The Formation and Lifetime of Outflows in a Solar Active Region

TL;DR

This study investigates the formation and duration of upflows in a solar active region, revealing they form rapidly low in the atmosphere and persist throughout the active region’s lifetime, contributing to the solar wind.

Contribution

It provides new insights into the timing, formation mechanism, and longevity of active region upflows, linking them to small eruptions and radio noise storms.

Findings

Upflows form quickly low in the atmosphere.

Upflows are associated with small eruptions and radio noise storms.

Upflows persist during most of the active region's lifetime.

Abstract

Active regions are thought to be one contributor to the slow solar wind. Upflows in EUV coronal spectral lines are routinely osberved at their boundaries, and provide the most direct way for upflowing material to escape into the heliosphere. The mechanisms that form and drive these upflows, however, remain to be fully characterised. It is unclear how quickly they form, or how long they exist during their lifetimes. They could be initiated low in the atmosphere during magnetic flux emergence, or as a response to processes occuring high in the corona when the active region is fully developed. On 2019, March 31, a simple bipolar active region (AR 12737) emerged and upflows developed on each side. We used observations from Hinode, SDO, IRIS, and Parker Solar Probe (PSP) to investigate the formation and development of the upflows from the eastern side. We used the spectroscopic data to detect the upflow, and then used the imaging data to try to trace its signature back to earlier in the active region emergence phase. We find that the upflow forms quickly, low down in the atmosphere, and that its initiation appears associated with a small field-opening eruption and the onset of a radio noise storm detected by PSP. We also confirmed that the upflows existed for the vast majority of the time the active region was observed. These results suggest that the contribution to the solar wind occurs even when the region is small, and continues for most of its lifetime.