Horizontal flows concurrent with an X2.2 flare in active region NOAA 11158

TL;DR

This study analyzed horizontal flows in active region NOAA 11158 during an X2.2 solar flare, revealing weak shear flows, post-flare flow shifts, and small-scale magnetic features associated with white-light emission, highlighting subtle photospheric responses.

Contribution

It provides detailed measurements of photospheric flows and magnetic features during a major solar flare, emphasizing the subtlety of photospheric signatures compared to other flares.

Findings

Weak shear flows along the polarity inversion line

Post-flare shift of counter-streaming regions

Small-scale magnetic features with high flow speeds

Abstract

Horizontal proper motions were measured with local correlation tracking (LCT) techniques in active region NOAA 11158 on 2011 February 15 at a time when a major (X2.2) solar flare occurred. The measurements are based on continuum images and magnetograms of the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. The observed shear flows along the polarity inversion line were rather weak (a few 100 m/s). The counter-streaming region shifted toward the north after the flare. A small circular area with flow speeds of up to 1.2 km/s appeared after the flare near a region of rapid penumbral decay. The LCT signal in this region was provided by small-scale photospheric brigthenings, which were associated with fast traveling moving magnetic features. Umbral strengthening and rapid penumbral decay was observed after the flare. Both phenomena were closely tied to kernels of white-light flare emission. The white-light flare only lasted for about 15 min and peaked 4 min earlier than the X-ray flux. In comparison to other major flares, the X2.2 flare in active region NOAA 11158 only produced diminutive photospheric signatures.