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Coronal Prominence Cavities: Magnetism and Dynamics. Sarah Gibson, Giuliana de Toma , Therese Kucera , Kathy Reeves, Donald Schmit , and Alphonse Sterling. Abstract.
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Coronal Prominence Cavities: Magnetism and Dynamics Sarah Gibson, Giuliana de Toma, Therese Kucera, Kathy Reeves, Donald Schmit, and Alphonse Sterling
Abstract Coronal mass ejections (CMEs) and associated prominence eruptions are spectacular manifestations of the Sun's magnetic energy. Elliptical regions of rarefied density, or cavities, are commonly observed surrounding coronal prominences, both quiescent and erupting. The prominence-cavity system is structured by magnetism, providing clues to to the processes that destabilize these equilibria and drive CMEs. The broad spectral coverage and high temporal cadence of cavities and associated eruptions obtained by the Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO/AIA) provide an important new window onto the magnetic structure of cavities, and onto their association with CMEs. We present observations of erupting cavities and discuss how they constrain and motivate magnetic models of the prominence, cavity, and CME. Please see poster by Schmit et al. for a discussion of how AIA dynamics observed in non-erupting cavities shed light on their magnetic structure.
Cavities erupting as CMEs A long-standing question is whether magnetic flux ropes exist before a CME, or whether they are created during the eruption; this is important because different CME triggers arise from the different magnetic topologies (Forbes et al. 2006). The classic observed “three-part” morphology of a bright expanding loop, followed by a relatively dark cavity, and lastly a bright core associated with an erupting prominence is universally cited as evidence for the CME possessing magnetic flux rope topology during eruption(Low and Hundhausen 1995; Plunkett et al. 2000; Lynch et al. 2004). Some three-part CMEs have been observed to erupt from precursor three-part quiescent prominence cavities(Sterling and Moore 2004; Gibson et al. 2006; Maricic et al. 2009). It has long been argued that, in these cases, a magnetic flux rope must be present before eruption (Low 1996). The stability of these quiescent cavities is thus intrinsically tied to the question of how they may erupt. To probe possible trigger mechanisms for CMEs, we plan to examine the evolution of cavity size, shape, height, and depletion prior to eruption. In this poster, we present a few examples of SDO/AIA cavities that erupt as CMEs, which is the beginning of a list of events for future studies of cavity magnetism and dynamics.
Examples of AIA erupting cavities *Mk4 not yet recalibrated
January 12, 2011 (See talk by D. Seaton on this event)
Cavity magnetism: Magnetic flux rope Fan & Gibson (2006) simulation of an equilibrium flux rope. (Left) forward-modeled AIA 284 A; (Right) sample magnetic fieldlines.
Cavity magnetism: CoMP polarization Dove et al. 2011 compare a magnetic model of a cavity (right) (Gibson and Low 1998) directly to observations of the coronal magnetic field (left). MLSO/CoMP measures Stokes parameters of the infrared forbidden lines of Fe XIII (Tomczyket al. 2008). Observations of a cavity taken by CoMP in 2005 showed a bright ring of linear polarization surrounding a region where the linear polarization strength was relatively depleted. Linear polarization is sensitive to POS magnetic field, so a “polarization ring” is consistent with magnetic field winding around a central line-of-sight-oriented axis.
Next steps We plan to continue to expand this list, and to obtain Mk4 and CoMP data as they become available (both are currently undergoing calibration -- CoMP data available starting October 2010) Then we will ask the following questions: • What is the evolution of cavities prior to eruption? • Do they change in size, shape, contrast? If so, on what time scale(s)? • Do polarization signals change prior to/during eruptions? • Are hot cores more likely to be present/more visible just prior to eruption? • Under what circumstances are prominences surrounded by the cavity as opposed to lying below (like a lollypop stick)? • Do cavities have more flows, both LOS and POS, prior to an eruption? • What are the spatial/temporal correlations between prominence and cavity structures and motions? • What do these observations teach us about stability and eruptive triggers?
