Oscillations of the baseline of solar magnetic field and solar irradiance on a millennial timescale (2002.06550v3)

Abstract: Recently discovered long-term oscillations of the solar background magnetic field associated with double dynamo waves generated in inner and outer layers of the Sun indicate that the solar activity is heading in the next three decades (2019-2055) to a Modern grand minimum similar to Maunder one. On the other hand, a reconstruction of solar total irradiance suggests that since the Maunder minimum there is an increase in the cycle-averaged total solar irradiance (TSI) by a value of about $1-1.5$ $Wm^{-2}$ closely correlated with an increase of the baseline (average) terrestrial temperature. In order to understand these two opposite trends, we calculated the double dynamo summary curve of magnetic field variations backward one hundred thousand years allowing us to confirm strong oscillations of solar activity in regular (11 year) and recently reported grand (350-400 year) solar cycles caused by actions of the double solar dynamo. In addition, oscillations of the baseline (zero-line) of magnetic field with a period of $1950\pm95$ years (a super-grand cycle) are discovered by applying a running averaging filter to suppress large-scale oscillations of 11 year cycles. Latest minimum of the baseline oscillations is found to coincide with the grand solar minimum (the Maunder minimum) occurred before the current super-grand cycle start. Since then the baseline magnitude became slowly increasing towards its maximum at $~$2700 to be followed by its decrease and minimum at $~$3700. These oscillations of the baseline solar magnetic field are found associated with a long-term solar inertial motion about the barycenter of the solar system that can lead to a further natural increase of the terrestrial temperature by 2.5-3.0$^\circ$C.

• The paper identifies long-term solar magnetic field oscillations and super-grand cycles using a double dynamo model and predicts a modern grand minimum.
• Principal Component Analysis was applied to solar magnetograms to identify oscillations linked to a double dynamo mechanism, used to build a summary curve for predictions.
• Implications suggest solar activity influences long-term terrestrial climate patterns and underscore the importance of integrating solar cycles into future climate models by researchers and professionals.

Overview of Solar Magnetic Field Oscillations and Implications on Terrestrial Climate

The paper, authored by Zharkova, Shepherd, and Popova, presents an in-depth analysis of solar magnetic field oscillations over millennial timescales, with a significant focus on understanding potential terrestrial impacts. Employing the novel identification of double dynamo waves, the authors explore complex interactions within the solar interior, offering novel predictions concerning future solar activity and its implications for Earth's climate.

Key Findings

The paper uncovers long-term oscillations of the solar background magnetic field, linked to double dynamo waves generated in the Sun's inner and outer layers. It posits that solar activity is inclining toward a modern grand minimum within the next few decades, akin to the historically known Maunder Minimum. These findings are grounded in a reconstruction of the solar total irradiance (TSI), indicating an increase in TSI since the Maunder Minimum by approximately 1-1.5 W/m$^2$, correlated with a rise in terrestrial temperatures.

The paper extends the double dynamo summary curve of magnetic field variations back 100,000 years, confirming significant oscillations in both regular (11-year) and grand solar cycles (350-400 years). Notably, super-grand cycles of approximately 1950 years were identified using a running averaging filter, providing insight into periods characterized by low-level solar activity such as the Maunder Minimum.

Methodology

Principal Component Analysis (PCA) applied to the low-resolution full disk magnetograms from cycles 21 to 23 was pivotal in revealing two principal components associated with solar magnetic oscillations. These are linked to magnetic waves generated by a double dynamo mechanism in separate solar interior layers. The paper constructs a summary curve from these waves, resembling well-documented historical sunspot activity and terrestrial climatic events.

Theoretical and Practical Implications

The described solar magnetic field oscillations have far-reaching implications for understanding long-term climate patterns on Earth. The paper relates solar activity to the Earth's climate, suggesting that ongoing changes in solar activity patterns align with historical climate variations, such as the medieval and Roman warm periods.

The prediction model derived from the summary curve indicates a potential natural increase in terrestrial temperature by approximately 2.5°C over the next five centuries, attributed in part to solar inertial motion and its effect on solar irradiance. This highlights solar activity's role in shaping Earth's climate over extended periods and underscores the importance of accounting for such natural cycles in climate modeling.

Future Directions and Research

The paper opens pathways for future research into the interaction between solar dynamo models and planetary motions, paving the way for improved predictive models of solar and terrestrial climate interactions. An intriguing aspect of the ongoing paper involves investigating the solar inertial motion around the barycenter of the solar system and its subtle influences on solar-terrestrial dynamics. Understanding these interactions could refine predictions of long-term climate trends, integrating both human-induced and natural factors into climate models.

In conclusion, while the paper offers significant contributions to the field of solar physics and climatology, it also suggests the necessity for integrated-model approaches that encompass solar and planetary influences alongside anthropogenic factors. The insights provided by this work have the potential to enhance predictive climate models by incorporating long-term solar cycles, a critical step in the scientific interrogation of climate variability and change.