Seasonal solar wind speeds for the last 100 years : unique coronal hole structures during the peak and demise of the Grand Modern Maximum
Mursula, Kalevi; Holappa, Lauri; Lukianova, R. (2017-01-28)
URL:Journal: Geophysical Research Letters (ISSN: 0094-8276, ESSN: 1944-8007) RoMEO: This is a RoMEO green journal Paid OA: A paid open access option is available for this journal. Author's Pre-print: green tick author can archive pre-print (ie pre-refereeing) Author's Post-print: green tick author can archive post-print (ie final draft post-refereeing) Publisher's Version/PDF: grey tick subject to Restrictions below, author can archive publisher's version/PDF General Conditions: Authors' Pre-print on authors' personal website or departmental website Authors' Post-print on authors' personal website or departmental website Set statements to accompany submitted, accepted and published articles Publisher copyright and source must be acknowledged with DOI Publisher's version/PDF must be used in Institutional Repository 6 months after publication. Mandated OA: (Awaiting information) Paid Open Access: Open Access Notes: Publisher last reviewed on 01/07/2016 Copyright: Copyright Form (pdf) - Copyright Transfer and Open Access Information - Author Resources - Usage Permissions Updated: 01-Jul-2016 - Suggest an update for this record Link to this page: http://www.sherpa.ac.uk/romeo/issn/0094-8276/ Published by: American Geophysical Union (AGU) [Client Organisation] - Green Policies in RoMEO Other parties: Wiley [Commercial Publisher] - Yellow Policies in RoMEO Guidance: Please see the list of Publisher Categories in RoMEO for guidance on interpreting the priority of multiple publishers.
Mursula, K., L. Holappa, and R. Lukianova (2017), Seasonal solar wind speeds for the last 100 years: Unique coronal hole structures during the peak and demise of the Grand Modern Maximum, Geophys. Res. Lett., 44, 30–36, doi:10.1002/2016GL071573
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Solar coronal holes are sources of high-speed solar wind streams, which cause persistent geomagnetic activity especially at high latitudes. Here we estimate seasonal solar wind speeds at 1 AU for the last 100 years using high-latitude geomagnetic measurements and show that they give information on the long-term evolution of important structures of the solar large-scale magnetic ﬁeld, such as persistent coronal holes. We ﬁnd that the centennial evolution of solar wind speed at 1 AU is different for equinoxes and solstices, reﬂecting differences in the evolution of polar coronal hole extensions and isolated low-latitude coronal holes. Equinoctial solar wind speeds had their centennial maximum in 1952, during the declining phase of solar cycle 18, verifying that polar coronal holes had exceptionally persistent extensions just before the peak of the Grand Modern Maximum of solar activity. On the other hand, solstice speeds had their centennial maximum during the declining phase of solar cycle 23 due to large low-latitude coronal holes. A similar conﬁguration of seasonal speeds as in cycle 23 was not found earlier, not even during the less active cycles of early 20th century. Therefore, the exceptional occurrence of persistent, isolated low-latitude coronal holes in cycle 23 is not related to the absolute level of sunspot activity but, most likely, to the demise of the Grand Modern Maximum.
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