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Title: The use of geomagnetic activity observations in studies of solar wind-magnetosphere coupling and centennial solar change
Author: Finch, Ivan
ISNI:       0000 0001 3464 9594
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2008
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The source of the semi-annual variation in geomagnetic indices is investigated with regard to its possible origins in the solar wind and within the magnetosphere/ionosphere system. To further this investigation, the patterns of annual' and diurnal variations of the existing long-running aa and am indices are modelled and the stability of the semi-annual variation over the last 150 years confirmed. The connection between these range indices and the solar wind is evaluated at a wide variety of timescales, varying from 3 hours to 1 year, in order to determine which of the solar wind parameters are responsible for their variations. In this respect, the importance of considering discontinuities in the in-situ data from spacecraft in the solar wind is highlighted. The asymmetry of the two equinox peaks in geomagnetic activity is used to investigate thel axial hypothesis which links the semi-annual variation seen at the Earth to a proposed latitudinally-symmetrical structure of the Sun. It is demonstrated that during the spacecraft era the assumptions underpinning this model are false and that the Earth's sampling of the solar wind has been strongly influenced by solar structure asymmetries and variations on timescales shorter than Earth's annual orbit. The results strongly suggest that these asymmetries arose by chance and so little information about the Sun can be gained from the asymmetries seen in the aa index over the past century and a half. A new geomagnetic index is constructed to characterise more fully the semi-annual variation of the terrestrial current systems. Using this index it is confirmed that the equinoctial hypothesis which best characterises the semi-annual variation of activity is a process internal to the magnetosphere (specifically the substorm current wedge) and not a product of annual and diurnal modulations of energy extraction from the solar wind.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available