Standing shocks in the inner slow solar wind

TL;DR

This paper investigates the formation of standing shocks in the inner slow solar wind caused by specific flow tube geometries near streamer helmets, using a simplified isothermal wind model.

Contribution

It demonstrates that standing shocks can form in the inner slow solar wind due to streamer geometry, expanding understanding of solar wind dynamics.

Findings

Standing shocks exist in a broad parameter space.

Shocks can occur with temperatures just above 1 MK.

Streamers with cusps beyond 3.2 R_s can support shock solutions.

Abstract

The slow solar wind, or at least a significant part of it, originates from the region bordering streamer helmets, where the flow tube geometry is distinct from flow tubes rooted in the center of coronal holes. We examine whether this particular tube geometry leads to standing shocks in the inner slow wind in this region. To isolate the influence of tube geometry, a simple isothermal wind model is employed and is solved in terms of the Lambert W function. In addition to a continuous solution, the model may also admit solutions with shocks, readily constructed with a graphical approach. When allowed, the shock solutions appear in pairs, one with a shock located in the streamer stalk, the other with a shock below the cusp along the streamer border. We show that solutions with standing shocks exist in a broad area in the parameter space characterizing the wind temperature and flow tube. In particular, streamers with cusps located at a heliocentric distance $\gtrsim 3.2 R_\odot$ can readily support discontinuous slow winds with temperatures barely higher than 1 MK.