Widespread Occurrence of High-Velocity Upflows in Solar Active Regions

TL;DR

This study systematically demonstrates that high-velocity upflows with asymmetric blue wings are a widespread and consistent feature at the boundaries of solar active regions, observed across multiple cases.

Contribution

It provides the first comprehensive analysis showing the ubiquity of high-speed upflows and blue wing asymmetries in solar active regions using Hinode/EIS data.

Findings

Upflows are present at both east and west boundaries of all active regions studied.

Average upflow velocities range from -5 to -26 km/s.

High speed blue wing asymmetries are observed in every line profile analyzed.

Abstract

We performed a systematic study of 12 active regions (ARs) with a broad range of areas, magnetic flux and associated solar activity in order to determine whether there are upflows present at the AR boundaries and if these upflows exist, whether there is a high speed asymmetric blue wing component present in the upflows. To identify the presence and locations of the AR upflows we derive relative Doppler velocity maps by fitting a Gaussian function to {\it Hinode}/EIS Fe XII 192.394\,\AA\ line profiles. To determine whether there is a high speed asymmetric component present in the AR upflows we fit a double Gaussian function to the Fe XII 192.394\,\AA\ mean spectrum that is computed in a region of interest situated in the AR upflows. Upflows are observed at both the east and west boundaries of all ARs in our sample with average upflow velocities ranging between -5 to -26~km s$^{-1}$. A blue wing asymmetry is present in every line profile. The intensity ratio between the minor high speed asymmetric Gaussian component compared to the main component is relatively small for the majority of regions however, in a minority of cases (8/30) the ratios are large and range between 20 to 56~\%. These results suggest that upflows and the high speed asymmetric blue wing component are a common feature of all ARs.