University of Oulu

Tlatova, K., Tlatov, A., Pevtsov, A. et al. Sol Phys (2018) 293: 118.

Tilt of sunspot bipoles in Solar Cycles 15 to 24

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Author: Tlatova, Ksenia1; Tlatov, Andrey2,3; Pevtsov, Alexei4,5;
Organizations: 1St. Petersburg State University
2Kislovodsk Mountain Astronomical Station of Pulkovo Observatory
3Kalmyk State University
4National Solar Observatory, Boulder, USA
5ReSoLVE Centre of Excellence, Space Climate Research Unit, University of Oulu
6Astronomical Institute AS RUz
Format: article
Version: accepted version
Access: embargoed
Persistent link:
Language: English
Published: Springer Nature, 2018
Publish Date: 2019-08-08


We use recently digitized sunspot drawings from Mount Wilson Observatory to investigate the latitudinal dependence of tilt angles of active regions and its change with solar cycle. The drawings cover the period from 1917 to present and contain information as regards polarity and strength of magnetic field in sunspots. We identified clusters of sunspots of same polarity, and used these clusters to form “bipole pairs”. The orientation of these bipole pairs was used to measure their tilts. We find that the latitudinal profile of tilts does not monotonically increase with latitude as most previous studies assumed, but instead, it shows a clear maximum at about 25 – 30 degree latitudes. Functional dependence of tilt (γ) on latitude (φ) was found to be γ=(0.20±0.08)sin(2.80φ)+(−0.00±0.06). We also find that latitudinal dependence of tilts varies from one solar cycle to another, but larger tilts do not seem to result in stronger solar cycles. Finally, we find the presence of a systematic offset in tilt of active regions (non-zero tilts at the equator), with odd cycles exhibiting negative offset and even cycles showing the positive offset.

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Series: Solar physics
ISSN: 0038-0938
ISSN-E: 1573-093X
ISSN-L: 0038-0938
Volume: 293
Issue: 8
Article number: 118
DOI: 10.1007/s11207-018-1337-y
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: Work of individual co-authors was supported by their national grants and projects: the Academy of Finland to the ReSoLVE Centre of Excellence (project no. 272157), the Russian Foundation for Basic Research (RFBR, project 18-02-00098), the Russian Science Foundation (RSF, project 15-12-20001), and NASA’s grant NNX15AE95G. The authors are members of international team on Reconstructing Solar and Heliospheric Magnetic Field Evolution Over the Past Century supported by the International Space Science Institute (ISSI), Bern, Switzerland. The National Solar Observatory (NSO) is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under cooperative agreement with the National Science Foundation.
Academy of Finland Grant Number: 272157
Detailed Information: 272157 (Academy of Finland Funding decision)
Copyright information: © Springer Nature B.V. 2018. This is a post-peer-review, pre-copyedit version of an article published in Solar Physics. The final authenticated version is available online at: