Solar cycle properties and surface-field reconstruction from sunspot observations by Schwabe
Final Report Abstract
The aim of the project was the investigation of historical sunspot data recorded by Samuel Heinrich Schwabe in 1825-1867, and the embedment in long-term series of sunspot group properties and magnetic reconstructions of the solar surface. The observations provided a total of 135,921 individual sunspot positions. The areas of the sunspots were derived from somewhat arbitrary size estimates through a statistical comparison with modern sunspot data. We obtained for most of the Schwabe spots areas in millionths of the solar hemisphere (MSH). We also grouped the individual sunspots into sunspot groups to the best of our knowledge. For the groups with more than one sunspot, we separated the spots into two polarities, with some uncertainty since we lack the information on the actual magnetic polarity of the individual spots. The polarities allowed us to compute the tilt angles of the groups against the solar equator. A dataset of 23,141 tilt angles was finally published. Cycle-averaged tilt angles were slightly lower than in the second half of the 20th century, but not significantly. We also analysed and added other historical data sources to the set of cycle-averaged tilt angles. We found that tilt angles before the Maunder minimum were as high as modern values. However, in the period after the Maunder minimum, tilt angles were lower, as indicated by two independent observers. These facts constrain the dynamo process leading to long-term variability of the solar cycle in that the tilt angle may not be the major driver for grand minima. Having sunspot positions and areas at hand, we started a reconstruction of the surface magnetic field using the surface flux transport model developed at Max Planck Institute for Solar System Research. The sunspot group information is converted into a radial field injection to the simulation and results in a magnetic butterfly diagram showing reversals of the polar magnetic field roughly at cycle maximum.
Publications
- Sunspot areas and tilt angles for solar cycles 7–10. Astron. Astrophys. 584 (2015), A73
Senthamizh Pavai, V., Arlt, R., Dasi-Espuig, M., Krivova, N. A., Solanki, S. K.
(See online at https://doi.org/10.1051/0004-6361/201527080) - Sunspot group tilt angle measurements from historical observations. Adv. Space Res. 58 (2016), 1468
Senthamizh Pavai, V., Arlt, R., Diercke, A., Denker, C., Vaquero, J. M.
(See online at https://doi.org/10.1016/j.asr.2016.03.002) - Sunspot positions, areas, and group tilt angles for 1611–1631 from observations by Christoph Scheiner. Astron. Astrophys. 595 (2016), A104
Arlt, R., Senthamizh Pavai, V., Schmiel, C., Spada, F.
(See online at https://doi.org/10.1051/0004-6361/201629000) - Wings of the butterfly: Sunspot groups for 1826–2015. Astron. Astrophys. 599 (2017), A131
Leussu, R., Usoskin, I. G., Senthamizh Pavai, V., Diercke, A., Arlt, R., Denker, C., Mursula, K.
(See online at https://doi.org/10.1051/0004-6361/201629533)
