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Exploring the Physical Relationship Among Photospheric Magnetic Field Changes, Sunspot Motions, and Sunquakes During Solar Eruptions

Chang Liu/New Jersey Institute of Technology

Solar flares and coronal mass ejections (CMEs) are generally believed to be manifestations of a sudden and rapid release of the accumulated magnetic energy in the corona. The transients created in the tenuous low-beta corona are generally thought unlikely to alter the photospheric magnetic fields, which are line-tied to the dense high-beta photosphere. Only recently, a rapid back reaction on the photosphere due to the coronal magnetic field reconfiguration has been seriously considered from the theoretical point of view (e.g., Hudson et al. 2008; Fisher et al. 2012), with a prediction that the photospheric magnetic field would be oriented more horizontally resulting in a Lorentz force acting on the solar surface and interior. Such magnetic impulse is speculated to cause sudden perturbation of sunspots and excitation of seismic waves. Thus the changes in the photospheric field and dynamics associated with flares/CMEs could serve as a direct observational probe of the energy transformations and momentum balance in the flare/CME process. Notably, a more inclined state of the photospheric magnetic field persisting after flares than before has been consistently found by our group in the past two decades. The studies so far are, nevertheless, still very limitedmainly due to the quality and availability of ground-based vector magnetograms. The solar maximum 24 is approaching, and it is now possible to obtain the unprecedented high-quality and high-resolution vector magnetograms, line-of-sight Doppler images, and continuum and line intensity images of flaring active regions from the Solar Dynamics Observatory (SDO) and Hinode. These make it an opportune and timely moment to quantitatively address the physics behind the flare-related photospheric (and interior) phenomena including magnetic field changes, sunspot motions, and sunquakes. The scientific objectives of this study include three related components: 1. Using vector magnetograms fromSDO/HMI and Hinode supplemented by the archived and future data from BBSO, we will systematically study the temporal and spatial relationship between the changes of vectormagnetic fields and the related dynamics including signatures of flare energy release, the CME launch, and variation of sunspot white-light (especially penumbra) structure. We will explore the connection of the properties of the Lorentz-force change with the flare magnitude and CME energetics. 2. We will trace the sunspot motions throughout the eruption process, and study the correlation between it and the horizontal component of the Lorentz-force change, in the directions both parallel and perpendicular to the flaring magnetic polarity inversion line. As related, the evolution of the sunspot rotational motion across the flare time will be characterized based on the flow field derived using the differential affine velocity estimator for vector magnetograms (DAVE4VM). 3. Applying helioseismic techniques to the LOS velocity data cube, we will reveal the seismic transients due to the flare impact. We will then mainly concern ourselves with the question of whether the photospheric vector magnetic field changes and sunspot motions could be physically associated with sunquakes. The anisotropy of sunquake ripples will also be explored under this context. The proposed research directly responds to the focused science topic ¡°Flare Dynamics in the Lower Solar Atmosphere¡±. We will contribute to the focused team effort by analyzing high- quality vector magnetograms, velocity and intensity images, and multiwavelength (e.g., hard X-rays and white light) flare/CME data obtained with the state-of-the-art NASA missions (SDO, Hinode, and RHESSI). This will help to address the fundamental physics concerning the transport of energy and momentum into the interior from the solar atmosphere during flares/ CMEs. Our team has profound expertise in the related data analysis as demonstrated in many publications.