OBJECTIVE: To determine the causes and energetics of explosive events in the solar transition region, and to look for coupling of these events to the chromosphere and corona.
SCIENTIFIC BACKGROUND: Explosive events are ubiquitous, reconnection-driven line broadenings in the transition region, 1.5-5 Mm in size, lasting from a few seconds to a few minutes (Dere et al. 1991; Innes et al. 1997; and references therein). Few have been imaged, but there is evidence that EEs are much more complex than the bipolar jet model (Fox, Kankelborg & Thomas 2010; Innes & Teriaca 2013). Some preliminary IRIS observations are shown in figure 1. This IRIS campaign would spatially and temporally resolve many events, observe events down to $sim 300$,km scales, and look for chromospheric and coronal coupling. Explosive events are observed in a variety of different solar conditions, but they often involve small bipoles and/or occur near neutral lines. We hope to determine what magnetic situations give rise to reconnection, the rates and timescales of reconnection, how much energy is released, and the degree to which the events couple to the corona and the chromosphere.
Explosive events are a laboratory to probe reconnection physics. Since the reconnection occurs in transition region plasma, the emission measure is high, the event is localized along the line of sight, and it should be possible to observe the reconnection region itself, as well as inflows and outflows, routinely. We anticipate a very high event rate for this study. Figure 2 compares a cartoon of tearing mode reconnection to observations obtained with the MOSES rocket payload in February 2006 (Fox et al. 2010).
The magnetic context is essential to understanding the nature of these events. Ideally, the magnetic field would be measured in the chromosphere, where it is presumed to be nearly force free, so that extrapolation to the transition region and corona will be more accurate.
Observations are desired with approximately 1-hr duration in a variety of solar conditions, particularly near neutral lines in both quiet sun and quiescent active regions. We particularly desire observations in May (to collect data that will be used by REU students at MSU beginning June 9) and August (coordinated with the MOSES-II rocket flight, launch date TBD, near noon MDT).
Dere, K. P., Bartoe, J., Brueckner, G. E., Ewing, J., & Lund, P. 1991, J. Geophys. Res., 96, 9399
Fox, J. L., Kankelborg, C. C., & Thomas, R. J. 2010, ApJ, 719, 1132
Innes, D. E. & Teriaca, L. 2013, Sol. Phys., 282, 453
Innes, D. E., Inhester, B., Axford, W. I., & Wilhelm, K. 1997a, Nature, 386, 811