Turnover in Gleissberg Cycle dependence of inner zone proton flux

A previous study found a long‐term increase in proton flux averaged over the 11‐year solar cycle oscillation corresponding to solar activity consistent with the Centennial Gleissberg Cycle (CGC). F10.7 flux maxima have been decreasing over the ∼40‐year period of 1980–2021, correlating with an average increase in the varying proton population.

Bregou et al. ’s (2022, doi.org/10.1029/2022sw003072 ) long‐term study of the peak flux over the SAA in NOAA‐15 shows an increase in proton flux from 1998 until 2021. The observed flux increase is correlated with both the ∼11‐year solar cycle and the overall decreasing F10.7 flux over the period studied. This long‐term decrease in F10.7 flux and increase in proton flux is concluded to be the manifestation of the CGC minimum and accompanying decrease in solar Extreme Ultraviolet irradiance (EUV).