Comment on ‘ ‘ Testing Hypotheses about Sun - Climate

Rypdal and Rypdal (RR) [1] assert that the hypothesized linking between the Sun and climate complexity, first suggested by Scafetta and West (SW) [2] and developed in subsequent publications [3–6], is not supported by data. However, RR employed Lévy Flight noise in their analysis instead of the Lévy Walk (LW) signal used by SW. In fact, RR focused on the statistics of increments while SW focused on the statistics of the time intervals. RR stress the rapid fluctuations within a record, while SW stress the slow trending patterns. In their Fig. 1, RR found that the increments of the residual temperature record have Gaussian statistics while the increments of the residual of the solar flare index (SFI) do not and concluded that SWare in error. However, the SFI index measures a daily average of the intensity of the daily solar flare energy output. SW explicitly considered SFI irrelevant for climate change (see Sec. 4B in [3]). SW research focuses [2] on a very different observable: the waiting-time intervals between hard-x-ray flares which are Lévy distributed [7]. The latter record is interpreted as an indicator of the stochastic properties of the solar trending dynamics. So, Gaussian distributed temperature increments create no problem. Because LWs are characterized by the temporal properties of events (not related to their intensity), detrending a LW sequence of its low frequency component destroys its long-trending inferences. Also subsequent research [4–6] further stresses that the link SW found between solar dynamics and climate records must be searched for in the temporal trending (i.e., the smooth) of the signals. Moreover, the temperature trending that RR removes with a fourth-order polynomial fit corresponds to the Gleissberg (50–90 years), Suess (160–260 years), and millenarian solar variability and removing it severely alters the solar signature on the temperature [5]. Figure 1 clarifies the above comments. Panel (a) shows that both long and short solar records share the same scaling exponent of the temperature. Panels (b)–(f) analyze with RR’s smoothing methodology synthetic LW signals mixed with noise, and results equivalent to Fig. 2 in [1] emerge . If the synthetic LW record is detrended of its smooth, the LWmemory is suppressed and random noise scaling ( 1⁄4 H 1⁄4 0:5) is found, which proves that RR’s results are an artifact of their detrending methodology. In conclusion, both RR’s data and methodology are inappropriate for studying a LW signal and testing a solar-climate link as SW did in their work. In any case, a recent publication has shown the existence of a spectral coherence between climate records and astronomical oscillations at multiple time scales that clearly supports a significant solar-climate coupling [6].