The Formation of Heliospheric Arcs of Slow Solar Wind

TL;DR

This paper uses advanced simulations to explain how localized solar regions produce large-scale slow solar wind structures, revealing the formation of heliospheric arcs far from the heliospheric current sheet.

Contribution

It demonstrates that small-scale magnetic features at the Sun can generate large-scale slow solar wind arcs through dynamic processes.

Findings

Giant arcs of closed-field plasma form far from the HCS.

Simulations show the role of supergranule-like flows in arc formation.

Results match observed slow solar wind structures.

Abstract

A major challenge in solar and heliospheric physics is understanding how highly localized regions, far smaller than 1 degree at the Sun, are the source of solar-wind structures spanning more than 20 degrees near Earth. The Sun's atmosphere is divided into magnetically open regions, coronal holes, where solar-wind plasma streams out freely and fills the solar system, and closed regions, where the plasma is confined to coronal loops. The boundary between these regions extends outward as the heliospheric current sheet (HCS). Measurements of plasma composition imply that the solar wind near the HCS, the so-called slow solar wind, originates in closed regions, presumably by the processes of field-line opening or interchange reconnection. Mysteriously, however, slow wind is also often seen far from the HCS. We use high-resolution, three-dimensional magnetohydrodynamic simulations to calculate the dynamics of a coronal hole whose geometry includes a narrow corridor flanked by closed field and which is driven by supergranule-like flows at the coronal-hole boundary. We find that these dynamics result in the formation of giant arcs of closed-field plasma that extend far from the HCS and span tens of degrees in latitude and longitude at Earth, accounting for the slow solar wind observations.