Dynamics of Streamers and Pseudostreamers and Implications for the Solar Wind

TL;DR

The paper addresses how interchange reconnection between closed and open flux in the corona contributes to the Sun's slow wind and its variability, focusing on helmet streamers and pseudostreamers. It employs a global 2.5D MHD model extending from the chromosphere to $30R_\odot$, with self-consistent thermodynamics, anisotropic conduction, and radiative cooling, solved with MPI-AMRVAC. The results reveal a quasi-periodic 'breathing' of helmet streamers with plasmoids released along the heliospheric current sheet and a back-and-forth interchange reconnection on the pseudostreamer flanks, driving hot, dense plasma into open field. Synthetic in-situ densities show periodic and bursty signatures consistent with Parker Solar Probe observations, supporting continual plasma release into the heliosphere across the S-Web.

Abstract

The origin of the Sun's slow wind and its inherent variability remain unknown, but there is increasing evidence that interaction between closed and open magnetic flux in the corona plays a role. This paper studies the dynamic evolution of streamers and pseudostreamers with a particular focus on the release of plasma from the closed to the open field region. We employ a global magnetohydrodynamic model that extends from the solar chromosphere to 30 solar radii, and that extends previous interchange magnetic reconnection modelling by including self-consistent thermodynamics. We find that at both the helmet streamer and pseudostreamer there is a continual dynamic interaction between closed and open flux. At the helmet streamer, this takes the form of a ''breathing'' cycle in which the closed flux contracts and expands, and plasmoids are released along the heliospheric current sheet. The pseudostreamer exhibits a back-and-forth motion, driving interchange reconnection alternately on its opposite flanks. The resulting release of hot, dense plasma leads to density fluctuations in the open field that are significantly larger above the helmet streamer due to the persistence of the plasmoids there. Our model demonstrates that plasma is continually being released into the heliosphere from both streamers and pseudostreamers.

Figures (6)

• Figure 1: A global-scale plasma temperature map from the quasi-equilibrium state, at $t= 80$ hours of solar time. The associated magnetic field lines are visualized by the Line Integral Convolution (LIC) method.
• Figure 2: Temperature and density structures of the simulated Helmet streamer and Pseudostreamer at the quasi-equilibrium state at $t=80$ hours. Panel (a) is a close-up view of Figure \ref{['fig:globalmap']} showing the temperature, while panel (b) shows the number density profile.
• Figure 3: Variation of the radial flow speed and temperature of the solar wind with height (at t=80 hours). Black and blue curves represent radial outflow speed (left axis) measured near the north pole and along the helmet streamer stalk. respectively. Temperature profile (right axis) near the polar region and along the same streamer stalk are shown with green and red lines, respectively.
• Figure 4: Quasi-periodic dynamics of the Helmet streamer: The temperature map from the quasi-equilibrium state of the Helmet streamer is shown in panel (a). An arrow is located at $r=16$ R$_\odot$ to show the location for synthetic in-situ measurements, discussed in Section \ref{['sec:in-situ']}. Panels (b)--(d) represent different phases of streamer dynamics after introducing the shear in the azimuthal $(\phi)$ direction.
• Figure 5: Dynamics in the vicinity of the pseudostreamer, revealing the presence of Interchange Magnetic Reconnection (IMR). The radial component of the magnetic field is represented by the colour map and the magnetic field lines are traced from random seed points. Similar to Fig \ref{['fig:dhelmet']}, the quasi-equilibrium state is shown in panel (a) and panels (b)--(d) refer to different times during the time period in which the shear is applied. An arrow is located at $r=2.5$ R$_\odot$ for a reference to compute synthetic in-situ observables (see Section \ref{['sec:in-situ']}).