GNGTS 2014 - Atti del 33° Convegno Nazionale

28 GNGTS 2014 S essione 2.1 on data coming from satellite missions lasting only a few months or collected a few months with equal attitude data, therein providing weak evidence for correlations with earthquakes (Sgrigna et al. , 2005; Aleksandrin et al. , 2003). These flux variations have been interpreted as pitch angle diffusions induced by Coulomb scattering (Walt and Farley, 1976) and resonant wave-particle interactions (Aberl and Thorne, 1998). However, the theoretical explanation for the flux variations are still being elaborated upon (Albert and Bortnik, 2009). The NOAA particle database had already been studied by means of particle bursts in connection with global seismic activity during quiet solar periods (Fidani et al. , 2008). Exceptional increasings of particle fluxes were discovered in connection with the largest quakes that struck the Indonesian region over the last two decades. Contiguous particle bursts as singlle events were also studied. In order to distinguish correlations with seismic activity from seasonal variations of particle flux and solar activity, the geomagnetic indexes Ap, kp and Dst where considered. Moreover, earthquake clustering was initially included to study the types and causes of false correlations (Fidani et al. , 2010). Finally, their auto-correlations were investigated (Fidani et al. , 2012). The NOAA particles fall into a lower range of energy, compared to previously observed particle precipitations associated with earthquakes (Galperin et al. , 1992; Boskova et al ., 1994; Ruzhin et al. , 1998). The particle database contains from 30 keV to a few MeV electron and proton counting rates (Evans and Greer, 2004), which is similar to DEMETER IDP (Sauvad et al. , 2006). A criterion to select electron bursts has been applied on high energy electron flux data at 70 keV–2.34 MeV recorded by IDP on DEMETER (Zhang et al. , 2013). In this study, the calculated time differences between counting rates and earthquakes were longer than those of previously published works, and increases in energetic electron fluxes were observed a few days before earthquakes (Anagnostopoulos et al. , 2010), accompanied by broadband kHz emissions (Zhang et al. , 2012) and compared to the VLF transmitter contributions (Sidiropoulos et al. , 2011;). Furthermore, a statistical similarity between high energy charged particle fluxes detected by DEMETZER and earthquakes has also been reported (Wang et al. , 2014). Being so, complete correlation analysis was applied to NOAA database to verify a non-casual association of particle precipitation with large seismic events. Data preparation and analysis . The NOAA archive record covers a measurement period of 32 s of data (Evans and Greer, 2004), including a full set of orbital parameters provided every 8 s. In addition, satellite latitude, longitude and altitude are provided every 2 seconds. The archive record include 16 full data collection cycles from the MEPED electron and proton telescope instruments, so they are provided every 2 s with a sampling interval of 1 second. A selected portion of the SEM-2 instrument status, temperature, and system health data as well as data quality and ancillary information, are included. Unreliable counting rates were excluded from the analysis using flags signalling errors in NOAA detectors. Since the energy for the electrons is a cumulative sum over three thresholds equal to E1 = 30 keV, E2 = 100 keV and E3 = 300 keV, and the energy interval was determinant for the scope of this analysis to consider the best defined energies, new energy channels derived from the difference of the energies thresholds were defined for the intervals 30–100 keV, 100–300 keV and >300 keV. As all sets of orbital parameters were provided at least every 8 s, this value was chosen as the basic time step of the study. Consequently, all other variables were defined in the 8 s time step. Thus, 8 s averages of counting rate, latitude, longitude, MEPED and omnidirectional data were calculated. The first step in the preparation of NOAA data consisted in the storage of all binary files into Ntuples (Couet, 1998) where the time step was 8 s. From July 1, 1998 to June 30, 2011, binary data were downloaded from NOAA (http://www.ngdc.noaa.gov/stp/satellite/poes/dataaccess.html) and examined to exclude uncorrected instrument operations through their corresponding flags. Inner belt particle flux increases by over one order of magnitude were always observed during the main phase of magnetic storms (Tadokoro et al. , 2007), which occur in rapid response (< 1 day) of the inner VanAllen Belts to the solar wind velocity peak (Vassiliadis, 2008). Sudden