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Type III Solar Radio Burst Source Region Splitting Due to a Quasi-Separatrix Layer  

Patrick McCauley   Submitted: 2017-11-14 21:21

We present low-frequency (80-240 MHz) radio imaging of type III solar radio bursts observed by the Murchison Widefield Array (MWA) on 2015/09/21. The source region for each burst splits from one dominant component at higher frequencies into two increasingly-separated components at lower frequencies. For channels below ~132 MHz, the two components repetitively diverge at high speeds (0.1-0.4 c) along directions tangent to the limb, with each episode lasting just ~2 s. We argue that both effects result from the strong magnetic field connectivity gradient that the burst-driving electron beams move into. Persistence mapping of extreme ultraviolet (EUV) jets observed by the Solar Dynamics Observatory reveals quasi-separatrix layers (QSLs) associated with coronal null points, including separatrix dome, spine, and curtain structures. Electrons are accelerated at the flare site toward an open QSL, where the beams follow diverging field lines to produce the source splitting, with larger separations at larger heights (lower frequencies). The splitting motion within individual frequency bands is interpreted as a projected time-of-flight effect, whereby electrons traveling along the outer field lines take slightly longer to excite emission at adjacent positions. Given this interpretation, we estimate an average beam speed of 0.2 c. We also qualitatively describe the quiescent corona, noting in particular that a disk-center coronal hole transitions from being dark at higher frequencies to bright at lower frequencies, turning over around 120 MHz. These observations are compared to synthetic images based on the Magnetohydrodynamic Algorithm outside a Sphere (MAS) model, which we use to flux-calibrate the burst data.

Authors: Patrick I. McCauley, Iver H. Cairns, John Morgan, Sarah E. Gibson, James C. Harding, Colin Lonsdale, and Divya Oberoi
Projects: None

Publication Status: Accepted by ApJ
Last Modified: 2017-11-15 12:19
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Prominence and Filament Eruptions Observed by the Solar Dynamics Observatory: Statistical Properties, Kinematics, and Online Catalog  

Patrick McCauley   Submitted: 2015-05-11 12:25

We present a statistical study of prominence and filament eruptions observed by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO). Several properties are recorded for 904 events that were culled from the Heliophysics Event Knowledgebase (HEK) and incorporated into an online catalog for general use. These characteristics include the filament and eruption type, eruption symmetry and direction, apparent twisting and writhing motions, and the presence of vertical threads and coronal cavities. Associated flares and white-light coronal mass ejections (CME) are also recorded. Total rates are given for each property along with how they differ among filament types. We also examine the kinematics of 106 limb events to characterize the distinct slow- and fast-rise phases often exhibited by filament eruptions. The average fast-rise onset height, slow-rise duration, slow-rise velocity, maximum field-of-view (FOV) velocity, and maximum FOV acceleration are 83 Mm, 4.4 hours, 2.1 km s-1, 106 km s-1, and 111 m s-2, respectively. All parameters exhibit lognormal probability distributions similar to that of CME speeds. A positive correlation between latitude and fast-rise onset height is found, which we attribute to a corresponding negative correlation in the average vertical magnetic field gradient, or decay index, estimated from potential field source surface (PFSS) extrapolations. We also find the decay index at the fast-rise onset point to be 1.1 on average, consistent with the critical instability threshold theorized for straight current channels. Finally, we explore relationships between the derived kinematics properties and apparent twisting motions. We find that events with evident twist have significantly faster CME speeds and significantly lower fast-rise onset heights, suggesting relationships between these values and flux rope helicity.

Authors: Patrick I. McCauley, Yingna Su, Nicole Schanche, Kaitlin E. Evans, Chuan Su, Sean McKillop, and Katharine K. Reeves
Projects: SDO-AIA

Publication Status: SoPh (in press)
Last Modified: 2015-05-12 13:59
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Type III Solar Radio Burst Source Region Splitting Due to a Quasi-Separatrix Layer
Prominence and Filament Eruptions Observed by the Solar Dynamics Observatory: Statistical Properties, Kinematics, and Online Catalog

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