Two-Dimensional Spectroscopy of Photospheric Shear Flows in a Small delta Spot

TL;DR

This study uses high-resolution solar observations to analyze shear flows in a complex sunspot group, revealing their commonality and independence from magnetic shear changes, thus refining understanding of flare-related magnetic activity.

Contribution

It extends previous shear flow studies to quieter active regions, demonstrating their prevalence and independence from magnetic shear changes in delta spots.

Findings

Shear flows are common in complex active regions and delta spots.

Shear flows are not necessarily linked to magnetic shear changes.

High-resolution observations captured detailed flow evolution over an hour.

Abstract

In recent high-resolution observations of complex active regions, long-lasting and well-defined regions of strong flows were identified in major flares and associated with bright kernels of visible, near-infrared, and X-ray radiation. These flows, which occurred in the proximity of the magnetic neutral line, significantly contributed to the generation of magnetic shear. Signatures of these shear flows are strongly curved penumbral filaments, which are almost tangential to sunspot umbrae rather than exhibiting the typical radial filamentary structure. Solar active region NOAA 10756 was a moderately complex, beta-delta sunspot group, which provided an opportunity to extend previous studies of such shear flows to quieter settings. We conclude that shear flows are a common phenomenon in complex active regions and delta spots. However, they are not necessarily a prerequisite condition for flaring. Indeed, in the present observations, the photospheric shear flows along the magnetic neutral line are not related to any change of the local magnetic shear. We present high-resolution observations of NOAA 10756 obtained with the 65-cm vacuum reflector at Big Bear Solar Observatory (BBSO). Time series of speckle-reconstructed white-light images and two-dimensional spectroscopic data were combined to study the temporal evolution of the three-dimensional vector flow field in the beta-delta sunspot group. An hour-long data set of consistent high quality was obtained, which had a cadence of better than 30 seconds and sub-arcsecond spatial resolution.