Long Term High Energy Electron Dynamics in The Inner Zone
Long Term High Energy Electron Dynamics in The Inner Zone
Tuesday, 6 March 2018: 11:10
Longshot and Bogey (Hotel Quinta da Marinha)
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Abstract:
The presence of high energy electrons in the inner zone of the radiation belt and their dynamics is still a debate. Using MagEIS measurements on board the Van Allen Probes, Fennell et al. claimed their absence, or at least the fact that their level must be below the background of the instrument. On the other hand, Selesnik showed their presence during a limited period of time, but also their variations from SAMPEX-PET measurements. Nevertheless due to the orbit of the spacecraft, the conclusion was limited in L range and in energy range. Recently, Claudepierre et al. improved the analysis of MagEIS data in the inner zone and came back to the first conclusion about the absence of electrons, and showed that this zone can be filled with electrons, following strong magnetic storms.
In this study we extend such an analysis to decades to find out how often could the inner region be filled up by energetic electrons and how fast their decay was. In a first step, SEM measurements made on board the NOAA operational satellites (6 to 14) between 1978 and 2004 are used, to search clues of the slot filling for E>1.2MeV. At least six major events were found and correspond to strong to extreme storms. The inner energetic electron belt profile were then compared to specification models and measurements made by CRRES before and after March 1991. In a second step, we used a simplified version of the dynamic physical model of the electron belt, SALAMMBO, to better understand the long term dynamics of the inner zone electrons. It solves the 2D diffusion equation for equatorial. The model considered a constant boundary condition, a time dependent radial diffusion and losses which are due to waves and interactions with neutrals and plasma from the thermosphere-exosphere and the ionosphere. With this simple physical model, with no wave-particle acceleration, it has been possible to show how the succession of storms during solar maximum phase lead to energetic electron enhancements in the inner belt and at which rate they vanish during the decrease of activity toward solar minimum. It also shows that the conjunction of the last long solar minimum and the weak solar maximum encountered at present induce very low levels of electrons in the inner belt, the lowest observed in the last decades, and why it is very hard to measure them presently.
In this study we extend such an analysis to decades to find out how often could the inner region be filled up by energetic electrons and how fast their decay was. In a first step, SEM measurements made on board the NOAA operational satellites (6 to 14) between 1978 and 2004 are used, to search clues of the slot filling for E>1.2MeV. At least six major events were found and correspond to strong to extreme storms. The inner energetic electron belt profile were then compared to specification models and measurements made by CRRES before and after March 1991. In a second step, we used a simplified version of the dynamic physical model of the electron belt, SALAMMBO, to better understand the long term dynamics of the inner zone electrons. It solves the 2D diffusion equation for equatorial. The model considered a constant boundary condition, a time dependent radial diffusion and losses which are due to waves and interactions with neutrals and plasma from the thermosphere-exosphere and the ionosphere. With this simple physical model, with no wave-particle acceleration, it has been possible to show how the succession of storms during solar maximum phase lead to energetic electron enhancements in the inner belt and at which rate they vanish during the decrease of activity toward solar minimum. It also shows that the conjunction of the last long solar minimum and the weak solar maximum encountered at present induce very low levels of electrons in the inner belt, the lowest observed in the last decades, and why it is very hard to measure them presently.