Abstract
Abstract The physical mechanisms that produce the slow solar wind are still highly debated. Parker Solar Probe’s (PSP’s) second solar encounter provided a new opportunity to relate in situ measurements of the nascent slow solar wind with white-light images of streamer flows. We exploit data taken by the Solar and Heliospheric Observatory, the Solar TErrestrial RElations Observatory (STEREO), and the Wide Imager on Solar Probe to reveal for the first time a close link between imaged streamer flows and the high-density plasma measured by the Solar Wind Electrons Alphas and Protons (SWEAP) experiment. We identify different types of slow winds measured by PSP that we relate to the spacecraft’s magnetic connectivity (or not) to streamer flows. SWEAP measured high-density and highly variable plasma when PSP was well connected to streamers but more tenuous wind with much weaker density variations when it exited streamer flows. STEREO imaging of the release and propagation of small transients from the Sun to PSP reveals that the spacecraft was continually impacted by the southern edge of streamer transients. The impact of specific density structures is marked by a higher occurrence of magnetic field reversals measured by the FIELDS magnetometers. Magnetic reversals are associated with much stronger density variations inside than outside streamer flows. We tentatively interpret these findings in terms of magnetic reconnection between open magnetic fields and coronal loops with different properties, providing support for the formation of a subset of the slow wind by magnetic reconnection.
Highlights
The solar wind plasma measured in situ has been classified into several different categories that could be related to different coronal sources (e.g., Xu & Borovsky 2015)
We present the Solar and Heliospheric Observatory (SOHO), Solar TErrestrial RElations Observatory (STEREO), and PSP images of bright structures expelled by helmet streamers in the direction of PSP
We find evidence that the reversals of the magnetic field lines detected by FIELDS occur in bursts or clumps when they originate in streamer flows, and are sometimes accompanied by significant density variations
Summary
The solar wind plasma measured in situ has been classified into several different categories that could be related to different coronal sources (e.g., Xu & Borovsky 2015). Synthetic white-light images produced by three-dimensional (3D) coronal models provide a good representation of the extent of streamer rays and the HPS (e.g., Pinto & Rouillard 2017; Poirier et al 2020) In such simulations, the dense coronal regions result from the properties of magnetic field lines that are directly adjacent to the helmet streamer. The excess density observed around the current sheet is related to a reconvergence of flux tubes near the top of helmet streamers This produces a very slow and dense wind along the rays extending above streamer tops, which forms the HPS (e.g., Wang 1994; Pinto & Rouillard 2017). We discuss the possible origins of these features at the Sun by considering STEREO EUV images
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