SHINE 2001 Summer Workshop
SHINE 2001 Workshop Report published in Eos, 83, 24, 2002.
Solar-Heliospheric Group SHINE Sheds Light on Murky Problems
Like a flashlight beam in muddy water, attention focused on murky science issues scatters a great deal, but reveals broad features of fundamental importance for future progress. The value of this approach was apparent at a recent meeting of the Solar Heliospheric Interplanetary Environment (SHINE) community. SHINE held its third annual workshop this summer simultaneously with those of its sister organizations, Geospace Environment Modeling (GEM) and Coupling, Energetics, and Dynamics of Atmospheric Regions (CEDAR). All three meetings were held in close proximity and were sponsored by the National Science Foundation.
The kind of workshop environment provided by SHINE for solar and heliospheric physicists is unique. Staged exchanges between modelers and observers and between specialists in solar, energetic particle, and heliospheric physics strongly encourage participants to think about their own work in the context of larger issues. At SHINE 2001, these kinds of exchanges even extended to magnetospheric physicists at two joint sessions with GEM. The first addressed geomagnetic and energetic particle effects of CMEs and high-speed streams, and the second addressed ways in which CME and substorm modelers might share their expertise.
SHINE 2001 was organized into working groups addressing three broad topics: origins of coronal mass ejections (CMEs), their interplanetary manifestations, and solar energetic particles. In each group, concerted efforts were made to bridge the gap between modelers and observers. Focused questions returned a scattering of responses, revealing just how wide that gap can be, but they allowed the group to identify specific ways in which progress might be made, and provided the community with challenges for the coming year.
For example, in a discussion about the role of photospheric magnetic field evolution in the working group on CMEs, it quickly became clear that the types of evolution that differentiate CME models--emergence, shearing, convergence, and cancellation of magnetic flux--occur together during the period leading up to CMEs. It is not readily apparent which, if any, plays a dominant role. To make progress on this issue, the group decided to challenge the community to provide quantitative measures of each type of surface field evolution and to document their correlations with CMEs. Discussion of a similar issue regarding the timing and role of reconnection in CMEs resulted in a plan to organize a campaign of coordinated observations from specific events.
In a quest to understand CME origins and evolution, the group on interplanetary manifestations focused on the difference between simple and complex interplanetary CMEs (ICMEs). Participants discovered that definitions of these types vary widely and that observers can disagree substantially on what constitutes the boundaries of a given ICME. Questions were raised about the energetics and multiplicity of the source structures and the number and kinds of interplanetary structures involved in complex cases. As in the CME group, pushing ahead on campaigns to analyze specific events was offered as the best way to make progress in the coming year.
In addition, to highlight the topic, SHINE members convened a special SH session at AGU's 2001 Fall Meeting titled "Interacting CMEs and Their Relationships to Interacting Ejecta." Like the three well-attended special SH sessions organized by SHINE members for the 2001 Spring Meeting, the session was an effective way to accelerate research in this area. The SHINE 2001 workshop group also discussed the possibility of using interplanetary observations to distinguish between different models of CME initiation. Although existing models are still highly idealistic, the observers challenged the modelers to provide predictions for signatures in interplanetary space.
The group on solar energetic particles (SEPs) focused on SEP relationships to CMEs, inviting members of the other working groups to speak on how their expertise on CME dynamics and shock propagation could be applied to various SEP problems. A large number of complications were discussed, including those surrounding the ever-popular issue of the relative roles of flares and shocks in producing the high-energy ions in very large SEP events. The most heated debate centered on whether radio signatures indicate a larger role for flares in large particle events, which normally are assumed to be shock-accelerated.
Two additional topics discussed were the complications of re-acceleration of remnant energetic particles from preceding flare activity by subsequent CME-driven shocks, which can explain why many large CME-associated SEP events show characteristics traditionally associated with flare acceleration; and the possibility of improving on plane-of-sky projections as substitutes for true CME speeds (and hence shock characteristics) through modeling efforts based on Large Angle Spectrometric Coronagraph (LASCO) images.
Relevant to shock propagation, an important insight was discussed regarding the coronal Alfven speed profile. Near-Sun speeds are much lower than often thought, which allows the fastest CMEs to drive shocks there, and a local maximum at ~3.5 Rs can explain why most SEP-producing CMEs become efficient particle accelerators only beyond ~4 Rs. Fortified with new ideas stimulated by these discussions, SEP group members plan to make progress in the coming year primarily on data-based modeling projects.
SHINE 2001 was held June 17-21, 2001, in Snowmass, Colorado.
Next summer, SHINE 2002 will be held in Banff, Canada. Information about working group topics, registration and housing will appear on the SHINE Web site, http://www.sec.noaa.gov/shine.
This article is based in part on reports prepared by working group leaders J. Klimchuk, M. Popecki, P. Riley, A. Sterling, A. Tylka, and T. Zurbuchen. The complete reports can be found under "Meetings" at the SHINE Web site. SHINE 2001 and the preparation of this report were supported by the National Science Foundation under Grants ATM0000423 and ATM9805064. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.
Nancy Crooker, Center for Space Physics, Boston University, Boston, Mass., USA