Solar Wind/SOHO 16

Session: Session 2: Particle Acceleration in the Sun and Heliosphere 1 (02)
Type: Oral presentation
Date: Monday, June 13, 2005
Time: 14:00 - 17:00

Seq   Time   Title   Abs No
1   14:00   Particle Acceleration in the Sun and Heliosphere
Giacalone, Joe
University of Arizona, UNITED STATES

Our current understanding of the acceleration of energetic charged particles of heliospheric origin will be reviewed. Because of the broad scope of this topic, much of the review will focus on the physics of diffusive shock acceleration. This mechanism naturally leads to power-law energy spectra which are commonly observed in the distributions of energetic particles in space plasmas. Both in situ and remote spacecraft observations of various heliospheric acceleration regions will be discussed. These include acceleration near the Sun and at CME-driven shock waves, propagating transient disturbances, corotating interaction regions, planetary bow shocks, and the heliospheric termination shock. Other acceleration mechanisms will be discussed only briefly. These include stochastic acceleration in turbulent electric and magnetic fields, parallel electric fields and magnetic reconnection as they apply to the origin of heavy ions associated with impulsive solar flares, and the origin of high-energy particles of magnetospheric origin. Open issues and unresolved questions, to stimulate future research, will be discussed throughout the review.

2   15:00   UV Observations Coronal Shock Waves
Raymond, John1; Ciaravella, A.2
1Center for Astrophsyics, UNITED STATES; 2Osservatorio Astronomico di Palermo, ITALY

Shock waves in the corona produce energetic particles, but it is not yet clear what controls the efficiency of particle acceleration. UVCS has observed about 10 shocks, of which 4 have been analyzed in detail. We summarize the properties of the pre-shock corona, the shock compression and particle heating derived from the UV spectra.

3   15:15   Relationship of Solar Flare Accelerated Particles to Solar Energetic Particles (SEPs) Observed in the Interplanetary Medium
Lin, Robert1; Shih, A. Y.1; Krucker, S.1; Share, G.2; Murphy, R.2; Smith, D. M.3; Mewaldt, R.4; Cohen, C. M. S.4; Looper, M. D.5; Mason, G.6; Haggerty, D. K.7
1University of California at Berkeley, UNITED STATES; 2Naval Research Laboratory, UNITED STATES; 3University of California at Santa Cruz, UNITED STATES; 4California Institute of Technology, UNITED STATES; 5The Aerospace Corporation, UNITED STATES; 6University of Maryland, UNITED STATES; 7Johns Hopkins University-Applied Physics Laboratory, UNITED STATES

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. We find that the numbers and spectra of the flare-accelerated energetic ions inferred for the gamma-ray line measurements are remarkably simlar to those of the SEPs measured in space for the well-connected 2 October 03 and 20 January 05 events. We discuss the implications for the particle acceleration and escape processes.

Pick, Monique1; Maia, D.2
1Observatoire de Paris-Meudon, FRANCE; 2CICGE, Observatorio, Universidade do Porto, PORTUGAL

The relation between near relativistic electrons detected in the interplanetary medium, CME development and flaring activity was discussed recently by different authors. We showed that the radio and the white light coronagraph observations support a scenario where the electrons are accelerated at coronal sites that originate in the wake of the magnetic restructuring linked to the CMEdevelopment. We review, in this presentation, the various kinds of acceleration sites which are built up during CME development and their association with energetic electron events. Expanding CME radio loops, in particular, are filled by electrons with energies of at least 1 MeV, accelerated in the low corona.

5   16:30   What Fraction of the CME Kinetic Energy Goes into Energetic Particles?
Mewaldt, R. A.1; Vourlidas, A.2; Mason, G. M.3; Haggerty, D. K.4; Looper, M. D.5; Cohen, C. M. S.1; Desai, M. I.3; Leske, R. A.1; Mazur, J. E.5

The largest solar energetic particle (SEP) events are believed to be accelerated by shocks driven by fast coronal mass ejections (CMEs). We compare measurements of the energy content of large SEP events to measurements of the kinetic energy of the associated CMEs in order to study the efficiency of this process. The CME kinetic energies were determined using data from the SOHO/LASCO coronagraph by measuring the CME velocity and estimating the total mass from its brightness. The largest SEP events are due to CMEs totaling ~10^32 ergs or more. The SEP energies were measured by combining data from instruments on ACE, SAMPEX, and GOES to obtain fluence spectra for H, He, and heavier elements over the energy range from ~0.1 to 100 MeV/nucleon. Electron spectra were measured from ~0.04 to 8 MeV. Fits to these spectra were corrected for the number of times particles cross 1 AU and integrated over the surface area through which SEPs escape into the outer heliosphere to obtain an estimate of the total energy content of accelerated particles. Data from seventeen events, based on published CME parameters, indicate that the ratio of the SEP to CME kinetic energies ranges from ~0.1% to ~20%, with the 10 largest SEP events in this sample giving an average SEP/CME kinetic-energy ratio of ~10%. Evidently shock acceleration is a relatively efficient process in these events. It is interesting that a similar efficiency is required for the acceleration of cosmic rays by supernova shocks in order to sustain the cosmic-ray energy density in the Galaxy. Work is now in progress to add additional events to this survey and to make improved estimates of the uncertainties in the SEP and CME energy determinations. We are also investigating whether the SEP acceleration efficiency correlates with other CME, SEP, or solar wind parameters.

6   16:45   Composition and Spectra from the October/November 2003 Energetic Particle Events
Cohen, C. M. S.1; Mason, G. M.2; Stone, E. C.1; Mewaldt, R. A.1; Leske, R. A.1; Looper, M. D.3; Desai, M. I.2; Cummings, A. C.1; von Rosenvinge, T. T.4; Wiedenbeck, M. E.5
1California Institute of Technology, UNITED STATES; 2University of Maryland, UNITED STATES; 3Aerospace Corporation, UNITED STATES; 4NASA/Goddard Space Flight Center, UNITED STATES; 5Jet Propulsion Laboratory, UNITED STATES

We present measurements of the composition and energy spectra for protons through iron from the extremely large solar energetic particle (SEP) events of October and November 2003. The combined data are from the EPAM, ULEIS and SIS instruments on ACE, the PET instrument on SAMPEX, and from GOES-11 and span more than 3 decades in energy. The event-integrated fluence spectra differ in shape from event to event with element-dependent spectral breaks which lead to energy-dependent composition. We discuss possible interpretations of these breaks in terms of rigidity- and diffusion- related effects. The spectra obtained around the passages of strong shocks during these SEP events are also examined within this framework.