University of Oulu

Lukianova, R., L. Holappa, and K. Mursula (2017), Centennial evolution of monthly solar wind speeds: Fastest monthly solar wind speeds from long‐duration coronal holes, J. Geophys. Res. Space Physics, 122, 2740–2747, doi:10.1002/2016JA023683

Centennial evolution of monthly solar wind speeds : fastest monthly solar wind speeds from long‐duration coronal holes

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Author: Lukianova, Renata1,2,3; Holappa, Lauri1; Mursula, Kalevi1
Organizations: 1ReSoLVE Centre of Excellence, Space Climate Research Unit, University of Oulu, Oulu, Finland
2Geophysical Center of Russian Academy of Science, Moscow, Russia
3Space Research Institute, Moscow, Russia
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.9 MB)
Persistent link: http://urn.fi/urn:nbn:fi-fe201903057167
Language: English
Published: American Geophysical Union, 2017
Publish Date: 2019-03-05
Description:

Abstract

High‐speed solar wind streams (HSSs) are very efficient drivers of geomagnetic activity at high latitudes. In this paper we use a recently developed ΔH parameter of geomagnetic activity, calculated from the nightside hourly magnetic field measurements of the Sodankylä observatory, as a proxy for solar wind (SW) speed at monthly time resolution in 1914–2014 (solar cycles 15–24). The seasonal variation in the relation between monthly ΔH and solar wind speed is taken into account by calculating separate regressions between ΔH and SW speed for each month. Thereby, we obtain a homogeneous series of proxy values for monthly solar wind speed for the last 100 years. We find that the strongest HSS‐active months of each solar cycle occur in the declining phase, in years 1919, 1930, 1941, 1952, 1959, 1973, 1982, 1994, and 2003. Practically all these years are the same or adjacent to the years of annual maximum solar wind speeds. This implies that the most persistent coronal holes, lasting for several solar rotations and leading to the highest annual SW speeds, are also the sources of the highest monthly SW speeds. Accordingly, during the last 100 years, there were no coronal holes of short duration (of about one solar rotation) that would produce faster monthly (or solar rotation) averaged solar wind than the most long‐living coronal holes in each solar cycle produce.

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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: 3
Pages: 2740 - 2747
DOI: 10.1002/2016JA023683
OADOI: https://oadoi.org/10.1002/2016JA023683
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).
Academy of Finland Grant Number: 272157
Detailed Information: 272157 (Academy of Finland Funding decision)
Copyright information: © 2017. American Geophysical Union. All Rights Reserved.