The study of global climate and solar activity has long focused on trends, but fluctuations around them often have the same order of magnitude. These strong oscillations have remained a mystery. Neighboring works examine solar cycles, tidal rhythms, and resonances in various systems, but this article unites them through a common nonlinear mechanism. It stands apart: the nearest neighbor is at a distance of 0.531, indicating the novelty of the approach.
The author analyzes instrumental data on global temperature (1880–2009), sea surface temperature (1850–2008), the El Niño index, and sunspot number (1749–2009). To separate the trend, nonlinear nonparametric wavelet regression with a soft VisuShrink threshold is used. Spectra are computed using the maximum entropy method, which provides optimal resolution even for short series. To test for chaos, the largest Lyapunov exponent is calculated, and to identify scaling, structure functions and the autocorrelation defect are used.
In the spectra of detrended global temperature data, a huge peak is found at a period of about three years, with a weak annual peak. This is interpreted as subharmonic resonance at one-third of the frequency of the annual solar forcing. For paleotemperature from Antarctic ice cores (0–340 thousand years), a dominant peak at 15,000 years with a weak peak at 5,000 years also corresponds to a one-third resonance, but now with Earth's precession cycle. In sunspot data, after removing the 11-year trend, a peak at 3.7 years remains, indicating resonance as a background for the 11-year cycle. The spectrum of solar fluctuations shows an exponential decay with a characteristic time of 25.38 days, matching the Sun's rotation period at a latitude of 26 degrees. The largest Lyapunov exponent is positive (0.286 month⁻¹), confirming chaos. Coherence between detrended solar activity and global temperature is high for periods longer than 20 years, although the trends do not correlate.
The work shows that strong fluctuations in climate and solar activity have a common nonlinear nature. Unlike neighboring studies that consider individual cycles or resonances, here a universal mechanism of subharmonic resonance at one-third is proposed. This links heterogeneous systems: from oceanic Rossby waves to the solar dynamo and galactic turbulence. Such an approach could change climate modeling by incorporating nonlinear interactions instead of linear trends.
The topic could develop toward more detailed modeling of nonlinear oscillators with delay for the solar dynamo and climate subsystems. It may be combined with cosmic ray and cloud cover data to test galactic influence. Also promising is the study of subharmonic resonance in other geophysical systems, such as glacial cycles or variations in Earth's magnetic field.
The results will affect climatology, solar physics, and turbulence theory by proposing a unified mechanism to explain fluctuations in these fields.
The next step will be to test the model's predictions on independent data, for example, on temperature reconstructions from other ice cores or on long solar activity records. It is also important to clarify the physical nature of the delay in the solar dynamo and its connection to resonance.
The work directly addresses the unresolved problem of the origin of strong climate fluctuations on different timescales. It shows that nonlinear resonance may be the key to understanding climate variability that linear models cannot explain. This also touches on the problem of climate predictability: if fluctuations are chaotic, long-term forecasts are limited, but their statistical properties can be modeled.
The 3.7-year period found in solar activity coincides with the period of the so-called flip-flop phenomenon: active longitudes on the Sun change dominance roughly every 3.7 years. This points to a common source for both phenomena.
The idea that galactic turbulence influences Earth's climate echoes Isaac Asimov's novel 'The End of Eternity,' where changes in distant space cause cataclysms on Earth.