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Working Group 1 (Coronal Mass Ejections), led by Jim Klimchuk and Joe Gurman, addressed three main questions during the SHINE 2000 meeting in Lake Tahoe:

1. What is the observational evidence for multiple classes of CMEs?

2. What are the fundamental physical differences among the various CME initiation models that have been proposed?

3. What are the key observations that can discriminate among the models?

Progress was made on all of these questions, especially the last (see below), but in the end it was clear that much more work needs to be done before definitive answers are available. This "work in progress" status is reflected in the three challenges that we set for ourselves for the coming year:

1. Determine observationally whether there are two distinct classes of CMEs, as possibly suggested by acceleration profiles.

2. Better define and quantify the observational predictions of the models.

3. Devise and execute focussed observational studies to test the models.

1. The models

1. Breakout ( Antiochos 1998; Antiochos, DeVore, and Klimchuk 1999)

2. Flux Rope ( Forbes and Isenberg 1991; Amari et al. 2000; Wu et al. 2000)

3. Tether Cutting ( Sturrock et al. 1984; Moore et al. 2001)

4. Flux Injection ( Chen 1989; Krall, Chen, and Santoro 2000)

5. Mass Loading ( Wolfson and Saran 1998; Low 1999).

2. The observables

1. Is a multipolar magnetic field required, or is a simple bipolar field sufficient?

2. Does the pre-eruption configuration necessarily contain a flux rope?

3. Must the field be appreciably sheared near the neutral line?

4. Must there be a converging flow toward the neutral line in the period leading up to the eruption?

5. Is reconnection required, and if so, does it occur before or after the onset of the eruption? (This refers to vigorous reconnection with strong heating.)

6. Does the reconnection take place above or below the sheared core field/flux rope/prominence?

7. Are there requirements on the existence and/or distribution of mass?

3. The matrix

² Amari et al. (2000)

4. References

Amari, T., J. F. Luciani, Z. Mikic, and J. Linker, A twisted flux rope model for coronal mass ejections and two-ribbon flares, Astrophys. J. (Lett.), 529, L49-L52, 2000

Antiochos, S. K., The magnetic topology of solar eruptions, Astrophys. J. (Lett.), 502, L181-L184, 1998

Antiochos, S. K., C. R. DeVore, and J. A. Klimchuk, A model for solar coronal mass ejections, Astrophys. J., 510, 485-493, 1999

Chen, J., Effects of toroidal forces in current loops embedded in a background plasma, Astrophys. J., 338, 453-470, 1989

Forbes, T. G., A review on the genesis of coronal mass ejections, J. Geophys. Res., 105, 23153-23165, 2000

Forbes, T. G., and P. A. Isenberg, A catastrophe mechanism for coronal mass ejections, Astrophys. J., 373, 294-307, 1991

Klimchuk, J. A., Theory of Coronal Mass Ejections, in Space Weather (AGU Monograph Series), edited by P. Song, G. Siscoe, and H. Singer, AGU, Washington, 2000, in press

Krall, J., J. Chen, and R. Santoro, Drive mechanisms of erupting solar magnetic flux tubes, Astrophys. J., 539, 964-982, 2000

Low, B. C., Coronal mass ejections, flares, and prominences, in Solar Wind Nine, CP471, edited by S. R. Habbal, R. Esser, J. V. Hollweg, and P. A. Isenberg, pp. 109-114, Am. Inst. Physics, Woodbury, NY, 1999

Moore, R. L., A. C. Sterling, H. S. Hudson, and J. R. Lemen, Onset of the magnetic explosion in solar flares and coronal mass ejections, to be published in Astrophys. J., 2001.

Sturrock, P. A., P. Kaufman, R. L. Moore, and D. F. Smith, Energy release in solar flares, Solar Phys., 94, 341-357, 1984

Wolfson, R., and S. Saran, Energetics of coronal mass ejections: role of the streamer cavity, Astrophys. J., 499, 496-503, 1998

Wu, S. T., W. P. Guo, S. P. Plunkett, B. Schmieder, and G. M. Simnett, Coronal mass ejections (CMEs) initiation: models and observations, J. Atm. and Solar Terrestrial Phys., in press, 2000