Fraction of the mission time where the proton flux measured by SREM (F) is above a certain flux value. The proton fluxes (E> 120 MeV) are measured by the Solar Radiation Environment Monitor onboard Planck in the 2009−2013 time span. The flux drops rapidly around the mean value foreseen by Creme96 in the same timespan (vertical dashed line), while the second plateau (above ~3 cts cm^-2 s^-1) depicts the contribution of solar flares. The vertical dotted line shows the ACD threshold flux value where DT > 5%.