Gleissberg Cycle Dependence of Inner Zone Proton Flux. Issue 7 (19th July 2022)

• Record Type: Journal Article
• Authors: Bregou, Emily J.; Hudson, Mary K.; Kress, Brian T.; Qin, Murong; Selesnick, Richard S.
• Is Part Of: Space weather. Volume 20:Issue 7(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-07-19
• Subjects: Space environment -- Periodicals; 551.509992
• DOI: 10.1029/2022SW003072
• Languages: English
• ISSNs: 1542-7390

Abstract

Abstract: Inner zone proton flux from 1980 to mid‐2021 is examined using NOAA POES satellite data, indicating a long‐term increase 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, serving as proxy for solar EUV input to Earth's atmosphere. Extending an earlier study (Qin et al., 2014; https://doi.org/10.1002/2014JA020300 ) of >70 MeV protons from 1980 – 2021 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. 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 model calculation of the inner zone proton flux is found to generally confirm the long‐term trend examined both in absolute magnitude and phase lag. It is concluded that this long‐term trend is a manifestation of the concurrent Gleissberg cycle minimum and accompanying decrease in solar EUV. Reduced EUV at solar maximum (F10.7 proxy) reduces proton loss to the atmosphere following solar maximum, thus explaining the long‐term flux increase observed. Plain Language Summary: The inner zone proton radiation belt consisting of 10's to >100 MeV protons trapped in the Earth's magnetic field is examined from 1980 to mid‐2021 using measurements from four NOAA POES satellites. A long‐term increase in measured proton flux over four ∼11 years cycles of solar activity is found. This increase correlates with the current one hundred year minimum in solar activity known as the Gleissberg cycle. Inner zone proton flux is correlated with decreasing solar irradiance maxima at a wavelength of 10.7 cm, serving as a proxy for Extreme Ultra Violet input to Earth's atmosphere. It is found that current peak proton flux, occurring at a longitude and latitude where the Earth's magnetic field is weaker, is at the highest levels seen since the beginning of observations in 1980. A model calculation of the inner zone proton flux is found to generally confirm the long‐term trend. We conclude that this trend observed over ∼40 years accompanies an average decrease in solar EUV in comparison with previous solar maxima when EUV irradiation was higher as parametrized by F10.7. The reduced EUV at solar maximum reduces proton loss to the atmosphere, thus explaining the observed long‐term increase in inner zone proton flux. Key Points: POES MeV proton measurements from 1980 to 2021 are anticorrelated with F10.7 Observations are consistent with model prediction of a long term proton flux increase Centennial Gleissberg Cycle solar minimum impact on inner zone proton flux is found