Fast Prograde Coronal Flows in Solar Active Regions

TL;DR

This paper reports the discovery of persistent high-speed prograde horizontal flows in solar active regions, observed via extreme ultraviolet spectroscopy, consistent across solar cycles and independent of active-region latitude.

Contribution

It provides the first characterization of high-speed prograde flows in active regions using Sun-as-a-star spectroscopy, revealing their persistence and independence from solar cycle variations.

Findings

High-speed (>100 km/s) flows are observed in active regions.

Flows are prograde, evidenced by blueshifts and redshifts.

Flow behavior is consistent across solar cycles 24 and 25.

Abstract

We report the discovery and characterization of high-speed (>100 km/s) horizontal flows in solar active regions, making use of the Sun-as-a-star spectroscopy in the range 5-105 nm provided by the EVE (Extreme Ultraviolet Variability Experiment) spectrometers on the Solar Dynamics Observatory. These apparent flows are persistent on time scales of days, and are well observed in lines of Mg X, Si XII and Fe XVI for example. They are prograde, as evidenced directly by blueshifts/redshifts peaking at the east/west limb passages of isolated active regions. The high-speed flow behavior does not depend upon active-region latitude or solar cycle, with similar behavior in Cycles 24 and 25.