Historical datasets- implications for space weather risk over multiple solar cycles

By obtaining the analytic signal of daily sunspot numbers since 1818 we construct a new solar cycle phase clock that maps each of the last 18 solar cycles onto a single normalized epoch. This clock orders solar coronal activity and can be used to order observations that exist on multiple solar cycles. The aa index tracks geomagnetic storms at the Earth's surface over the last 14 Schwabe cycles, and 'space age' observations are available over several Schwabe cycles: e.g. F10.7 solar radio flux, galactic cosmic ray flux and the GOES flare catalog. We will construct 'clocks' for the (on average) 11 year Schwabe and 22 year Hale cycles to discern systematic Schwabe and Hale cycle variations in these quantities. Analysis of the aa index is desirable given its extent in time, however it is a discretized quantity rather than a well sampled timeseries. New methods to quantify the occurrence rates of extreme events in aa (amplitude information) and in its 27 day recurrence (phase information) are applied in the context of these solar cycle clocks.
S. C. Chapman, S. W. McIntosh, R. J. Leamon, N. W. Watkins, The Sun's magnetic (Hale) cycle and 27 day recurrences in the aa geomagnetic index. Ap. J. submitted (2021) arXiv:2101.02569[astro-ph.SR] S. C. Chapman, S. W. McIntosh, R. J. Leamon, N. W. Watkins, Quantifying the solar cycle modulation of extreme space weather, Geophysical Research Letters, (2020) doi:10.1029/2020GL087795
S. C. Chapman, R. Horne, N. W. Watkins, Using the aa index over the last 14 solar cycles to characterize extreme geomagnetic activity. Geophys. Res. Lett.(2020) doi: 10.1029/2019GL086524