Abstract
Abstract. With the energetic particle telescope (EPT) performing with direct electron and proton discrimination on board the ESA satellite PROBA-V, we analyze the high-resolution 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.
Highlights
Discovered by James Van Allen (Van Allen and Franck, 1959), the terrestrial radiation belts are toroidal regions surrounding Earth and filled with very energetic electrons and protons from hundreds of keV to hundreds of MeV trapped in the magnetic field of the Earth
Associated to recent observations of Van Allen Probe spacecraft, our results show that the radiation belts are sometimes different from the general feature
The event of 17 March 2015 is the highest geomagnetic storm that has been observed since the launch of PROBA-V in May 2013, with a Dst index as low as −223 nT
Summary
Discovered by James Van Allen (Van Allen and Franck, 1959), the terrestrial radiation belts are toroidal regions surrounding Earth and filled with very energetic electrons and protons from hundreds of keV to hundreds of MeV trapped in the magnetic field of the Earth. Observations of the outer electron radiation belt often show dropouts, i.e., sudden electron depletions during the main phase of storms, followed by injections occurring at lower radial distances. These changes in the radiation belt flux are driven by the interaction of the solar wind with the Earth’s magnetosphere and can occasionally fill-in the slot region (Lemaire et al, 1996). Note that a third radiation belt was recently observed just after the launch of the two Van Allen Probes for energetic electrons (> 2 MeV), from 2 September 2013 and with a duration of around 4 weeks (Baker et al, 2013) During the first half of 2015, several geomagnetic storms have modified the space radiations around the Earth, as described in the present work based on observations of the new performant EPT instrument that provides well discriminated flux measurements of electrons and protons
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