Browsing by Author "Vourlidas, Angelos"

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How Does Magnetic Reconnection Drive the Early-stage Evolution of Coronal Mass Ejections?
(2020-04) Zhu, Chunming; Qui, Jiong; Liewer, Paulett; Vourlidas, Angelos
Theoretically, coronal mass ejection (CME) kinematics are related to magnetic reconnection processes in the solar corona. However, the current quantitative understanding of this relationship is based on the analysis of only a handful of events. Here we report a statistical study of 60 CME-flare events from 2010 August to 2013 December. We investigate kinematic properties of CMEs and magnetic reconnection in the low corona during the early phase of the eruptions, by combining limb observations from STEREO with simultaneous on-disk views from SDO. For a subset of 42 events with reconnection rate evaluated by the magnetic fluxes swept by the flare ribbons on the solar disk observed from SDO, we find a strong correlation between the peak CME acceleration and the peak reconnection rate. Also, the maximum velocities of relatively fast CMEs (≳600 km s−1) are positively correlated with the reconnection flux, but no such correlation is found for slow CMEs. A time-lagged correlation analysis suggests that the distribution of the time lag of CME acceleration relative to reconnection rate exhibits three peaks, approximately 10 minutes apart, and on average, acceleration-led events have smaller reconnection rates. We further compare the CME total mechanical energy with the estimated energy in the current sheet. The comparison suggests that, for small-flare events, reconnection in the current sheet alone is insufficient to fuel CMEs. Results from this study suggest that flare reconnection may dominate the acceleration of fast CMEs, but for events of slow CMEs and weak reconnection, other mechanisms may be more important.
Structure of the Plasma near the Heliospheric Current Sheet as Seen by WISPR/Parker Solar Probe from inside the Streamer Belt
(IOP Publising, 2023-05) Liewer, Paulett C.; Vourlidas, Angelos; Stenborg, Guillermo; Howard, Russell A.; Qiu, Jiong; Penteado, Paulo; Panasenco, Olga; Braga, Carlos R.
Parker Solar Probe (PSP) crossed the heliospheric current sheet (HCS) near the perihelion on encounters E8 and E11, enabling the Wide-field Imager for Solar Probe (WISPR) to image the streamer belt plasma in high resolution while flying through it. With perihelia of 16 R⊙ and 13 R⊙ for E8 and E11, respectively, WISPR images enable investigation of the structure of density encasing the HCS at much higher resolution than reported previously. As PSP flies closer to the Sun, fine-scale structures are resolved within the coronal rays of the streamer belt. Near the HCS, WISPR observes a fan of rays of various sizes and brightnesses, indicating large density variations in the HCS plasma sheet transverse to the radial direction. Near the perihelion, when PSP's speed exceeds the solar corotation speed, some rays exhibit large changes in apparent latitude as the HCS is encountered, and rays pass over and under the spacecraft. The multiple viewpoints provided during the HCS crossing enable us to extract the coordinates of a few rays in a heliocentric frame. The rays were found to lie near the HCS from a PFSS model. We compare their locations to the location of the streamers as seen in synoptic maps from the Large Angle and Spectrometric Coronagraph, and find that the rays generally fall within the bright streamer bands seen in these maps, which confirms that they are features of the streamer belt plasma. We speculate that the density variations in the helmet streamer plasma result from continuous interchange reconnection along the coronal hole boundaries.