Chromospheric signatures of small-scale flux emergence as observed with NST and Hinode instruments

TL;DR

This study investigates small-scale magnetic flux emergence and its chromospheric signatures using high-resolution solar observations, revealing that even tiny dipoles can influence the chromosphere and that flux disappearance may involve reconnection with large-scale fields.

Contribution

It provides detailed observational evidence of small-scale flux emergence and clarifies the mechanisms of flux disappearance and chromospheric activity using combined NST and Hinode data.

Findings

Small dipoles can reach the chromosphere and trigger activity.

Flux disappearance may involve reconnection with large-scale fields.

Hα bright points are co-spatial with Ca II H and G-band bright points.

Abstract

With the ever increasing influx of high resolution images of the solar surface obtained at a multitude of wavelengths, various processes occurring at small spatial scales have become a greater focus of our attention. Complex small-scale magnetic fields have been reported that appear to have enough stored to heat the chromosphere. While significant progress has been made in understanding small-scale phenomena, many specifics remain elusive. We present here a detailed study of a single event of disappearance of a magnetic dipole and associated chromospheric activity. Based on New Solar Telescope H$\alpha$ data and {\it Hinode} photospheric line-of-sight magnetograms and Ca II H images we report the following. 1) Our analysis indicates that even very small dipoles (elements separated by about 0\arcsec.5 or less) may reach the chromosphere and trigger non-negligible chromospheric activity. 2) Careful consideration of the magnetic environment where the new flux is deposited may shed light on the details of magnetic flux removal from the solar surface. We argue that the apparent collision and disappearance of two opposite polarity elements may not necessarily indicate their cancellation (i.e., reconnection, emergence of a "U" tube or submergence of $ \Omega $ loops). In our case, the magnetic dipole disappeared by reconnecting with overlying large-scale inclined plage fields. 3) Bright points seen in off-band H$\alpha$ images are very well-correlated with the Ca II H bright points, which in turn are co-spatial with G-band bright points. We further speculate that, in general, H$\alpha$ bright points are expected be co-spatial with photospheric BPs, however, a direct comparison is needed to refine their relationship.