Courtillot, 2021 presents compelling evidence that planetary dynamics can materially influence the solar radiance. The sharpened decline of solar activity since 1990 is evident in sun spot data:
Finding whether the planets of the solar system, and in particular the Jovian planets, have an influence on planet Earth is currently undergoing a revival and has become the focus of renewed attention. The present paper deals with the prediction of the starting solar activity cycle, Solar Cycle 25. We propose that astronomical ephemeris, specifically the catalogs of aphelia of the four Jovian planets, can be used as evidence of a driving mechanism of variations in solar activity, represented by the series of sunspot numbers SSN from 1749 to 2020 (Appendix B). We use singular spectrum analysis (SSA) to associate components with similar periods in the ephemeris and SSN. We determine the transfer function between the two data sets, first with Jupiter only, then we improve the match in steps with the four Jovian planets and finally including commensurable periods of pairs and pairs of pairs of the Jovian planets (following for instance Mörth and Schlamminger 1979). The transfer function can be applied to the ephemeris to predict future values of cycles. We have tested this with success with the hindcast of Solar Cycles 21 to 24 using only data preceding these cycles. We have also divided the full data set into two halves. Using the SSA method applied to Solar Cycles 1 to 13, we successfully “predict” the characteristics of Solar Cycle 14. Then, we use the second half of the SSN data (from Solar Cycle 14 to 24) to obtain another “prediction” of Solar Cycle 25. The shorter time series used results in (unacceptable) negative SSN values. This is interpreted as a failure to extract a proper trend from too short a data set, which does not allow a correct interpretation of the trend, as a result of ephemeris periods longer than the data interval of the truncated SSN series. But the trend is correctly recovered when the full-length series is used and the effect of the ephemeris of Uranus and Saturn is recognized. Figures 7 and 11 demonstrate the quality of the SSA model when one computes the sum of the SSA components with periods compatible with the revolution periods of Jovian planets and the periodicities of the ephemeris of commensurable pairs Jupiter/Saturn and Uranus/Neptune and pair of pairs (Jupiter/Saturn)/(Uranus/Neptune).
We conclude with a prediction of Solar Cycle 25 that can be compared to a dozen predictions by other authors (Petrovay 2020): the maximum would occur in 2026.2 (± 1 yr) and reach an amplitude of 97.6 (± 10), similar to that of Solar Cycle 24, therefore sketching a new “Modern minimum”, following the Dalton and Gleissberg minima in the previous 200 years.
Although the exact mechanism for this influence of planets on the fluid envelopes of the Sun (photosphere) and also Earth (atmosphere and ocean) is still not fully understood, this influence is clearly apparent in the present paper. We have seen that for instance the long period trend that we extract with SSA in a time window of 200 years could in part be the signature of a long period ephemeris, such as periods linked to Neptune (165 yr; Table 1). We could include the terrestrial planets but expect smaller contributions (these could for instance have a bearing on features such as double maxima). In closing, we wish to emphasize the fact that the powerful SSA method of analysis of quasi-periodic oscillations is a central tool in this analysis. The reconstructed transfer functions that allow one to pass from the ephemeris to the sunspots should be applicable as long as the source (astronomical ephemeris) will stand and as long as we have included all effects from the relevant planets. The SSA reconstruction we propose can be used to predict beyond Solar Cycle 25, but may be degraded with time since oscillations longer than the data interval may have been missed.
Hajra, 2021 reports the solar minimum now in process will be the weakest – a finding consistent with recent evidence of planetary cooling:
The present work indicates a strong impact of the solar activity cycle magnitude on the solar wind–magnetosphere energy coupling and resultant geomagnetic activity. The weakest magnitude of Solar Cycle 24 is found to be associated with an overall reduction in energy coupling and reduced numbers of magnetic storms and HILDCAAs. The stronger the storms, the stronger the reduction in number with no superstorms in Solar Cycle 24. This has a great impact on the cosmic ray shielding. As shown in the present work, reduced solar activity makes the near-Earth space exposed to a higher flux of cosmic rays. This can have important effects on manned missions at low Earth orbit or to the Moon and Mars.
Recent studies predict the solar activity entering in a period of grand minimum (e.g. Wang, 2017; Jiang and Cao, 2018; Upton and Hathaway, 2018; Gonçalves, Echer, and Frigo, 2020, and references therein). This may lead to a much lower solar wind energy input in the magnetosphere and a further decrease in geomagnetic activity events. This has large impacts on space weather effects and technological applications.
Kossobokov et al., 2010 presented empirical evidence of localized cooling in 3 major European cities:
A consequence of our study is that numerical values of sensitivities or any parameter linking solar activity (energy input as a function of wavelength) or increase in GHGs to climate response (temperatures, in particular) may need to be revised (Miura et al., 2005; Chylek et al., 2007; Easterling and Wehner, 2009). There is actually growing evidence of a significant influence of solar activity (TSI) on climate (temperatures, in particular), which is not fully captured in model predictions (Scafetta and West, 2007; Camp and Tung, 2007). The effect may be larger than inferred from the very small changes in TSI observed over the past three solar cycles by satellites (Foukal et al., 2006; Fröhlich, 2006). Moreover, the uncertainty in closing the so-called ACRIM-gap may change our understanding of the relative significance of TSI variations among other forcing factors of climate change (Scafetta and Willson, 2009). These authors conclude that “This finding has evident repercussions for climate change and solar physics. Increasing TSI between 1980–2000 could have contributed significantly to global warming during the last three decades (Scafetta and West, 2007, Scafetta and West, 2008). Current climate models (Intergovernmental Panel on Climate Change, 2007) have assumed that the TSI did not vary significantly during the last 30 years and have therefore underestimated the solar contribution and overestimated the anthropogenic contribution to global warming”. However, this analysis is disputed by Krivova et al. (2009), who find a decrease not an increase of solar activity between the solar minima of 1986 and 1996 (with the most recent minimum being still lower, the total amplitude of long-term TSI variation being on the order of 1 W m−2).
Having found regularities in the past behavior of the Sun, de Jager (2008) suggests that it is undergoing a transition to a lower energy state. This author discusses heliospheric drivers of Sun–climate interactions and finds that about one half of the Sun’s equatorial magnetic fields and one third of the Sun’s polar fields contribute to tropospheric temperatures. De Jager (2008) finds that “the recent global warming peak does not seem to differ significantly from the other peaks that occurred during the last four centuries. (…) As such, the recent period of global warming does not appear to be exceptional from a historical perspective”.
Courtillot, V., Lopes, F., & Le Mouël, J. L. (2021). On the prediction of Solar Cycles. Solar Physics, 296(1). doi:10.1007/s11207-020-01760-7
Hajra, R. (2021). Weakest solar cycle of the space age: A study on solar wind–magnetosphere energy coupling and geomagnetic activity. Solar Physics, 296(2). doi:10.1007/s11207-021-01774-9
Kossobokov, V., Le Mouël, J.-L., & Courtillot, V. (2010). A statistically significant signature of multi-decadal solar activity changes in atmospheric temperatures at three European stations. Journal of Atmospheric and Solar-Terrestrial Physics, 72(7–8), 595–606.