University of Oulu

Hamada, A., Asikainen, T., Virtanen, I. et al. Sol Phys (2018) 293: 71. https://doi.org/10.1007/s11207-018-1289-2

Automated identification of coronal holes from synoptic EUV maps

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Author: Hamada, Amr1; Asikainen, Timo1; Virtanen, Ilpo1;
Organizations: 1ReSoLVE Centre of Excellence, Space Climate Research Unit, University of Oulu, Oulu, Finland
Format: article
Version: accepted version
Access: open
Online Access: PDF Full Text (PDF, 5 MB)
Persistent link: http://urn.fi/urn:nbn:fi-fe2019100431189
Language: English
Published: Springer Nature, 2018
Publish Date: 2019-10-04
Description:

Abstract

Coronal holes (CHs) are regions of open magnetic field lines in the solar corona and the source of the fast solar wind. Understanding the evolution of coronal holes is critical for solar magnetism as well as for accurate space weather forecasts. We study the extreme ultraviolet (EUV) synoptic maps at three wavelengths (195 Å/193 Å, 171 Å and 304 Å) measured by the Solar and Heliospheric Observatory/Extreme Ultraviolet Imaging Telescope (SOHO/EIT) and the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) instruments. The two datasets are first homogenized by scaling the SDO/AIA data to the SOHO/EIT level by means of histogram equalization. We then develop a novel automated method to identify CHs from these homogenized maps by determining the intensity threshold of CH regions separately for each synoptic map. This is done by identifying the best location and size of an image segment, which optimally contains portions of coronal holes and the surrounding quiet Sun allowing us to detect the momentary intensity threshold. Our method is thus able to adjust itself to the changing scale size of coronal holes and to temporally varying intensities. To make full use of the information in the three wavelengths we construct a composite CH distribution, which is more robust than distributions based on one wavelength. Using the composite CH dataset we discuss the temporal evolution of CHs during the Solar Cycles 23 and 24.

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Series: Solar physics
ISSN: 0038-0938
ISSN-E: 1573-093X
ISSN-L: 0038-0938
Volume: 293
Article number: 71
DOI: 10.1007/s11207-018-1289-2
OADOI: https://oadoi.org/10.1007/s11207-018-1289-2
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Subjects:
Funding: We acknowledge the financial support by the Academy of Finland to the ReSoLVE Centre of Excellence (projects 272157, 307411) as well as to project 257403.
Academy of Finland Grant Number: 272157
307411
257403
Detailed Information: 272157 (Academy of Finland Funding decision)
307411 (Academy of Finland Funding decision)
257403 (Academy of Finland Funding decision)
Copyright information: © Springer Science+Business Media B.V., part of Springer Nature 2018. This is a post-peer-review, pre-copyedit version of an article published in Sol Phys. The final authenticated version is available online at: https://doi.org/10.1007/s11207-018-1289-2