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

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 2017 September 06. It has been reported that this flare produced a number of sunquakes along the flare ribbon. We have used cotemporal and cospatial Helioseismic and Magnetic Imager (HMI) line of sight (LOS) and Swedish 1 m Solar Telescope (SST) observations to show evidence of the chromospheric response to these sunquakes. Analysis of the Ca ii 8542 Å 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 data sets to create time–distance diagrams and derive the apparent transverse velocity and acceleration of the response. These velocities ranged from 4.5 to 29.5 km s −1 with a constant acceleration of 8.6 × 10 −3 km s −2 . We employed NICOLE inversions, in addition to the center-of-gravity method to derive LOS velocities ranging from 2.4 km s −1 –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.