SH43B-2442
Sunspot Tilt Angles Measured with MDI/SOHO and HMI/SDO
Thursday, 17 December 2015
Poster Hall (Moscone South)
Jing Li, University of California Los Angeles, Los Angeles, CA, United States and Roger K Ulrich, American Astronomical Society, Chevy Chase, MD, United States
Abstract:
We present sunspot magnetic tilt angles measured from 1996 to the present time, spanning almost two solar cycles. Full disk magnetograms from MDI/SoHO and HMI/SDO are used in our study. The data cadence in our analyses is 96 minutes per day giving about 90 measurements of the tilt angles for each sunspot during the disk passage between -40 to +40 longitudinal degree. In addition to an automated computation, we use a scheme to visually examine each sunspot efficiently to check the tilt angle determinations. Such measurements not only confirm Joy’s and Hale’s laws, but also reveal the tilt angle variations during the sunspot lifetime, the effect of Coriolis force on the magnetic flux tubes, and the tilt angle dependence of the cycle progress. The measurements also provide uncertainties on the tilt angle measurements.
