Centennial evolution of monthly solar wind speeds:fastest monthly solar wind speeds from long‐duration coronal holes
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 prox...
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ftunivoulu:oai:oulu.fi:nbnfi-fe201903057167 2023-07-30T04:06:49+02:00 Centennial evolution of monthly solar wind speeds:fastest monthly solar wind speeds from long‐duration coronal holes Lukianova, R. (Renata) Holappa, L. (Lauri) Mursula, K. (Kalevi) 2017 application/pdf http://urn.fi/urn:nbn:fi-fe201903057167 eng eng American Geophysical Union info:eu-repo/semantics/openAccess © 2017. American Geophysical Union. All Rights Reserved. info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion 2017 ftunivoulu 2023-07-08T19:55:26Z 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. Article in Journal/Newspaper Sodankylä Jultika - University of Oulu repository Sodankylä ENVELOPE(26.600,26.600,67.417,67.417) |
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Open Polar |
collection |
Jultika - University of Oulu repository |
op_collection_id |
ftunivoulu |
language |
English |
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. |
format |
Article in Journal/Newspaper |
author |
Lukianova, R. (Renata) Holappa, L. (Lauri) Mursula, K. (Kalevi) |
spellingShingle |
Lukianova, R. (Renata) Holappa, L. (Lauri) Mursula, K. (Kalevi) Centennial evolution of monthly solar wind speeds:fastest monthly solar wind speeds from long‐duration coronal holes |
author_facet |
Lukianova, R. (Renata) Holappa, L. (Lauri) Mursula, K. (Kalevi) |
author_sort |
Lukianova, R. (Renata) |
title |
Centennial evolution of monthly solar wind speeds:fastest monthly solar wind speeds from long‐duration coronal holes |
title_short |
Centennial evolution of monthly solar wind speeds:fastest monthly solar wind speeds from long‐duration coronal holes |
title_full |
Centennial evolution of monthly solar wind speeds:fastest monthly solar wind speeds from long‐duration coronal holes |
title_fullStr |
Centennial evolution of monthly solar wind speeds:fastest monthly solar wind speeds from long‐duration coronal holes |
title_full_unstemmed |
Centennial evolution of monthly solar wind speeds:fastest monthly solar wind speeds from long‐duration coronal holes |
title_sort |
centennial evolution of monthly solar wind speeds:fastest monthly solar wind speeds from long‐duration coronal holes |
publisher |
American Geophysical Union |
publishDate |
2017 |
url |
http://urn.fi/urn:nbn:fi-fe201903057167 |
long_lat |
ENVELOPE(26.600,26.600,67.417,67.417) |
geographic |
Sodankylä |
geographic_facet |
Sodankylä |
genre |
Sodankylä |
genre_facet |
Sodankylä |
op_rights |
info:eu-repo/semantics/openAccess © 2017. American Geophysical Union. All Rights Reserved. |
_version_ |
1772819745149550592 |