Stepping into the Equatorward Boundary of the Auroral Oval: preliminary results of multi scale statistical analysis

摘要

This work aims at showing how analysis techniques highlighting the multi-scale structure of a signal, as the technique ALIF (Adaptive Local Iterative Filter) used here, may be of help in describing the ionospheric medium fluctuations. In particular, the case study at hand clearly shows how such a local analysis of the medium may register the encounter of a LEO satellite with topside ionospheric irregularities met in the Equatorward Boundary (EWB) of the Auroral Oval, entering the region were geomagnetic lines are not dipolar any more, but rather stretched towards the magnetic tail. A data segment is analysed, collected by the LEO satellite DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions), in the correspondence of the orbit segment crossing the low latitude boundary of the Auroal Oval in the post-sunset sector of January 1, 2005. Even if DEMETER flies at 700 km, i.e. well above the region in which auroral luminescence is originated, it is very likely that the irregular structure met in the time series of data from its ICE (Instrument Champ Electrique) instrument corresponds to plasma irregularities originated by the same particle precipitation switching on the Northern Light hundreds of kilometres below. In the time interval considered the LEO appears to go through very different plasma structures, and the data segment it collects is characterised by non-stationary fluctuations. In particular, in EWB, plasma acquires space-irregularity corresponding to the high velocity shear of particles precipitation.