University of Oulu

Hynönen R, Tanskanen EI & Francia P 2020. Solar cycle evolution of ULF wave power in solar wind and on ground. J.Space Weather Space Clim. 10, 43.

Solar cycle evolution of ULF wave power in solar wind and on ground

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Author: Hynönen, Reko1; Tanskanen, Eija I.1,2; Francia, Patrizia3
Organizations: 1Department of Electronics and Nanoengineering, Aalto University of Technology, 00076 Aalto, Finland
2Sodankylä Geophysical Observatory, University of Oulu, 99600 Sodankylä, Finland
3Dipartimento di Scienze Fisiche e Chimiche, Università dell’Aquila, Via Vetoio, Coppito, 67100 L’Aquila, Italy
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.1 MB)
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Language: English
Published: EDP Sciences, 2020
Publish Date: 2021-01-29


The solar cycle evolution of the ultra-low frequency (ULF) power was studied in solar wind and on ground. We aim finding out how the ULF power in interplanetary and on ground magnetic field evolves over the solar cycle 23 (SC23) and how well do they follow each other in monthly time scales. The hourly power of the ULF waves was computed in the Pc5 frequency range 2–7 mHz for years 1998–2008. The highest wave power in SC23 is found to occur in late 2003 and the lowest at the solar minimum. Ground ULF power follows the IMF power and solar wind speed, particularly well during declining phase. The ULF power in winter exceeds the ULF power in other seasons during the declining phase of SC23, while equinoxes dominate in the ascending phase and the solar maximum. The ground ULF power was found to rise with magnetic latitude from 54° to 73°, after which Pc5 power decreases towards the polar cap. The Pc5 power in the auroral zone is larger in the nightside than the dayside due to substorm activity implying that magnetotail processes are an important contributor to the nightside ULF power.

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Series: Journal of space weather and space climate
ISSN: 2115-7251
ISSN-E: 2115-7251
ISSN-L: 2115-7251
Volume: 10
Article number: 43
DOI: 10.1051/swsc/2020046
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This work was supported by ReSoLVE Centre of Excellence of the Academy of Finland (projects 272157 and 307411) and COST Action ES-1005 (TOSCA) and G-EPOS infrastructure within EPOS and FIN-EPOS (number 293488 and 311714).
Academy of Finland Grant Number: 272157
Detailed Information: 272157 (Academy of Finland Funding decision)
307411 (Academy of Finland Funding decision)
Copyright information: © R. Hynönen et al., Published by EDP Sciences 2020. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.