Flows at the Edge of an Active Region: Observation and Interpretation

TL;DR

This study investigates the nature of upflows at active region edges, analyzing their magnetic connectivity and contribution to the solar wind through observations and magnetic field modeling.

Contribution

It provides new insights into the magnetic connectivity of upflows and quantifies their contribution to the solar wind in active regions.

Findings

Upflows can be confined in magnetic loops or open field lines.

Approximately 18% of the mass flow from AR10942 reaches AR10943.

Magnetic connectivity explains the observed plasma flows.

Abstract

Upflows observed at the edges of active regions have been proposed as the source of the slow solar wind. In the particular case of Active Region (AR) 10942, where such an upflow has been already observed, we want to evaluate the part of this upflow that actually remains confined in the magnetic loops that connect AR10942 to AR10943. Both active regions were visible simultaneously on the solar disk and were observed by STEREO/SECCHI EUVI. Using Hinode/EIS spectra, we determine the Doppler shifts and densities in AR10943 and AR10942, in order to evaluate the mass flows. We also perform magnetic field extrapolations to assess the connectivity between AR10942 and AR10943. AR10943 displays a persistent downflow in Fe XII. Magnetic extrapolations including both ARs show that this downflow can be connected to the upflow in AR10942. We estimate that the mass flow received by AR10943 areas connected to AR10942 represents about 18% of the mass flow from AR10942. We conclude that the upflows observed on the edge of active regions represent either large-scale loops with mass flowing along them (accounting for about one-fifth of the total mass flow in this example) or open magnetic field structures where the slow solar wind originates.