Proton flux variations during Solar Energetic Particle Events, minimum
and maximum solar activity, and splitting of the proton belt in the
South Atlantic Anomaly
The analysis of the proton flux variations observed by the Energetic
Particle Telescope (EPT) at energies > 9.5 MeV from the
launch of PROBA-V satellite on 7 May 2013 up to October 2022 shows an
anti-correlation between the proton fluxes and the solar phase. At solar
minimum, the fluxes are higher at low L corresponding to the northern
border of the South Atlantic Anomaly (SAA). This solar cycle modulation
of the inner belt is mainly due to losses by increased atmospheric
interactions during solar maximum.
Strong Solar Energetic Particle (SEP) events, like in January 2014, June
2015 and September 2017, inject energetic protons at high latitudes, but
not in the inner belt where protons are trapped at long term at low L.
Nevertheless, big geomagnetic storms, including those following SEP a
few days after, can cause losses of protons at the outer border of the
proton belt, due to magnetic field perturbations.
A double peak in the proton belt is observed during long period of
measurements for the EPT channel of 9.5-13 MeV. The narrow gap between
the two peaks in the inner belt is located around L=2. This resembles to
a splitting of the proton belt, separating the SAA into two different
parts, North and South.
The high-resolution measurements of PROBA-V/EPT allow the observation of
small-scale structures that brings new elements to the understanding of
the different source and loss mechanisms acting on the proton radiation
belt at LEO.