Turnover in Gleissberg Cycle Dependence of Inner Zone Proton Flux

LASP Magnetosphere Seminars

Turnover in Gleissberg Cycle Dependence of Inner Zone Proton Flux

Mary Hudson
(Dartmouth College, HAO NCAR)
January 30, 2024 2:00 PM

Inner zone proton flux from 1980 to mid-2023 has been examined using NOAA POES satellite data, extending analysis by Bregou et al (2022), who found a long-term increase in proton flux averaged over the 11-year solar cycle modulation corresponding to a one hundred year minimum in solar activity consistent with the Centennial Gleissberg Cycle. Variation of inner belt protons is correlated with decreasing F10.7 maxima over the 40-year period up to 2021, serving as proxy for solar EUV input to Earth’s atmosphere. Extending an earlier study (Qin et al., 2014) of >70 MeV protons using the South Atlantic Anomaly (SAA) peak flux, and at fixed L = 1.3, a comparison is made between the >35, >70 and >140 MeV energy channels on POES. All three energies show an increase in proton flux over the period 1998 – 2021 using a single spacecraft. The observed flux increase is correlated with decreasing F10.7 over the longer 40-year time interval, as with the ∼11-year solar cycle. Most recently the proton flux in all three energy channels has dropped with the rapid rise in F10.7 for Solar Cycle 25. A phase lag during Solar Cycle 24 (January 2010 – June 2021) between the F10.7 minimum and proton flux maximum was determined to be ∼500 days, the same at all energies studied. A comparable phase lag is found between the December 2019 solar minimum and the inner zone proton peak flux observed in 2021. A model calculation of the inner zone proton flux was found to generally confirm the long-term trend examined by Bregou et al. (2021) both in absolute magnitude and phase lag. It is concluded that this long-term trend is a manifestation of the Gleissberg Cycle minimum and accompanying decrease in solar EUV. Increased EUV as we approach the Solar Cycle 25 maximum (using F10.7 as a proxy) has led to increased proton loss to the atmosphere and resulting turnover of the long-term trend of increasing inner zone proton flux observed over the preceding four solar cycles.

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