics - SpectraVariability

most large events show roll-off

power law events - problem at high energy


Characteristics - SpectraTheoretical Understanding

Power law determined by shock strength Roll-off determined by escape,

species dependent


Li et al. 2005

Lee 2005

Fe

CNO

H

Kinetic energy (MeV/n)

Characteristics - CompositionVariability

mostly protons


H

He

Fe

O

C x 10


mostly protons heavy ions still important

not predictable from proton measurements


H O Fe




very variable





very variable dependent

on energy


Characteristics - CompositionTheoretical Understanding

Shock acceleration Variations depend

on Q/M




on Q/M seed population

(not SW)




on Q/M seed population

(not SW) flare suprathermals

for high Fe events??


Tylka et al. 2005Still don’t know how to generateelement-dependent power law slopes

Current Predictive Capability

Tools neutron monitors L1 monitors (ACE RTSW)

• ESP events• peak events

Solar - CMEs, Flares, Active Regions Theoretical Understanding (models)

But currently can’t predict SEP characteristics from solar observations



Current Techniques shock arrival


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

Vandegriff et al. 2005


Current Techniques shock arrival ESP L1 detection

• 30-60 minutes warning


Current Questions for Study

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 - STEREO, Sentinels


solar energetic particle events: an overview

Documents

studyspace weather

overviewspace weather

longitude relative

radio waves

disposalseps ions

electronsspacecraft

mostw61100 mev fluence

rhessiother mdi