GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.1 GNGTS 2023 number of EBs to be considered. The primary cause of precipitating electrons is solar activity when solar wind velocity variations impact the magnetosphere (Vassiliadis, 2008). Being so, days of moderate to high solar activity were excluded from the analysis by neglecting data when the daily Ap index overcame a threshold. The threshold was set according to the seasons and years due to the solar cycle using the relation Ap = 11.1 + 0.8 sin [0.37(year − 1996)] + {2.1 − 0.1 sin[0.37(year − 1996)]} cos [0.0172(day − 27)]. In fact, the phase shift defined by the above relation matched the minimum of the Sun’s activity in 199, while the 27-day modulation was dictated by the Sun’s rotation. The Dst index was also included to reduce the solar influence, it was reflecting the substorm activity (Lam et al., 2010) and was considered a limit lower than − 27 nT. As a further investigation of the solar influence on electron precipitation, the Auroral Electrojet (AE) index (Anderson and Chen, 2002) was taken into consideration. The AE index quantifies the magnetic activity produced by enhanced Ionospheric currents flowing below and within the auroral oval, as the deviation from quiet day values of the horizontal geomagnetic field. It is directly related to the processes producing the observed geomagnetic variations and can be defined instantaneously, other than to be related to the sub-storm activity. The AE index was then compared to the electron losses detected by NOAA and to the selected EBs to quantify a possible dependence between AE and EBs. In this way discarding the related events to external geomagnetic variation and reducing false alarms. Fig. 3. The AE index was downloaded with an hourly rate at https://wdc.kugi.kyoto-u.ac.jp/aedir/ relative to the same period of the correlation from July 1998 to December 2014. References Anderson, P. C., and Chen, M. W.; 2002: Examination of the storm/substorm relationship using global auroral X-ray images . J. Geophys. Res., 107 , A10, 1326, doi:10.1029/2001JA009184. Console, R.; 2001: Testing Earthquake Forecast Hypotheses . Tectonophysics 338 , 261–268. doi:10.1016/s0040-1951(01)00081-6. Fidani, C.; 2021: West Pacific earthquake forecasting by NOAA electron bursts with independent L-shells and ground-based magnetic correlations. Frontiers in Earth Science, 9 , 673105.