# The Chromospheric Response to the Sunquake generated by the X9.3 Flare of NOAA 12673

## TL;DR

This study presents the first evidence of chromospheric responses to sunquakes caused by a major solar flare, using multi-instrument observations to analyze velocity and asymmetry changes in the chromosphere.

## Contribution

It provides the first detailed analysis of chromospheric signatures associated with flare-induced sunquakes, combining HMI and SST data with advanced inversion techniques.

## Key findings

- Chromospheric crests show strong blue asymmetry.
- Velocities of chromospheric response range from 4.5 to 29.5 km/s.
- Upflows are responsible for the observed crests.

## Abstract

Active region NOAA 12673 was extremely volatile in 2017 September, producing many solar flares, including the largest of solar cycle 24, an X9.3 flare of 06 September 2017. It has been reported that this flare produced a number of sunquakes along the flare ribbon (Sharykin & Kosovichev 2018; Zhao & Chen 2018). We have used co-temporal and co-spatial Helioseismic and Magnetic Imager (HMI) line-of-sight (LOS) and Swedish 1-m Solar Telescope observations to show evidence of the chromospheric response to these sunquakes. Analysis of the Ca II 8542 \AA\space line profiles of the wavefronts revealed that the crests produced a strong blue asymmetry, whereas the troughs produced at most a very slight red asymmetry. We used the combined HMI, SST datasets to create time-distance diagrams and derive the apparent transverse velocity and acceleration of the response. These velocities ranged from 4.5 km s$^{-1}$ to 29.5 km s$^{-1}$ with a constant acceleration of 8.6 x 10$^{-3}$ km s$^{-2}$. We employed NICOLE inversions, in addition to the Center-of-Gravity (COG) method to derive LOS velocities ranging 2.4 km s$^{-1}$ to 3.2 km s$^{-1}$. Both techniques show that the crests are created by upflows. We believe that this is the first chromospheric signature of a flare induced sunquake.