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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-24 6:17 |
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Conference: Bucharest University Faculty of Physics 2008 Meeting
Section: Nuclear and Elementary Particles Physics
Title:
Periodicity of the Aa Geomagnetic Index
Authors:
Cristina Pirvutoiu, Dan Nicolae Vladoiu
Affiliation:
Institute of Geodynamics, Bucharest
E-mail
cristina.pirvutoiu@brahms.fizica.unibuc.ro, dan_vladoiu_nicolae@yahoo.com
Keywords:
geomagnetic indices, Wolf number, solar cycles
Abstract:
A number of geomagnetic indices have been introduced to describe the variation of the geomagnetic field as a response to the variable conditions in the solar wind. The most important imprint on the terrestrial magnetosphere belongs to the high speed streams in solar wind which are transferrihg part of their energy to the magnetosphere.
The paper analyses the Aa geomagnetic index during 1964 – 2007 period that includes four 11-years solar cycles (nos. 20 – 23) and two magnetic solar cycles (Hale cycle or 22-year solar cycle).
The 11-year solar cycles, analyzed by the monthly values of the sunspot relativ number (Wolf number), are quite differents by their intensity and durations. The pairs of two such cycles (nos. 20 and 21, nos. 22 and 23, respectively) constitue 22-year solar magnetic cycles; their properties are also noticed. The particularities of the Aa series are detailed in comparison with each solar cycle. The Aa series present a more complex variability during the analysed period, with more maxima. Some of these maxima are placed nearby the sunspot maxima of the 11-year solar cycles but the most important of them are placed on the descendant phase of the solar cycle. The last ones could be explained as a consequences of the variabilities registered by the high speed stream parameters during the corresponding phase of solar cycle..
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