Atmospheric responses to flare generated sunquakes

Abstract

This thesis presents the results of the first detection of an atmospheric response to a flare induced Sunquake (SQ). Ground-based observations of the Ca II 8542 Å and H-α 6563 Å passbands from the Swedish 1-m Solar Telescope (SST) were used in combination with space-based observations from the Heliosesimic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). Both instruments observed wavefronts emanating from the X9.3 solar flare of 2017 September 06, from active region NOAA 12673. The photospheric SQ had already been reported by Sharykin & Kosovichev (2018). Temporal and spatial alignment of these data showed that the wavefronts in the photosphere were creating the wavefronts in the chromosphere. Combining the datasets to create a single dataset allowed a time-distance diagram to be created, which meant the apparent transverse velocities and accelerations of the SQ could be derived. The velocity of the wavefront ranged from 4.5 kms−1 to 29.5 kms−1 with a constant acceleration of 8.6 × 10−3 kms−2. Employing NICOLE inversions, in addition to the Center-of-Gravity method, allowed the line-of-sight velocities in the Ca II 8542 Å data to be derived, ranging from 2.4 kms−1 to 3.2 kms−1. Both techniques show that the wavefronts in the Ca II 8542 Å line were upflows. A second detection of a chromospheric response to a SQ was observed in the X2.2 flare of the same date, also observed in the Ca II 8542 Å passband from the SST, and it was found to also be created by an upflow of plasma. The SQ generated by the X9.3 flare of 2017 September 06 created a response in observations obtained with the Atmospheric Imaging Assembly (AIA) 1600 Å and 1700 Å passbands, in addition to the Ca II 8542 Å passband from the SST. Observations from these passbands for all flares from Solar Cycle 24 were analysed for the presence of SQ signatures. Using the comprehensive SQ list reported in Sharykin & Kosovichev (2020) as a start, it was found that 9 out of 62 SQ candidates produced a response clearly visible in both AIA passbands, after frequency filtering was applied to the data. The first signature of a response is detected at distances of 5.2 Mm to 25.7 Mm from the flare ribbon. Time-distance analysis was used to calculate apparent transverse velocities with maxima as high as 41 kms-1 in the ultraviolet data. This analysis showed that flare induced SQ signatures can be detected as high as the chromosphere using observations from the AIA 1600 Å and 1700 Å passbands. My investigation has not found any correlation between the GOES flare classification and the appearance of the SQ at chromospheric heights.

Date of Award	Dec 2021
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Michail Mathioudakis (Supervisor) & David Jess (Supervisor)