Simulations of structured upflows from plumes and their connection to the solar wind

TL;DR

This work addresses how structured upflows from coronal-hole plumes contribute to the solar wind by examining magnetic topology with 3D radiative MHD simulations. Using the MURaM code, the authors embed a plume into a coronal-hole-like field, synthesize Fe X 174 Å emission, and analyze the interplay between cool lower-atmosphere downflows and hot coronal upflows guided by quasi-separatrix layers (QSLs) at the open-open interface. They find that intense QSL sheets at the OO-interface channel high-velocity, narrow-upflow plumes that persist with height and carry mass flux sufficient to sustain the solar wind, without requiring interchange reconnection at null points. These results suggest a topological pathway for wind acceleration via QSL-mediated reconnection along open flux boundaries, consistent with S-web structures and offering implications for interpreting plume-related EUV signatures from multiple viewing angles.

Abstract

Small-scale transient jetlet activity and associated upflows from coronal hole plumes are potential sources of the solar wind. To elucidate the magnetic origins and driving mechanisms of such upflows, we perform three-dimensional radiative magnetohydrodynamic simulations using the MURaM code, spanning from the upper convection zone to the low corona. We synthesize Fe\,{\sc x} 174\,Å emission to capture the plume evolution comparable to observations, examining underlying plasma flows, thermal structures, and magnetic topologies. We identify a pronounced transition from cool downflows in the lower atmosphere to hot upflows in the corona at the interface between plume-rooted like-polarity flux concentrations. These upflows are threaded by a complex, filamentary network of Quasi-Separatrix Layers (QSLs) -- a topology distinct from standard interchange reconnection scenarios. The domain-averaged mass flux over a 38-minute interval ranges from $10^{-9}$ to $10^{-8}\,\mathrm{g\,cm^{-2}\,s^{-1}}$, substantially exceeding observed solar-wind loss rates. Our results demonstrate that highly structured plasma outflows are channeled along strong QSLs at open--open field boundaries, providing a pathway to sustain the solar wind from coronal-hole plumes without requiring interchange reconnection triggered by opposite-polarity flux emergence.

Figures (9)

• Figure 1: MHD simulations of a plume. A snapshot of physical properties of the plume as defined by the concentrated positive polarity flux tube at the photosphere ($\tau_{500nm}\approx 1$) in our model. The full horizontal extent of the computational domain is shown. Panel (a): vertical component of the magnetic field, representing the photospheric magnetogram where P and P$'$ mark the plume and neighboring positive polarity patches respectively. Panel (b): vertical component of the flow velocity exhibiting the granulation pattern. Panel (c): density. Panel (d): temperature. The feature marked by green circle in all the panels is the photospheric footpoint of the plume. An animation of this figure is available online, illustrating the temporal evolution of all four quantities shown in panels (a)–(d) over 57 minutes of solar time at a cadence of 3.8 minutes. The real-time duration of the video is 8 s. See Section \ref{['subsec3p1']} for details.
• Figure 2: Limb or side-view of the coronal emission and flow structure showing the vertical expansion of the plume in our 3D MHD model. Left: coronal emission synthesized in EUI 174 Å filter, integrated along $y-$direction (displayed on the $xz-$plane) in the model. Right: vertical component of the flow velocity at $y \approx$ 23 Mm, on $xz-$plane. The ellipse on $v_{z}$ slice marks the upflows channeled at the boundary of plume.
• Figure 3: Disk-center or top-down view of the coronal emission and flow structure in our 3D MHD model. Left: coronal emission synthesized in EUI 174 Å filter, integrated along vertical direction ($z$) in the model. Right: vertical component of the flow velocity, time-averaged over approximately 18 minutes at 3 Mm height above the photosphere. The upflow structure at the plume boundary is enclosed within black rectangle. The green circles (same as Figure \ref{['fig1']}) in both the images mark the location of introduced plume. The dashed line is reference for a slice of $v_{z}$ map in Figure \ref{['fig3']}. See Section \ref{['subsec3p2']} for details. An animation combining the left panels of the current figure and Figure \ref{['fig2']} is available online. It illustrates the temporal evolution of synthesized coronal emission in EUI 174 Å filter, spanning approximately 38 minutes of solar time with a cadence of 22s. The real-time duration of the animation is 7 s. See Section \ref{['subsec3p2']} for details.
• Figure 4: Visualizing thermodynamics. Panel (a): vertical component of the velocity on a plane passing between two positive polarity patches of plume P and neighboring polarity P$'$ (blue denotes upflowing plasma and red denotes downflowing plasma). Panel (b): temperature (in $\log$ scale) on the same vertical plane. A transition from cool downflowing plasma to hot upward moving plasma is visible above a certain height. In each panel, the red, green, and blue arrows on bottom left indicate the $x$, $y$, and $z$-axes of the 3D Cartesian coordinate system, respectively. The bottom boundary is $B_z$ saturated between $\pm$400 G. An animation of this figure is available online, showing the temporal evolution of the displayed quantities over 38 minutes of solar time with a cadence of 3.8 minutes. The animation runs for 5 s in real time. See Section \ref{['subsec3p2']} for details.
• Figure 5: QSLs and magnetic structures shaping the flow and temperature profiles between two positive magnetic polarities P and P$'$ which form the interface between two open field regions. Panel (a): Direct volume rendering of the $\ln Q$ distribution, overlaid with magnetic field lines (black) originating from the two adjacent positive polarities, for the same field of view as in Figure \ref{['fig4']}. The surface corresponding to the very high value $\ln Q = 8$ (red) is located at the midplane, marking the interface formed by field lines from the two open field regions. Panel (b): Side view showing the inverted Y-shaped magnetic structure that forms the interface between the two positive polarities/open field regions. Panel (c): Top-down view of the QSLs displayed in panel (a), emphasizing the intricate fine structures. See Section \ref{['subsec3p3']} for further details.