Publications

First, we show that a contamination of the experimental results, dramatic in statistical investigations, might come from the rotation of measurements in the field-aligned coordinates when the field direction is determined, point by point, by the running averages: this procedure creates spurious events at frequencies related to the length of the running average window. These aspects do not appear in a fixed coordinate system, as determined by evaluating the average field vector for the entire interval. In this system, we examined 124 magnetospheric structures following sudden impulses and found some evidence for higher percentages of events occurs at f ≈ 1.5–1.7, f ≈ 2.2–2.4, ≈3.9–4.2, and, more explicitly, at f ≈ 4.2–4.7 mHz.

We focused attention on the fluctuations of the SW dynamic pressure (PSW) occurring in the leading edges of streams following interplanetary shocks and compared the results of the Welch method (WM) with those of the multitaper method (MTM). The results of a simulation analysis demonstrate that the identification of the wave occurrence and the frequency estimate might be strongly influenced by the signal characteristics and analytical methods. The histogram of the frequency distribution of the events identified by both methods suggests more relevant percentages between f ≈ 1.7–1.9, f ≈ 2.7–3.4, and f ≈ 3.9–4.4 (with a most relevant peak at f ≈ 4.2 mHz).

We present a new spectral analysis method for the identification of periodic signals in geophysical time series. We demonstrate the algorithm on Monte Carlo simulations of synthetic time series and a case study of magnetospheric field fluctuations directly driven by periodic density structures in the solar wind. The method is robust and flexible. Our procedure is freely available as a stand-alone IDL code at https://zenodo.org/record/3703168.

Following previous investigations of quasiperiodic plasma density structures in the solar wind at 1 AU, we show using the Helios1 and Helios2 data their first identification in situ in the inner heliosphere at 0.3, 0.4, and 0.6 AU. We present five events of quasiperiodic density structures with time scales ranging from a few minutes to a couple of hours in slow solar wind streams. Where possible, we locate the solar source region of these events using photospheric field maps from the Mount Wilson Observatory as input for the Wang-Sheeley-Arge model.

This paper presents a new model, called MA.I.GIC. (Magnetosphere-Ionosphere-Ground-Induced Current), to derive the geoelectric field used to determine the magnitude of GICs. In addition, we discuss the results of the MA.I.GIC. model applied to the September 2017 Geomagnetic Storm with particular focus on the two sudden impulses occurring on 6 and 7 September 2017, and the two main phases on 7 and 8 September 2017.