SPA-Solar and Heliospheric Physics General Contributions III
Presiding: T H Zurbuchen, Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan; J T Steinberg, Los Alamos National Laboratory
SH33A-01 13:30h
Comparison between impulsive 3He-rich events and energetic electron events
Impulsive solar energetic particle (SEP) events with large enrichments of 3He are associated with ~2-100 keV impulsive electrons. Electron observations with the energy range of ~3 eV - 500 keV by the WIND 3-D Plasma and Energetic Particle experiment (3DP) and ion measurements with the energy range of ~ 0.02 - 10 MeV/nucleon by the ACE Ultra-Low Energy Isotopic Spectrometer (ULEIS) provide the first possibility of an accurate timing comparison of between impulsive 3He-rich events and energetic electron events. We select eleven solar impulsive events with enhanced 3He/4He ratios (~0.1 - 1.5) and a clear velocity dispersion of both ion and electron events over a wide energy range. We remove the contaminations of higher energy electrons in Solid State Telescopes (SST) on WIND, determine the interplanetary path length from peak times of WIND electron data observed in situ, and obtain the electron injection profiles at the Sun from triangular fits to in situ observations. The onsets and peaks of the injection of 3He-rich ion events at the Sun are derived from those of ACE ion data observed in situ by taking into account the travel time along the path length comparable to electron events. The comparison study shows a systematic delay of the injection of 3He-rich ions events with respect to the injection of electron events. Nine of ten events have a fast (> 570 km/s) west CME observed by SOHO/LASCO with the onset of electron injection close to the origin of the CME, and with the onset of ion injection corresponding to a median height ~ 5 Rs of CME.
SH33A-02 13:45h
Relationship of Solar Flare Accelerated Particles to Solar Energetic Particles (SEPs) Observed in the Interplanetary Medium
Observations of hard X-ray/gamma-ray continuum and gamma-ray lines produced by energetic electrons and ions, respectively, colliding with the solar atmosphere, have shown that large solar flares can accelerate ions up to many GeV and electrons up to hundreds of MeV. Solar energetic particles (SEPs) are observed by spacecraft near 1 AU and by ground-based instrumentation to extend up to similar energies in large SEP events, but it is believed that a different acceleration process associated with fast Coronal mass Ejections (CMEs) is responsible. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) mission provides high-resolution spectroscopy and imaging of flare hard X-rays and gamma-rays. Such observations can provide information on the location, energy spectra, and composition of the flare accelerated energetic particles at the Sun. We compare the RHESSI observations of the 2003 October 28, 2003 November 2, and 2005 January 20 flares with both energetic electron and ion observations near 1 AU from ACE, SAMPEX, Wind,and GOES spacecraft, and discuss the implications for the particle acceleration and escape processes
SH33A-03 14:00h
Solar Electron Bursts Observed Below 1.4 keV by ACE and Genesis: Characteristics and Implications for Particle Transport
Solar active processes frequently produce electron bursts at energies below 1.4 keV. The characteristics of these solar electron bursts vary considerably from event to event due to the physical processes involved in their acceleration and propagation to Earth. Previous observations have shown that some bursts have a broader pitch-angle distribution than the preceding strahl distribution, suggesting that propagation effects are important for understanding 1 AU observations. We present a study of the pitch-angle distributions of suprathermal electrons observed by ACE and Genesis before, during, and after solar bursts. We report the fraction of burst beams that broaden, the conditions under which they broaden, and the energy dependence of the burst beam width. We find that most long duration, high intensity bursts broaden. We often find a delay in the onset of burst beam broadening relative to the burst onset. The fact that some bursts broaden relative to the preceding strahl suggests that broadening occurs by a self-generated process. The facts that high intensity bursts broaden preferentially and that broadening is delayed suggest that this process has a threshold level.
SH33A-04 14:15h
Composition and Ionic Charge State Measurements of the Large Solar Particle Event of 20 January 2005
The 20 January 2005 solar event was observed as a large ground-level event by neutron monitors and as a large solar energetic particle event by spacecraft, with particle spectra comparable to the hardest events of solar cycle 23. We will present composition and ionic charge state measurements for this event using data from instruments aboard the ACE and SAMPEX spacecraft. These results will include species from H to Fe spanning the energy range from ~0.1 to ~300 MeV/nuc. A new analysis of penetrating particles has been used to extend the ACE/SIS heavy-ion spectra to higher energies (e.g. up to 300 MeV/nuc) in order to investigate the possibility of high-energy spectral rollovers. The charge state measurements have been obtained from SAMPEX data, using the geomagnetic rigidity-filter technique in the energy range from ~30 to ~90 MeV/nuc. We will compare the composition and charge state measurements for this event with measurements of other large events from the past solar cycle, including possible correlations between the elemental and ionic charge state composition.
SH33A-05 14:30h
A Search for Relativistic High-Energy Protons From the Extreme Solar Flares of 2000-03
We applied a high-energy proton flux-measuring tool based on detection of the energy deposited by post-flare protons in the active silicon layers of the SOHO/EIT and TRACE CCDs to extract individual proton events from the Fe XII (19.5~ nm) spectral line solar images. Temporal profiles of proton flux for extreme solar flares of 2000--03, including their pre-flare, impulsive phase, and near-post-flare intervals were analyzed in proton energy ranges 40--400 MeV. Both time and energy distributions of post-flare protons may be interpreted as the presence of relativistic (c/3 -- c/2 velocity at 1 A.U.) protons in some post-flare fluxes.
SH33A-06 14:45h
Injection and Propagation of Shock-Associated Solar Energetic Particles
It has long been known that during the initial portion of shock-associated solar energetic particle (SEP) events, different species of particles sometimes show differences in the rise portion and time to maximum at 1 AU. The effect is more pronounced at energies below a few MeV/nucleon. Under the paradigm that SEPs are all accelerated in a single stage near the Sun, this behavior has been modeled by invoking a rigidity dependence of the interplanetary scattering mean free path. Using the more recent paradigm that shock-associated SEPs are accelerated over a considerable spatial scale of perhaps distances of up to 10s of solar radii, these differences in the onset and rise to maximum may be due to the effects of acceleration and release time scales at the shock, with little influence from interplanetary propagation. Distinguishing between these two paradigms is important for understanding and correctly modeling SEPs. ACE spacecraft observations for large particle events during the recent solar maximum have made it possible to re-visit this problem over a broader energy range and with greater sensitivity than hitherto possible. The current study examines whether ACE observations are consistent with a simple model of particle release at the Sun over a finite period, followed by interplanetary propagation. By using multiple species and a broad energy range, we can investigate whether such a simple model can fit the data for typical events.