Abstract. With the energetic particle telescope (EPT) performing with direct electron and proton discrimination on board the ESA satellite PROBA-V, we analyze the highresolution measurements of the charged particle radiation environment at an altitude of 820 km for the year 2015. On 17 March 2015, a big geomagnetic storm event injected unusual fluxes up to low radial distances in the radiation belts. EPT electron measurements show a deep dropout at L>4 starting during the main phase of the storm, associated to the penetration of high energy fluxes at L<2 completely filling the slot region. After 10 days, the formation of a new slot around L = 2.8 for electrons of 500-600 keV separates the outer belt from the belt extending at other longitudes than the South Atlantic Anomaly. Two other major events appeared in January and June 2015, again with injections of electrons in the inner belt, contrary to what was observed in 2013 and 2014. These observations open many perspectives to better understand the source and loss mechanisms, and particularly concerning the formation of three belts.
The Energetic Particle Telescope (EPT) is a new compact and modular ionizing particle spectrometer that was launched on 7 May 2013 to a LEO polar orbit at an altitude of 820 km onboard the ESA satellite PROBA-V. First results show electron, proton and helium ion fluxes in the South Atlantic Anomaly (SAA) and at high latitudes, with high flux increases during SEP (Solar Energetic Particles) events and geomagnetic storms. These observations help to improve the understanding of generation and loss processes associated to the Van Allen radiation belts.
Using the observations of the EPT (Energetic Particle Telescope) onboard the satellite PROBA-V, we study the dynamics of inner and outer belt electrons from 500 keV to 8 MeV during quiet periods and geomagnetic storms. This high time-resolution (2-s) spectrometer operating at the altitude of 820 km on a low polar orbit is providing continuously valuable electrons fluxes for already 5 years. We emphasize especially that some megaeleactron volt electrons are observed in low quantities in the inner belt, even during periods when they are not observed by Van Allen Probes. We show that they are not due to proton contamination but to clear injections of particles from the outer belt during strong geomagnetic storms of March and June 2015, and September 2017. Electrons with lower energy are injected also during less strong storms and the L shell of the electron flux peak in the outer belt shifts inward with a high dependence on the electron energy. With the new high-resolution EPT instrument, we can study the dynamics of relativistic electrons, including megaelectron volt electrons in the inner radiation belt, revealing how and when such electrons are injected into the inner belt and how long they reside there before being scattered into the Earth's atmosphere or lost by other mechanisms.Plain Language Summary New high resolution EPT/PROBA-V measurements of the electrons fluxes allow us to better understand the dynamics of the electrons in the inner and outer radiation belts. EPT put in perspective the VAP discovery that the expected population of MeV electrons in the inner belt was "missing" and that previous studies suggesting a long-lived, relatively static inner radiation belts likely misidentified penetrating protons as inner belt electrons. Some MeV electrons are observed by EPT in the inner belt, but in very low quantity. This observation of EPT cannot be due to proton contamination since injections associated to geomagnetic storms are clearly identified. The new capability of EPT to well discriminate the particle species and energy ranges led to new discoveries concerning their source and loss mechanisms regarding the dynamics in this region.
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