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Abstract
The engineering-grade magnetic perturbation data from the Iridium satellite constellation, made available through the NSF-funded Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) program, provides unprecedented global coverage for use in magnetosphere-ionospheric-thermosphere research. In this thesis, high-latitude field-aligned current (FAC) patterns are reconstructed from inverse and assimilative analysis of Iridium magnetic perturbation data. New scientific insights on dynamic FAC response to solar wind disturbances are gained from the analysis and FAC patterns and summarized here.
Dominant modes of variability in FACs are associated with categories of solar wind drivers: (1) slow flow; (2) high-speed streams and (3) transient flow associated with coronal mass ejections (CMEs) and (4) all solar wind drivers combined. These are found using empirical orthogonal function (EOF) analysis. Correlations with the interplanetary magnetic field (IMF), solar wind plasma and solar wind-magnetosphere coupling are found for different solar wind drivers and EOFs. The two hemispheres show interhemispheric asymmetries in both spatial patterns and correlation with drivers. The EOFs are then used to construct a fixed background model and background error covariance for use in an optimal interpolation (OI) method. FAC patterns are reconstructed in two hemispheres with a 2-min cadence for two event studies with this procedure. Examples of intriguing FAC patterns under different IMF and solar wind conditions are presented. Interplanetary (IP) shocks, which are a category of strong solar wind disturbance, are studied using superposed epoch analysis. The geoeffectiveness of (1) nearly frontal shocks (NFS) where the IP shock hits the Earth head on and (2) highly inclined shocks (HIS) where the IP shock hits the Earth with a large inclination is examined in terms of the difference in high-latitude FACs response. Results derived from observations verify earlier findings from simulations that NFSs result in sharper increase in FACs and higher total currents. NFSs are in general stronger shocks than HISs in terms of solar wind parameters and therefore cause stronger FAC response. Noon, dusk and pre-noon regions are found to show the most notable difference in FAC response to the two groups of shocks, which can be valuable information for space weather application.
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