🔭 astrophysics

Tidal triggers and the predictability of solar activity

This paper proposes that magneto-Rossby waves in the solar tachocline, synchronized by the combined tidal forcing of Venus, Earth, and Jupiter, drive the quasi-biennial oscillation and the 11-year Schwabe cycle, thereby enabling the prediction of significant solar activity events such as the May 2024 storm and the February 2026 X-flare.

Original authors: F. Stefani, G. M. Horstmann, G. Mamatsashvili, T. Weier

Published 2026-06-02

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CC BY 4.0

Original authors: F. Stefani, G. M. Horstmann, G. Mamatsashvili, T. Weier

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the Sun not just as a burning ball of gas, but as a giant, swirling ocean with its own hidden currents and waves. For a long time, scientists thought the Sun's activity—like its sunspots and massive solar storms—was driven entirely by internal engines. However, this paper suggests a different story: the Sun might be like a giant drum, and the planets orbiting it are the drumsticks, tapping a rhythm that triggers the Sun's most violent outbursts.

Here is the breakdown of the paper's claims in simple terms:

1. The Hidden Waves (The "Ocean" of the Sun)

Deep inside the Sun, there is a layer called the tachocline where the Sun's rotation speeds change. Scientists believe "magneto-Rossby waves" travel through this layer. Think of these like massive, slow-moving ripples in a bathtub. Usually, these ripples are calm, but the paper argues they can be shaken into action by something external.

2. The Planetary Drumsticks (The Tides)

Just as the Moon pulls on Earth's oceans to create tides, the planets Venus, Earth, and Jupiter pull on the Sun. Because these planets orbit at different speeds, they don't always pull at the same time.

Sometimes Venus and Jupiter line up.
Sometimes Earth and Jupiter line up.
Sometimes all three line up.

When they align, their combined gravitational "tug" creates a spring tide on the Sun. The paper calculates that the rhythm created by these planetary alignments produces a specific "beat" or pulse that happens roughly every 1.7 years (about 629 days).

3. The Sun's "Heartbeat" (Predicting Storms)

The researchers looked at two types of extreme solar events:

GLEs: Ground-Level Enhancements (high-energy particles hitting Earth).
S-Flares: Massive solar flares (explosions of energy).

They analyzed 72 GLEs and 37 S-flares recorded over decades. They found a surprising pattern: these solar storms didn't happen randomly. Instead, they tended to occur right when the "planetary drumsticks" hit their strongest beat.

The Analogy: Imagine a row of dominoes. The planets are the hand pushing the first domino. The Sun's internal waves are the line of dominoes. The solar storm is the final domino falling. The paper claims that if you know when the planets align, you can predict when the final domino will fall.

4. The "Sweet Spot" Timing

The paper found that the solar storms don't always happen exactly at the moment of the strongest planetary pull.

The Lag: Sometimes the storm happens a few weeks or even a couple of months after the peak planetary tug.
The Analogy: Think of pushing a child on a swing. You push at the peak of the backward motion, but the child reaches the highest point of the forward motion a moment later. The paper suggests the Sun's internal waves take a little time to build up enough energy to launch a solar storm after the planets give them that initial push.

5. Recent Predictions and "Bugs"

The authors tested their theory against real, recent events:

May 2024: Two solar storms happened.
February 2026: A massive solar flare happened.

The paper claims these events lined up almost perfectly with the predicted peaks of the planetary tides.

Note on a mistake: The authors admit that in a previous attempt to predict the 2026 event, they made a small computer coding error. This caused them to predict the event would happen a month later than it actually did. Once they fixed the math, the prediction matched the reality: the storm happened about 23 days after the peak planetary alignment, which fits their theory of a "lag time."

6. What This Means (According to the Paper)

The paper concludes that:

Solar activity isn't just random chaos; it has a "clock" set by the planets.
The 1.7-year rhythm is a "beat" created by the interaction of Venus, Earth, and Jupiter.
By tracking the positions of these three planets, we might be able to predict when the Sun is most likely to throw a tantrum (a solar storm).

Important Limitation: The authors are careful to say they don't fully understand exactly how the planetary tug turns into a solar storm yet. They know the timing matches, but the physical "engine" connecting the two is still a mystery they are working to solve. They also note that this rhythm works alongside the Sun's famous 11-year cycle, not instead of it.

Technical Summary: Tidal Triggers and the Predictability of Solar Activity

Problem Statement
The paper investigates the potential predictability of extreme solar activity events, specifically Ground-Level Enhancement (GLE) events and S-class superflares, by examining their correlation with tidal forces exerted by planets on the Sun. While magneto-Rossby waves in the solar tachocline are established as a primary determinant of solar activity and the quasi-biennial oscillation (QBO), the specific mechanism triggering these waves and the resulting solar events remains under investigation. Previous work suggested that planetary tides could destabilize neutrally stable Rossby waves, potentially synchronizing the 11-year Schwabe cycle and shorter QBO periods. This study aims to refine the determination of the dominant period governing these events and test the hypothesis that specific planetary alignments (Venus, Earth, and Jupiter) act as tidal triggers for magneto-Rossby waves, thereby influencing the timing of solar storms.

Methodology
The authors analyzed a dataset comprising 72 GLE events (recorded between 1956 and 2025) and 37 S-class flares (soft X-ray events >X10, recorded since 1978). The analysis involved several statistical and theoretical steps:

Period Optimization: The authors calculated correlation coefficients between the timing of solar events and cosine functions with variable periods ( $T_0$ ) and phases ( $\phi_0$ ). They utilized a modified correlation metric, $Corr$, defined as the sum of cosines divided by the square root of the sum of squared cosines, which is conceptually closer to Pearson's correlation coefficient for binary event data.
Theoretical Comparison: The empirically derived best-fit periods were compared against a theoretical period of 629.29 days (1.723 years). This theoretical value represents the dominant beat period resulting from the superposition of spring tides from three planetary pairs: Venus-Jupiter (118 days), Earth-Jupiter (199 days), and Venus-Earth (292 days).
Tidal Signal Modeling: Beyond simple cosine fits, the authors modeled the combined tidal forcing as the sum of three cosine waves ( $s(t)$ ) representing the three planetary pairs. They further analyzed the square of this sum, $s^2(t)$ , hypothesizing that this non-linear term better represents the excitation of tachocline deformations or flux tube launching mechanisms.
Time-Lag Analysis: The correlation between the solar events and the $s^2(t)$ signal (and its moving averages over 101, 201, and 301 days) was assessed with varying time shifts to determine if a physical lag exists between the peak tidal forcing and the occurrence of solar events.
Correction of Previous Errors: The study corrected a timing error and a code bug identified in a previous publication (Stefani et al. 2025), which had previously led to an incorrect phase prediction for early 2026 events.

Key Contributions and Results

Refined Period Determination: The analysis of 72 GLE events yielded an optimal period of 626.67 days (1.716 years) with a correlation coefficient of 0.394. When the period was fixed to the theoretical 629.29 days, the correlation remained high at 0.391. Both results correspond to p-values indicating high statistical significance ( $p \approx 0.0006$ ).
S-Class Flare Correlation: The 37 S-class flares showed even stronger correlations, with coefficients of 0.72 (optimal period 1.747 years) and 0.64 (theoretical period 1.723 years). The p-values for these correlations were exceptionally low ( $5.5 \times 10^{-7}$ and $3.6 \times 10^{-5}$ ).
Combined Dataset: Merging the GLE and S-flare datasets (109 events total) resulted in an optimal period of 632.88 days (1.733 years) and a correlation of 0.435. The theoretical period of 1.723 years yielded a correlation of 0.424, with p-values of $3.2 \times 10^{-6}$ and $6.7 \times 10^{-6}$ , respectively.
Phase Stability: The results confirm that these solar events exhibit phase stability over approximately six solar cycles, aligning with a dominant period very close to the 1.723-year beat of the Venus-Earth-Jupiter tidal system.
Tidal Signal Alignment: The study demonstrated that recent major events, specifically the GLE events of May and June 2024 and the strong X-flare of February 1, 2026, align closely with the peaks or steep gradients of the modeled tidal signal $s^2(t)$ .
Time Lag Observations: While simple cosine fits suggested a near-zero lag, the correlation with the $s^2(t)$ signal and its moving averages showed a maximum correlation at a positive time lag of approximately 70 days (meaning the signal peaks after the events in the raw correlation, or conversely, events occur before the peak in a predictive sense). The authors suggest this may relate to the width of the tidal peaks or the time required for flux tubes to rise to the surface.

Significance and Claims
The paper claims to provide robust statistical evidence supporting the hypothesis that planetary tides, specifically the beat frequencies of the Venus-Earth-Jupiter system, play a role in triggering magneto-Rossby waves in the solar tachocline. This mechanism appears to govern the timing of extreme solar events with a phase-stable period of approximately 1.723 years.

The authors emphasize that the alignment of the 2024 and 2026 solar storms with the theoretical tidal maxima supports the potential for predictability in space weather. However, the paper maintains a modest tone regarding the underlying physics. It acknowledges that while the statistical correlation is significant, the precise physical mechanism linking the tidal excitation of Rossby waves to the actual launching of magnetic flux tubes remains to be fully understood. The authors note that any viable forecast must also account for the phase of the 11-year Schwabe cycle and that other mechanisms cannot be ruled out. The study concludes that future work should focus on refining the weighting of the tidal components based on the instantaneous toroidal field and expanding the dataset to include less extreme events.