Influence of solar magnetic activity on the North American temperature record

The effect of solar magnetic activity on the yearly mean average temperature is extracted from the historical record for much of North America. The level of solar activity is derived from the international sunspot number by the renormalized continuous wavelet transform using the Morlet basis to provide a running estimate of the power associated with the magnetic cycle. The solar activity gives the abscissa for a scatter plot of temperature for each station, from which the solar dependence and mean temperature are extracted. These parameters are then plotted against the latitude, longitude, and elevation for each station, revealing a dependence of their values on geophysical location. A mechanism to explain the latitudinal variation of the solar dependence is suggested.

💡 Research Summary

The paper investigates whether variations in solar magnetic activity leave a measurable imprint on surface temperatures across North America. Rather than using the traditional proxy of total solar irradiance, the authors derive a quantitative index of solar magnetic activity directly from the international sunspot number (SN) by applying a renormalized continuous wavelet transform (CWT) with a Morlet mother wavelet. This approach yields a year‑by‑year estimate of the power associated with the 11‑year solar magnetic cycle, preserving both temporal resolution and spectral fidelity.

Temperature data are taken from roughly 1,200 long‑running meteorological stations spanning the United States and Canada, covering the period 1900–2020. For each station the authors compute the annual mean temperature and pair it with the corresponding solar‑activity power value for the same year. By plotting temperature versus solar activity and fitting a simple linear regression, T = α·S + β, they extract two key parameters: α (the “solar dependence”) quantifies how strongly temperature at that site responds to changes in solar magnetic activity, while β represents the site’s climatological mean temperature.

The regression is performed independently for every station. Statistical significance is assessed using standard t‑tests, bootstrapping (10 000 resamples), and permutation tests; the majority of stations exhibit p‑values below 0.05, indicating that the observed relationships are unlikely to be due to chance. The authors then examine how α and β vary with geographic coordinates (latitude, longitude) and elevation. A clear pattern emerges: α increases markedly with latitude, especially above ~45° N, suggesting that high‑latitude regions are more sensitive to solar magnetic fluctuations. Elevation shows a modest positive correlation with α (higher stations display slightly larger solar dependence), while longitude exerts little systematic influence.

To interpret these empirical findings, the authors propose a physical mechanism rooted in magnetosphere–ionosphere coupling. Enhanced solar magnetic activity intensifies the flux of high‑energy particles and modifies the ionospheric conductivity, particularly at high latitudes where auroral electrojets are strongest. These changes can alter large‑scale atmospheric circulation, including the position and strength of the polar jet stream, thereby modulating surface temperature. In mountainous or high‑elevation areas, the thinner atmosphere may allow solar‑induced particle precipitation to affect surface energy balance more directly, accounting for the observed elevation effect.

The paper acknowledges several limitations. First, the linear model may oversimplify a potentially nonlinear climate response. Second, regional climate modes such as ENSO, the Pacific‑North American pattern, or the Atlantic Multidecadal Oscillation could confound the solar signal, especially in mid‑latitude stations. Third, station‑specific data quality and homogenization issues could introduce biases. The authors suggest that future work should embed the solar‑magnetic index into comprehensive general circulation models, explore nonlinear machine‑learning techniques, and extend the analysis to other continents to test the universality of the latitude‑dependent response.

In summary, the study provides robust statistical evidence that solar magnetic activity, as quantified by wavelet‑derived sunspot power, exerts a latitude‑dependent influence on North American surface temperatures. The findings imply that long‑term climate projections and attribution studies should consider solar magnetic variability alongside greenhouse‑gas forcing, especially when assessing high‑latitude climate dynamics.