Variability of the spatio/temporal scales in the ionosphere at Swarm altitudes

The ionosphere is a highly dynamical system that shows a complex behaviour due to its nonlinear coupling with the solar wind-magnetosphere system from above and with the lower atmosphere from below. Such a complexity of the ionospheric plasma manifests itself on a largely varying range of spatial and temporal scales. We investigate how the different scales of the in situ electron density recorded at altitudes of Swarm constellation behaves according to the various conditions of the geospace. This, with the scope of finding if the topside ionosphere reacts to an external perturbation as a whole or by activating some peculiar modes.
In this regard, the present study aims at quantifying the spatio-temporal variability in the topside ionosphere by leveraging on the Fast Iterative Filtering (FIF) technique. FIF is able to provide a very fine time-frequency representation, as it decomposes any nonstationary, nonlinear signals, like those provided by Langmuir probes onboard Swarm, into oscillating modes, called intrinsic mode components or functions (IMFs or IMCs), characterized by its specific frequency.
The instantaneous time-frequency representation is provided through the so-called “IMFogram” illustrates the time development of the multi-scale processes. These IMFograms, similarly to spectrograms, have the potential to show the greater details of the scale sizes which intensify during the various phases of geomagnetic storms, as reported during the recent 2015 St. Patrick’s day storm. Scope of the analysis is also to illustrate how the analysis based on the use of FIF and IMFograms provide better performance with respect to similar analysis conducted via Fourier and discrete wavelet transform, by improving the scale resolution.
With this work, we also aim at supporting the development of advanced models of ionospheric plasma variability based on Swarm datasets.
This work is performed in the framework of the Swarm Variability of Ionospheric Plasma (Swarm-VIP) project, funded by ESA in the “Swarm+4D-Ionosphere” framework (ESA Contract No. 4000130562/20/I-DT).