Abstract
This work aims at showing how analysis techniques, designed to highlight the multi−scale structure of a signal, may be of help in de− scribing fluctuations of the ionospheric medium. In particular, the technique used here is the ALIF (Adaptive Local Iterative Filter). We have applied ALIF to the characterisation of plasma irregularities in the equatorward boundary of the auroral oval. The data used are from the LEO satellite DEMETER (Detection of Electro−Magnetic Emissions Transmitted from Earthquake Regions) while it crosses the Equatorward boundary of the oval. The time series analysed are those from the electric field instrument ICE (Instrument de Champ Electrique) on board of DEMETER, and the identification of the equatorward boundary in the time series of in situ data is based on the comparison between the satellite trajectory and the picture of the auroral oval from the simultaneous auroral imaging by the DMSP satellite. In detail, we pre− sent an analysis of the multi−scale features and dynamics of ionospheric plasma along the DEMETER trajectory in different regions, which seem to be characterized by plasma irregularities of different nature. A clear change of the multi−scale nature of plasma fluctuations is observed in the correspondence of the irregularities originated by particle precipitation in the equatorward boundary of the auroral oval.
Highlights
Auroral ovals (AO) are the regions located in the northern and southern high latitude ionosphere where the main particles coming from magnetosphere precipitate [Feldstein, 1963; Feldstein et al, 1969; Akasofu, 1966]
We examine some intervals of in situ data relative to the floating potential Vfloat collected by the ICE (Instrument Champ Electrique, Berthelier et al, (2006)) experiment onboard of the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite [Lagoutte et al, 2006], when the MULTI SCALE ANALYSIS OF THE AURORAL OVAL
Langmuir probes (Lp), performs the various plasma particle collections at different polarization level to obtain the so called I-V characteristic from which it is possible to derive plasma parameters (Chen, 1977)
Summary
Auroral ovals (AO) are the regions located in the northern and southern high latitude ionosphere where the main particles coming from magnetosphere precipitate [Feldstein, 1963; Feldstein et al, 1969; Akasofu, 1966]. These particles interact with the atmospheric atoms and molecules giving rise to luminosity in both visible and ultraviolet spectra. The AO consists in two parts: the discrete oval and the diffuse oval. The last one lies mainly equatorward of the discrete oval, while diffuse precipitation, often not visible, appears poleward of the discrete oval.
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