Heavy Ion Abundances in Large Solar Energetic Particle Events Spring AGU 2006, SH43B-04
Post on 19-Mar-2016
46 Views
Preview:
DESCRIPTION
Transcript
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
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
top related