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Causes of non-stationary relationships between geomagnetic activity and the North Atlantic Oscillation
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SYSNO ASEP 0502274 Document Type J - Journal Article R&D Document Type Journal Article Subsidiary J Článek ve WOS Title Causes of non-stationary relationships between geomagnetic activity and the North Atlantic Oscillation Author(s) Bucha, Václav (GFU-E) ORCID, RID Source Title Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier - ISSN 1364-6826
Roč. 188, April (2019), s. 43-49Number of pages 7 s. Publication form Print - P Language eng - English Country GB - United Kingdom Keywords North Atlantic Oscillation ; geomagnetic activity ; stratospheric polar vortex ; descending pressure anomalies Subject RIV DE - Earth Magnetism, Geodesy, Geography OECD category Climatic research Method of publishing Limited access Institutional support GFU-E - RVO:67985530 UT WOS 000461405100005 EID SCOPUS 85061402276 DOI 10.1016/j.jastp.2019.01.017 Annotation The North Atlantic Oscillation (NAO) is known to be influenced by internal variability of the atmosphere and the ocean and respond to natural or anthropogenic external forcing. However, there is no consensus on the exact mechanisms. The NAO correlates with geomagnetic activity (considered as the parameter for the solar wind intensity) positively during one period (i.e. 1951-1996) but negatively in another period (i.e.1870-1950), making the Sun-climate connection a controversial subject. We try to explain this non-stationary relationship and to find the causes why the correlation had changed the sign during the past 148 years. At the times of low geomagnetic activity before 1950 and after 1997 the correlation between geomagnetic activity and the NAO was relatively weak. The variability of the NAO during those periods was mainly due to other processes. In order to answer the question why a more positive NAO phase has prevailed over the last 30 years of the past century, we study the geomagnetic signal near the surface conditioning upon the strength, shape and location of the stratospheric polar vortex and examine the immediate effect of geomagnetic storms in the troposphere. At times of prevailing high geomagnetic activity (1951-1996) the polar vortex strengthened. The effect of the solar wind was mainly over northern Europe in association with the positive phase of the NAO. A strengthened mid-latitude westerly jet kept the cold air in the Arctic and northern mid-latitudes became milder than average. When geomagnetic activity decreased, the stratospheric polar vortex also weakened. The solar wind signal prevailed over Canada in association with the negative NAO index and more of Arctic air was able to penetrate North America and Eurasia. We finally show that the geomagnetic storms may play a role in the acceleration of the downward penetration of pressure anomalies from the upper stratosphere into the troposphere. Workplace Geophysical Institute Contact Hana Krejzlíková, kniha@ig.cas.cz, Tel.: 267 103 028 Year of Publishing 2020 Electronic address https://www.sciencedirect.com/science/article/abs/pii/S136468261830378X?via%3Dihub
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