STEREO Observations of Quasi-Periodically Driven High Velocity Outflows in Polar Plumes

TL;DR

This study uses high-resolution STEREO EUV observations to analyze high-velocity, quasi-periodic plasma jets in polar plumes, revealing their potential role in supplying heated mass to the fast solar wind.

Contribution

It reinterprets polar plume dynamics by identifying high-speed upflows as jets rather than waves, based on improved imaging and diagnostics, linking them to solar wind acceleration.

Findings

Jets travel at ~135 km/s across temperatures 0.5-1.5 MK.

Jets repeat every 5 to 25 minutes with ~5% brightness enhancement.

Jets are multi-thermal and originate in the upper chromosphere.

Abstract

Plumes are one of the most ubiquitous features seen at the limb in polar coronal holes and are considered to be a source of high density plasma streams to the fast solar wind. We analyze STEREO observations of plumes and aim to reinterpret and place observations with previous generations of EUV imagers within a new context that was recently developed from Hinode observations. We exploit the higher signal-to-noise, spatial and temporal resolution of the EUVI telescopes over that of SOHO/EIT to study the temporal variation of polar plumes in high detail. We employ recently developed insight from imaging (and spectral) diagnostics of active region, plage, and quiet Sun plasmas to identify the presence of apparent motions as high-speed upflows in magnetic regions as opposed to previous interpretations of propagating waves. In almost all polar plumes observed at the limb in these STEREO sequences, in all coronal passbands, we observe high speed jets of plasma traveling along the structures with a mean velocity of 135km/s at a range of temperatures from 0.5-1.5MK. The jets have an apparent brightness enhancement of ~5% above that of the plumes they travel on and repeat quasi-periodically, with repeat-times ranging from five to twenty-five minutes. We also notice a very weak, fine scale, rapidly evolving, but ubiquitous companion of the plumes that covers the entire coronal hole limb. The observed jets are remarkably similar in intensity enhancement, periodicity and velocity to those observed in other magnetic regions of the solar atmosphere. They are multi-thermal in nature. We infer that the jets observed on the plumes are a source of heated mass to the fast solar wind. Further, based on the previous results that motivated this study, we suggest that these jets originated in the upper chromosphere.