Heavy Ion Abundances in Large Solar Energetic Particle Events

Spring AGU 2006, SH43B-04

Mihir I. DesaiSouthwest Research Institute

San Antonio, Texas

Co-authors: G. M. Mason, R. E. Gold, S. M. Krimigis, C. M. S.

Cohen, R. A. Mewaldt, J. E. Mazur & J. R. Dwyer

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Event Selection & Data Analysis

• 85 solar proton events that affected the Earth environment between Nov. 1997 - Jan. 2005 (source: NOAA SPE event list; criteria: 10 PFU’s for >10 MeV protons)

• Removed 21 events where:• ULEIS intensities were dominated by IP shock-

accelerated ions• ULEIS was completely saturated • Little or no intensity increases at ~1 MeV/n. and/or

at ~100 keV/n.• Events with complex time-histories with multiple

CMEs, flares, and IP shock contributions

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Nov. 24, 2001

SEP Sampling Interval with shock passage masked

STEP 1Start time - Flare/CME onsetStop Time - End of SEP decay

STEP 2Mask ESP intervals

STEP 3Select energy-dependent start intervals using smoosh plots.

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

29 of the 64 events have finite 3He

Enhancements Enhancements ~4-150 times ~4-150 times SW valueSW value

August 20, 2002

0.5-2.0 MeV/n

3He/4He = 11.96 +/-0.99 (x10-3)

Correlation is not statistically significant

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Must encounter Must encounter 3He- and heavy 3He- and heavy ion-rich flare ion-rich flare material in the material in the corona and the corona and the IP mediumIP medium

486CME shocks

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Fe/O decreases with increasing energy - due to shock acceleration

Fe/O is enhanced relative to SW value (unknown mechanism)

Energy-dependent Fe/O in large SEP events

Fe/O Enhanced

Fe/O Depleted

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

LSEP abundances vs. Slow Solar wind

Not well organized by any simple physical quantity (e.g., M/Q ratio, FIP, etc.)

ACE/ULEIS 0.32-0.45 MeV/n

Ulysses/SWICS solar wind

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

This survey vs. SEP events Enhanced

relative to gradual SEPs at ~5-12 MeV/n

Depleted relative to 3He-rich events

ACE/ULEIS 0.32-0.45 MeV/n

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

M/Q-dependent event-to-event variations LSEP

eventsACE/ULEIS 0.32-0.45 MeV/n

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

ACE/ULEIS 0.32-0.45 MeV/n

M/Q-dependent event-to-event variations in IP shocks + LSEP events

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

ACE/ULEIS 0.32-0.45 MeV/n

M/Q-dependent variations - IP shocks, LSEP events , 3He-rich

SEP events

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Same fit works for LSEP events, 3He-rich events, and IP shocks

ACE/ULEIS 0.32-0.45 MeV/n

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Fe/O decreases with increasing energy - due to shock acceleration

Fe/O is enhanced relative to SW value - due to the seed population

Fe/O in the seed population must be larger than LSEPs

Two distinct M/Q-dependent mechanisms

Fe/O EnhancedFe/O Depleted

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

0.2

0.4

0.6

0.8

2.0

1.0

1 2 3 4 5 6Mass/Charge (AMU e-1)

m = -0.64 ± 0.05c = 0.63 ± 0.04

=4.39;P=2.56x10 -5

r = -0.92; p=7.8x10 -5

cu2

log(GI) = c + m*[MIQO/MOQI]

4He N

CO

NeMgSi

S

Ca Fe

M/Q-dependent depletion relative to “seed” population

Desai et al., 2004

IP shock vs. ambient

Apply this function to infer source abundances from measured LSEP values

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Comprises ~75%

impulsive SEP-like material

Inferred Source Abundances

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

SummaryFe/O decreases with energy up to ~60 MeV/n -

signature of shock acceleration

3He and heavy ions show large, variable, and unsystematic enhancements relative to SW values - Heavy ion abundances are not organized by a simple quantity wrt. SW values

Same M/Q-dependent enhancements are seen in IP shocks, LSEP events, and 3He-rich events

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Conclusion

The event-to-event variability in the ion composition in large SEP events at ULEIS energies can be attributed primarily to that of suprathermal seed population, most of which originates from processes similar to those occurring during 3He-rich SEP events.

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Large SEP events at ACE

64 large SEP events (NOAA’s SPE list) between 1997-Jan 2005

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Aug. 24, 2002

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Energy-dependence of C/O and Fe/OC/O ratios remain constant

with energy;Fe/O decreases by a factor of 2

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Same situation For 9 events with Fe/O <0.1 and upper limit 3He/4He

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Comparison with prior surveys

Fe/O at ULEIS energies are greater than prior surveys at higher energies

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Fe/O exhibits no clear solar cycle dependence

50% of events have finite 3He during 1998-2003

Occ. freq. drops below ~25% in 2004

Solar activity

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Fe/O ratio is poorly correlated with CME speed & flare longitude

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Event-integrated Fe/O vs.Mean Fe/O from 1 hr. averages

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Unlike for IP shocks, the Fe/O in LSEPs is not correlated with pre-event Fe/O on a case-by-case basis

Fe/O LSEPs vs. Pre-event

Desai et al. 2006; To appear in ApJ vol. 648 n1, Sep. 1, issue

Perhaps STEREO will help sample the seed population for some LSEP events