The Dynamic Evolution of Solar Wind Streams Following Interchange Reconnection

TL;DR

This paper models the evolution of solar wind streams after interchange reconnection, revealing how initial discontinuities develop into shock and rarefaction waves, affecting plasma properties and ionization states in the heliosphere.

Contribution

It introduces a simulation of plasma dynamics and ionization in a newly-opened magnetic flux tube, providing insights into the effects of interchange reconnection on the slow solar wind.

Findings

Reconnection site discontinuity evolves into an N-wave structure.

Density, velocity, and ionization ratios are enhanced in the N-wave.

Ionization discontinuity propagates and arrives later than the wave.

Abstract

Interchange reconnection is thought to play an important role in determining the dynamics and material composition of the slow solar wind that originates from near coronal hole boundaries. To explore the implications of this process we simulate the dynamic evolution of a solar wind stream along a newly-opened magnetic flux tube. The initial condition is composed of a piecewise continuous dynamic equilibrium in which the regions above and below the reconnection site are extracted from steady-state solutions along open and closed field lines. The initial discontinuity at the reconnection site is highly unstable and evolves as a Riemann problem, decomposing into an outward-propagating shock and inward-propagating rarefaction that eventually develop into a classic N-wave configuration. This configuration ultimately propagates into the heliosphere as a coherent structure and the entire system eventually settles to a quasi-steady wind solution. In addition to simulating the fluid evolution we also calculate the time-dependent non-equilibrium ionization of oxygen in real time in order to construct in situ diagnostics of the conditions near the reconnection site. This idealized description of the plasma dynamics along a newly-opened magnetic field line provides a baseline for predicting and interpreting the implications of interchange reconnection for the slow solar wind. Notably, the density and velocity within the expanding N-wave are generally enhanced over the ambient wind, as is the O7+/O6+ ionization ratio, which exhibits a discontinuity across the reconnection site that is transported by the flow and arrives later than the propagating N-wave.