Characterization of the Pc5 frequency range power spectrum at low latitude in 22 years of geomagnetic field observations.

An important aspect of the interaction between the solar wind (SW) and the Earth’s magnetosphere concerns the possible relationship between SW and magnetospheric fluctuations under different SW conditions. In recent investigations (Di Matteo and Villante, 2017,2018) we revealed the critical role of the analytical methods and the spectral analysis techniques in the identification of fluctuations between ≈1-5 mHz in the SW parameters as well as in the magnetospheric field measurements at the geostationary orbit and developed a new approach, based on the joint use of the Welch and the Multitaper methods, for a more robust identification of these oscillations in both regions. Here, we extend the analysis to ground measurements, analyzing 22 years of magnetic field measurements along the H and D components at low latitude (L’Aquila, Italy, λ≈36.3°, L≈1.6). We found that, in general, the much steeper spectrum of the geomagnetic fluctuations with respect to the ones estimated in the SW parameters and magnetospheric field, might deeply influence the identification of real events. We then examined, for the entire period, consecutive two hours intervals through the day during low geomagnetic activity conditions (Dst>-50), and, for each interval, we carefully evaluated the characteristics of the background spectrum. As a matter of fact, in the ≈1-5 mHz frequency range the spectral indices of both components typically range between -3.5 and -2 with a steeper spectrum in the night sector when the fluctuations power is lower. Simulations of red noise representations, with spectral indices similar to the observed ones, combined with the Sq variation show a systematic reduction of the rate of identification of real events up to ≈2 mHz.

Ref.

Di Matteo, S., and U. Villante, J. Geophys.Res. Space Physics, 122, 4905–4920, doi:10.1002/2017JA023936.

Di Matteo, S., and U. Villante, Journal of Geophysical Research: Space Physics, 123, doi.org/10.1002/2017JA024922.