Costel Bunescu

• Aurora is the most visible result of the dynamic processes associated to the magnetosphere-ionosphere coupling at high altitudes. Field-aligned currents (FACs) are the main coupling agent that mediate the energy and momentum transfer between the magnetospheric and ionospheric plasma. FACs are directly connected to auroral structures covering a large range of temporal and spatial scales, as well as various geometries. The observed spatial scales of FACs range from small scales (0.1-1 km) up to mesoscales and large scales (10-100 km and more). The first goal of the thesis is to extend basic analysis methods, by tailoring them to a multiscale approach, appropriate for the study of the complex FACs associated with aurora. We introduce the multiscale FAC analyzer, based on multiscale minimum variance analysis (MVA) of the FAC signatures. This technique relies on performing the classical MVA continuously and over a range of scales, by varying the width of the analysis window, and provides multiscale information on the planarity and orientation of the FACs. The derivative of the largest eigenvalue of the magnetic variance matrix with respect to the width of the analysis window provides the location and thickness of the planar FACs. The second goal is to develop an analysis technique that integrates multiple measurements taken from different observation platforms in order to investigate the dynamics of quasi-periodic FACs. We introduce a new approach to examine the azimuthal (east-west) dynamics of quasi-periodic FACs based on the analysis of the Doppler shifts between different observation points (on ground and in space). This technique provides information on the dependence of the wavelength (or propagation velocity) on the wavefront propagation direction of the FACs. The examination of conjugate data from high- and low-altitude satellites, as well as from ground, makes if possible to cross-check the Doppler analysis and to further constrain the azimuthal motion.