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) |
Persistent link: | http://urn.fi/urn:nbn:fi-fe201903057228 |
Language: | English |
Published: |
American Geophysical Union,
2017
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Publish Date: | 2019-03-05 |
Description: |
AbstractWe 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. see all
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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 |
OADOI: | https://oadoi.org/10.1002/2017JA024385 |
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 (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. |
https://creativecommons.org/licenses/by-nc-nd/4.0/ |