Understanding the secular variability of solar irradiance: the potential of Ca II K observations | Journal of Space Weather and Space Climate

Topical Issue - Space Climate: Long-term effects of solar variability on the Earth’s environment

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Table 1

Comparison between selected photometric sum series in Ca II K.

Series	Mean relative	Mean absolute relative	RMS	R	R ²
Chatzistergos et al. (2020a) SFO – Chatzistergos et al. (2020a) Rome/PSPT	0.016	0.11	1312	0.98	0.95
Chapman et al. (2013) SFO – Chatzistergos et al. (2020a) SFO	0.010	0.10	1331	0.97	0.95
Chapman et al. (2013) SFO – Chatzistergos et al. (2020a) SFO	0.021	0.12	1176	0.98	0.96

Note. Shown are mean relative, mean absolute relative, and RMS differences [Wm⁻²] as well as the linear correlation coefficient, R, and R². The differences are computed after linearly scaling the photometric sum series to match those from Rome/PSPT (shown as dashed lines in Fig. 6).

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