Date of Award

Fall 2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Applied Physics - (Ph.D.)

Department

Physics

First Advisor

Chang Liu

Second Advisor

Haimin Wang

Third Advisor

Dale E. Gary

Fourth Advisor

Martin Schaden

Fifth Advisor

Peter William Schuck

Abstract

The rapid, irreversible change of the photospheric magnetic field has been recognized as an important element of the solar flare process. Recent theoretical work has shown that such a change would imply Lorentz force perturbations acting on both the outer solar atmosphere and the solar surface. This research uses vector magnetograms obtained with the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory to study a number of flares, which range from GOES-class C4 to X5 and occur in four active regions. In all the events, a permanent and rapid change of photospheric magnetic field closely associated with the flare occurrence is found. The change is predominantly in the form of an enhancement of the horizontal magnetic field, which is located around the magnetic polarity inversion line between flare ribbons. The area integral of the field change and the derived Lorentz force change both show a strong correlation with flare magnitude. For seven events associated with coronal mass ejections (CMEs), the CME mass is estimated using the observed CME velocity and the impulse provided by the upward Lorentz force. Furthermore, the flow field vorticity of selected sunspots away from flare kernels in the AR 11158 is calculated using the Differential Affine Velocity Estimator. It is found that some spots exhibit a sharp acceleration of rotation co-temporal with the rapid rising of the soft X-ray flux, and that such rotational disturbance may be driven by the Lorentz-force change in the horizontal direction.

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