Predictions of ionizing radiation in space during storm-time

by L. Mazzino



Magnetic storms and their subsequent energetic particle flux enhancements constitute an important issue dealt with in space weather studies. These very energetic particles are especially important for space missions since they can damage solar panels and electronics of satellites. Empirical models of the space radiation environment have been developed but flux predictions from these models are mainly static and quite inaccurate, especially below 1000 km, where discrepancies with observed energetic proton fluxes can reach an order of magnitude. Important differences appear in the radiation belts during geomagnetic storms and substorms, with sometimes creation of several inner belts. These flux variations significantly contribute to the increased variances that spoil statistical ionizing radiation flux models, i.e, results of flux measurements at a given position in space can only be accurately predicted if the past geomagnetic activity is well specified. Therefore, the RABEM/SEVEM particle and wave dynamical model is based on the assumption that the particle fluxes and wave intensities at a given position in space are composed of a steady state background and a magnetic activity-dependent value that is a function of the elapsed time after the latest geomagnetic storm (GS), the intensity of the latest GS, the flux level prior to the latest GS, the local flux decay time and the occurrence probability for a new GS. Fifty years of GS events characterized by their minimum Dst have been analyzed and the statistics distribution of time intervals between GS along with their magnitude were derived at several times within the solar cycle. Flux data from different sources are analyzed to establish a relationship between flux enhancement and storm characteristics. In particular, using the DEMETER flux data, we have identified GS events in 2004, where the magnitude of the maximum flux enhancement goes in hand with the magnitude of the storms, for electrons between 0.521 and 0.968 MeV for L>3 and B>0.22 nT. In addition, decay times of fluxes have been evaluated as a function of energy and position. The steps accomplished during the ongoing RABEM/SEVEM model development activity will be described and preliminary results of the study will be presented.
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