Fig. 1: The Southern-Hemisphere 14CO measurements and model results and the solar modulation parameter as functions of time.
From: Radiocarbon monoxide indicates increasing atmospheric oxidizing capacity

(red) 14CO measurements at (a) Baring Head and (b) Arrival Heights. The red vertical bars reflect the standard measurement errors. (black solid lines) Monthly-mean surface 14CO, interpolated to the locations of Baring Head and Arrival Heights, as simulated by the NIWA-UKCA model (see below and section “ Galactic 14C production and the NIWA-UKCA model”). c Monthly-mean “solar modulation parameter" (SMP, in MeV) since 1989 (https://cosmicrays.oulu.fi/phi/Phi_Table_2017.txt). The blue digits and vertical bars conventionally enumerate and bound, respectively, the solar cycles (https://www.spaceweather.com/en/solar-activity/solar-cycle/historical-solar-cycles.html).