Evidence of Continuous Reconnection along a Helmet Streamer Current Sheet Observed by WISPR on Parker Solar Probe

Abstract

Parker Solar Probe's second solar encounter from 2019 March 30 to April 11 occurred during a period when the corona had a simple magnetic structure and relatively flat heliospheric current sheet (HCS), which was in the field of view of the Wide-field Imager for Solar Probe (WISPR) throughout. The images show an almost continual flow of transient density enhancements (streamer blobs) of various sizes near the latitude of the HCS during the entire 11 day encounter period. The high resolution and sensitivity of WISPR reveal the structure of some of the individual blobs not seen in observations from 1 au. Many of the blobs show dark central cores, suggesting that they are magnetic flux ropes. The 3D trajectories and sizes of four representative streamer blobs have been determined using the tracking and fitting technique of Liewer et al. (2020). Comparison of the location of these blobs with synoptic white-light maps for this time period, created using data from the Large Angle and Spectrometric Coronagraph (Brueckner et al. 1995) on board the Solar and Heliospheric Observatory, confirms that the blobs are at the location of the helmet streamer associated with the HCS. The blobs were observed in the region beyond 15 R ☉. The continual flow of blobs, the confirmation of their location at the HCS, and their flux-rope-like appearance provide strong evidence that the process of reconnection across the current sheet dominates the slow wind near the HCS.