The Dynamic Formation of Pseudostreamers

Abstract

Streamers and pseudostreamers structure the corona at the largest scales, as seen in both eclipse and coronagraph white-light images. Their inverted-goblet appearance encloses broad coronal loops at the Sun and tapers to a narrow radial stalk away from the star. The streamer associated with the global solar dipole magnetic field is long-lived, predominantly contains a single arcade of nested loops within it, and separates opposite-polarity interplanetary magnetic fields with the heliospheric current sheet (HCS) anchored at its apex. Pseudostreamers, on the other hand, are transient, enclose double arcades of nested loops, and separate like-polarity fields with a dense plasma sheet. We use numerical magnetohydrodynamic simulations to calculate, for the first time, the formation of pseudostreamers in response to photospheric magnetic-field evolution. Convective transport of a minority-polarity flux concentration, initially positioned under one side of a streamer, through the streamer boundary into the adjacent preexisting coronal hole forms the pseudostreamer. Interchange magnetic reconnection at the overlying coronal null point(s) governs the development of the pseudostreamer above-and of a new satellite coronal hole behind-the moving minority polarity. The reconnection dynamics liberate coronal-loop plasma that can escape into the heliosphere along so-called separatrix-web ("S-Web") arcs, which reach far from the HCS and the solar equatorial plane, and can explain the origin of high-latitude slow solar wind. We describe the implications of our results for in situ and remote-sensing observations of the corona and heliosphere as obtained, most recently, by Parker Solar Probe and Solar Orbiter.

The Dynamic Coupling of Streamers and Pseudostreamers to the Heliosphere

“…The separatrix surfaces of two of these nulls together form a dome that encloses closed magnetic flux (red field lines in Figure 1(a) at around 45°north, and in Figure 3), while a portion of the separatrix of the third (central) null extends as a separatrix curtain out into the heliosphere (Titov et al 2011). Both spine lines of the eastern and western null points are in the closed field region, meaning that the S-Web structure that partitions the flux of the polar and midlatitude coronal holes is formed entirely by this separatrix surface (Scott et al 2021). These properties are stable throughout the simulations.…”

“…The S-Web has been studied, in detail, in recent years (Antiochos et al 2011;Titov et al 2011;Crooker et al 2012;Scott et al 2018Scott et al , 2019Scott et al , 2021, and these studies have shown that there are two primary types of open/closed boundaries that contribute to this Web and, thereby, serve as sources of slow wind. One that is always present is the helmet streamer belt and associated heliospheric current sheet (HCS).…”

The Dynamic Coupling of Streamers and Pseudostreamers to the Heliosphere

“…3), while a portion of the separatrix of the third (central) null extends as a "separatrix curtain" out into the heliosphere (Titov et al 2011). Both spine lines of the eastern and western null points are in the closed-field region, meaning that the S-Web structure that partitions the flux of the polar and mid-latitude coronal holes is formed entirely by this separatrix surface (Scott et al 2021). These properties are stable throughout the simulations.…”

“…The S-Web captures all the separatrix and quasi-separatrix surfaces due to the open-closed boundary and, thereby, indicates possible locations for slow wind in the heliosphere. The S-Web has been studied, in detail, in recent years (Antiochos et al 2011;Titov et al 2011;Crooker et al 2012;Scott et al 2018Scott et al , 2019Scott et al , 2021, and these studies have shown that there are two primary types of open-closed boundaries that contribute to this Web and, thereby, serve as sources of slow wind. One that is always present is the helmet streamer belt and associated heliospheric current sheet (HCS).…”

The Dynamic Evolution of Solar Wind Streams Following Interchange Reconnection

“…For plasma that originates from within a closed domain to escape across the open-closed boundary into an adjacent coronal hole depends on the process of interchange reconnection (Crooker et al 2002), whereby field lines from either side of the open-closed boundary undergo a change in connectivity so that a new flux tube is formed that extends from a footpoint within a previously closed region on the solar surface out into the open coronal-hole region and into the heliosphere and beyond. This process has been studied extensively in 3D magnetohydrodynamic (MHD) simulations of coronal streamers and pseudostreamers (e.g., Masson et al 2014;Higginson et al 2017;Aslanyan et al 2021;Scott et al 2021); however, these and similar studies have invoked simplistic fluid approximations for computational efficiency. Therefore, while the magnetic evolution is reasonably well understood, many questions remain concerning the associated plasma dynamics.…”