Location
The 2001 SHINE Workshop was held in Snowmass, Colorado from June 17 – 21.
The SHINE 2001 Workshop, was held concurrently with the annual CEDAR/GEM meetings in Colorado. The SHINE workshop took place in Snowmass, in a facility adjacent to the GEM conference area.
SHINE 2001 Workshop Report in EOS
A report on SHINE 2001 was published in Eos, Vol. 83, No. 3,15 January 2002.
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2002EO000018
Working Group Reports
Working Group I (CMEs)
Working Group 1 (Coronal Mass Ejections) continued to pursue a main theme from last year’s workshop: observational tests of competing CME initiation models. We focused our attention on two rather specific topics that were identified last year and that appear in our matrix of predicted observables (http://umbra.nascom.nasa.gov/shine/cme_models.html).
In question form, they are:
1. What is the role of photospheric magnetic field evolution in causing CMEs?
a. Is there a gradual buildup phase involving the emergence, shearing, or convergence and cancellation of magnetic flux, as envisioned in “storage and release” type models?
b. Are there real-time changes in the photospheric field during the eruption, as envisioned in “dynamo” type models?
2. What is the role of magnetic reconnection in the eruption process?
a. Does reconnection, as evidenced by strong heating for example, occur before or after the eruption begins?
b. Is the reconnection located above or below the primary erupting structure (sheared core field or flux rope)?
The two topics were introduced in the excellent introductory talk by Zoran Mikic and were then addressed separately during the first two working group sessions. These sessions consisted of lively discussion centered around invited presentations. The discussion continued during the third and final session, which included short presentations from three young CME modelers (B.C. Low being young at heart!).
Most of the invited presentations were concerned with observations, and it quickly became apparent that there is no easy answer to the above questions. Movies of photospheric magnetograms reveal that many different types of surface field evolution occur together during the period leading up to CMEs: emergence, cancellation, shearing, convergence, etc. It is not readily apparent which, if any, plays a dominant role in the energy buildup and triggering of eruptions. Sizable magnetogram changes are not generally observed while CMEs are taking place (at least not in the several examples presented), but disagreement about what the dynamo models predict prevented us from making a definitive assessment of their viability.
Similarly, the question of when reconnection occurs is a challenge, but it is now possible to better identify effective methods to address this issue. From the theoretical standpoint, the question hinges on whether reconnection occurs early in the highly-sheared core region, early in a region far-removed from the core, or if early reconnection does not occur at all (i.e., eruptions due to some non-resistive process, with reconnection only occurring after eruption onset). Based on the presentations at this meeting, there is some evidence that CMEs show early evolution prior to flare brightenings, based on comparisons with LASCO, EIT, and GOES data. Also, there are cases where CME-associated dimmings in EIT are seen well before other eruption signatures. These results may be implying that eruptions are occurring at an early stage without a substantial reconnection signature. Another view, however, comes out of H-alpha observations which show Doppler motions in the neighborhood of filaments that are about to erupt; these observations may suggest that reconnection episodes occur prior to the onset of substantial soft X-ray emission.
The last working group session included discussion of a third topic–the the pre-eruption coronal magnetic field structure–which also appears in the matrix of predicted observables from SHINE 2000. The basic question is whether a twisted flux rope is present before the eruption begins or whether it forms during the eruption process. There was no concensus.
An outcome of our deliberations was a list of challenges for the coming year(s):
1. Develop QUANTITATIVE measures of flux cancellation, flux emergence, and shear flow, and determine whether they are correlated with CMEs.
2. Investigate the location and timing of magnetic reconnection relative to the onset of CMEs, using coordinated observations from a variety of sources, including H-alpha, EUV, and X-ray images.
3. Determine observationally the pre-eruption coronal magnetic structure (e.g., flux rope or sheared core field).
4. Model a real event based on time-dependent photospheric boundary conditions from observations.
5. Determine whether CMEs are global phenomena (i.e., are a result of evolutionary changes involving a major fraction of the photosphere
and corona).
In summary, Working Group 1 had an enjoyable and productive time in Snowmass!
Working Group II
SHINE 2001
The general task of working group 2 at the SHINE 2001 workshop was to investigate the interplanetary connections of solar transient activity. In particular, our aim was to address (in each of the three half-day sessions) the following topics: (1) Complex versus simple CMEs; (2) Model predictions; and (3) Are there two classes of (interplanetary) CMEs?
Session 1 (complex versus simple CMEs) was introduced by Len Burlaga, who in an invited review during the plenary session, laid the groundwork for interpreting interplanetary ejecta as either simple (cloud-like) or complex (non-cloud-like). He discussed the difficulties in identifying ejecta boundaries and suggested how best to locate them. He proposed two possible evolutionary paths for simple CMEs into complex CMEs. In the first, two or more CMEs interact with each other between the Sun and the Earth, resulting in a complex structure. In the second, some instability develops within the ejecta producing a complex ejecta.
During the first session presentations were made by Dave Webb and Ian Richardson on complexity within CMEs. Richardson summarized common interpretations of “complex ejecta,” pointing out that the term was sufficiently different to different groups that virtually all CMEs could be considered complex! Webb illustrated this by noting that one of the events in the working group’s preliminary candidate list of simple CMEs was also listed in the list of complex CMEs. Nat Gopalswarmy presented an analysis of Radio burst measurements also suggesting that complex CMEs may be produced by the interaction of two or more ejecta. Short presentations summarizing datasets for a preliminary list of “compaign” events were made by Mike Andrews, Garath Lawence, Len Burlaga, Dave Webb, and John Steinberg.
These presentations stimulated several relevant discussions, one of which concerned the importance and difficulties associated with identifying ejecta boundaries. Using the event identified as both “simple” and “complex,” we realized that its initial designation as complex relied on a questionable interpretation of where counterstreaming suprathermal electrons (CSEs) were present during the interval. On closer inspection we were able to move the rear boundary forward in time, making the ejecta “simple,” and resolving the apparent discrepancy. The discussions then moved to the question of what makes a complex CME complex? Are complex CMEs just “composite” CMEs, produced from the interaction of two or more ejecta? Are they “born” that way? Do they evolve from a simpler configuration via some instability? A complementary question was also posed: What makes a simple CME simple? Are they also born that way? Do they evolve from a more complex low-beta configuration through relaxation? Is the only distinction between complex and simple ejecta an observational selection effect: Does the trajectory of the spacecraft through the ejecta dictate whether we observe a “simple” or “complex” CME? Needless to say, we did not arrive at any definitive answers to these questions! What we did learn though is that any CME will be complex if you don’t understand it!
In session 2 we turned our attention to the question of what the modellers would/could predict in solar and/or in situ observations of CMEs, particularly with regard to differentiating features between the models. Presentations were made by Jim Klimchuk, Paul Bellan, Jon Linker, Jack Gosling, Spiro Antiochos, Jonathan Krall, and Vic Pizzo. Although the idealized nature of the models generally precluded such predictions, Klimchuk ventured that while there is, in principle, no limit to the degree of twist in a flux rope produced in the “breakout” model, a maximum of 2-3 turns is all that can be produced in the “flux rope” model. We discussed whether the models would place prominence material at different locations in relation to the flux rope and how this fit with in situ composition measurements that suggest cold material is sometimes present at the back of the flux rope, while in other cases, it is present at the front. The importance of prominence material (perhaps containing as much mass as the CME itself) was discussed and Antiochos argued that a fundamental distinction between the “breakout” and “flux rope” models was that in the latter, either all or none of the prominence material must be ejected. We also asked whether the formation of a flux rope is a necessary part of models, which it apparently is. In a generalization of the topic of associating the “three part structure” seen in coronagraph observations with in situ structures, we discussed the topology of magnetic field lines, as inferred from the signature of CSEs. Linker pointed out that the presence of an overlying arcade might translate into CSEs preceding the flux rope, whereas heat flux dropouts (suggesting the complete disconnection of field lines) should trail the ejecta. Gosling emphasized that this picture would likely be complicated since the reconnection was expected to occur in a patchy fashion along the neutral line. Finally, Pizzo discussed the significant interaction of the ambient solar wind with the ejecta, and to what degree the flux rope would maintain its integrity.
In the third, and final session for working group 2 we returned to a “challenge question” posed at the end of the SHINE 2000 workshop, namely, are there two classes of CMEs? To address this, we began with presentations from Mike Andrews, David Alexander, and Seiji Yashiro. This topic had formed the basis of a special session at the Spring AGU, and a consensus view had already formed that while two classes may exist, the now infamous “Sheeley Plot” may not be the best place to start. As Alexander pointed out, to really try to resolve this from a kinematic perspective, we need acceleration profiles at lower altitudes. Andrews argued that mass and energy are better delineators than velocity profiles and Thomas Zurbuchen suggested that we might compare in situ “conserved” quantities with solar observations. To make further progress on some of the topics discussed at the workshop, we agreed to screen the original list of campaign events. In particular, a subgroup of the participants will identify 4 events: a “simple” event that drives a shock and one that does not, and a “complex” event that drives a shock and one that does not. We completed the session by defining some “challenges” to be addressed during the upcoming year. Our first challenges are directed at the solar modellers: (1) to provide differentiating observational signatures predicted from their models; and (2) to model a non-flux rope CME. For ourselves, we posed the following question: What are the origins of complexity within CMEs?