University of Oulu

Alexei A. Pevtsov, Kseniya A. Tlatova, Alexander A. Pevtsov, Elina Heikkinen, Ilpo Virtanen, Nina V. Karachik, Luca Bertello, Andrey G. Tlatov, Roger Ulrich and Kalevi Mursula, Reconstructing solar magnetic fields from historical observations - V. Sunspot magnetic field measurements at Mount Wilson Observatory, A&A, 628 (2019) A103, DOI:

Reconstructing solar magnetic fields from historical observations : V. Sunspot magnetic field measurements at Mount Wilson Observatory

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Author: Pevtsov, Alexei A.1,2; Tlatova, Kseniya A.3; Pevtsov, Alexander A.1;
Organizations: 1National Solar Observatory, Boulder, CO 80303, USA
2ReSoLVE Centre of Excellence, Astronomy and Space Physics Research Unit, University of Oulu, PO Box 3000, 90014 Oulu, Finland
3Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo, 196140 Saint Petersburg, Russia
4Uzbekistan Academy of Sciences, Ulugh Beg Astronomical Institute, Tashkent, Uzbekistan
5Kislovodsk Mountain Astronomical Station of Pulkovo Observatory, Kislovodsk, Russia
6Kalmyk State University, Elista, Russia
7University of California at Los Angeles (UCLA), Los Angeles, CA, USA
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 3 MB)
Persistent link:
Language: English
Published: EDP Sciences, 2019
Publish Date: 2019-09-24


Context: Systematic observations of magnetic field strength and polarity in sunspots began at Mount Wilson Observatory (MWO), USA in early 1917. Except for a few brief interruptions, this historical dataset has continued until the present.

Aims: Sunspot field strength and polarity observations are critical in our project of reconstructing the solar magnetic field over the last hundred years. We provide a detailed description of the newly digitized dataset of drawings of sunspot magnetic field observations.

Methods: The digitization of MWO drawings is based on a software package that we developed. It includes a semiautomatic selection of solar limbs and other features of the drawing, and a manual entry of the time of observations, measured field strength, and other notes handwritten on each drawing. The data are preserved in an MySQL database.

Results: We provide a brief history of the project and describe the results from digitizing this historical dataset. We also provide a summary of the final dataset and describe its known limitations. Finally, we compare the sunspot magnetic field measurements with those from other instruments, and demonstrate that, if needed, the dataset could be continued using modern observations such as, for example, the Vector Stokes Magnetograph on the Synoptic Optical Long-term Investigations of the Sun platform.

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Series: Astronomy and astrophysics
ISSN: 0004-6361
ISSN-E: 1432-0746
ISSN-L: 0004-6361
Volume: 628
Article number: A103
DOI: 10.1051/0004-6361/201834985
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: We acknowledge the financial support by the Academy of Finland to the ReSoLVE Centre of Excellence (project no. 307411). Also acknowledged is the funding from the Russian Foundation for Basic Research (RFBR, project 18-02-00098) and the Russian Science Foundation (RSF, project 15-12-20001). US contribution to this project was partially supported by NASA NNX15AE95G grant
Academy of Finland Grant Number: 307411
Detailed Information: 307411 (Academy of Finland Funding decision)
Copyright information: © ESO 2019.