University of Oulu

Tanskanen, E. I., Snekvik, K., Slavin, J. A., Pérez‐Suárez, D., Viljanen, A., Goldstein, M. L., … Mursula, K. (2017). Solar cycle occurrence of Alfvénic fluctuations and related geo‐efficiency. Journal of Geophysical Research: Space Physics, 122, 9848–9857.

Solar cycle occurrence of Alfvénic fluctuations and related geo‐efficiency

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Author: Tanskanen, E. I.1; Snekvik, K.2; Slavin, J. A.3;
Organizations: 1ReSoLVE Centre of Excellence, Aalto University, Espoo, Finland
2Birkeland Centre for Space Sciences, University of Bergen, Bergen, Norway
3Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA
4University College London, UK
5Finnish Meteorological Institute, Helsinki, Finland
6Space Science Institute, Boulder, CO, USA
7Max Planck Institute for Solar System Research, Göttingen, Germany
8Space Climate Research Unit, ReSoLVE Centre of Excellence, Oulu University, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.6 MB)
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Language: English
Published: American Geophysical Union, 2017
Publish Date: 2019-03-05


We examine solar wind intervals with Alfvénic fluctuations (ALFs) in 1995–2011. The annual number, the total annual duration, and the average length of ALFs vary over the solar cycle, having a maximum in 2003 and a minimum in 2009. ALFs are most frequent in the declining phase of solar cycle, when the number of high‐speed streams at the Earth’s vicinity is increased. There is a rapid transition after the maximum of solar cycle 23 from ALFs being mainly embedded in slow solar wind (<400 km/s) until 2002 to ALFs being dominantly in fast solar wind (>600 km/s) since 2003. Cross helicity increased by 30% from 2002 to 2003 and maximized typically 4–6 h before solar wind speed maximum. Cross helicity remained elevated for several days for highly Alfvénic non‐ICME streams, but only for a few hours for ICMEs. The number of substorms increased by about 40% from 2002 to 2003, and the annual number of substorms closely follows the annual cross helicity. This further emphasizes the role of Alfvénic fluctuations in modulating substorm activity. The predictability of substorm frequency and size would be greatly improved by monitoring solar wind Alfvénic fluctuations in addition to the mean values of the important solar wind parameters.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 122
Issue: 10
Pages: 9848 - 9857
DOI: 10.1002/2017JA024385
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 272157) and by the European Community's Seventh Framework Program under grants 313038/STORM and 283676/ESPAS. M.K. acknowledges funding from the “Active Suns” research project of Helsinki University.
EU Grant Number: (313038) STORM - Solar system plasma Turbulence: Observations, inteRmittency and Multifractals
(283676) ESPAS - Near-Earth Space Data Infrastructure for e-Science
Academy of Finland Grant Number: 272157
Detailed Information: 272157 (Academy of Finland Funding decision)
Copyright information: © 2017. The Authors.This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.