Low-Frequency Stratospheric Variability and its Link to Surface Climate: Insights from Reanalysis and Multi-Century Coupled Climate Model Simulations

Abstract. The Northern Hemisphere stratosphere exhibits variability across subseasonal to multi-decadal timescales. While subseasonal-to-seasonal stratospheric variations have been shown to link to surface climate variability, low-frequency stratospheric variability and its coupling to the surface remain less well understood due to the short observational record and model limitations in simulating variability on these timescales. Here, we analyze low-frequency stratospheric variability using the CERA-20C Reanalysis, and multi-century simulations from three fully coupled models: CESM2.0-WACCM, CESM1.0-CAM4 and CESM2.0-CAM6. We identify an oscillatory stratospheric variability with a ∼15-year period that is consistently present across reanalysis and all three models. Wavelet analysis suggests that this ∼15-year periodicity is highly non-stationary and intermittent owing to the coexistence of other periodic variability on longer timescales. The ∼15-year frequency peak in stratospheric variability is closely associated with the North Atlantic Oscillation (NAO) and tends to lead NAO surface variability. Although all models simulate the stratospheric ∼15-year peak to some degree, they differ in simulating the link between this frequency peak and the surface NAO: WACCM shows the closest agreement with reanalysis, whereas CAM4 demonstrates limited capability in simulating low-frequency stratosphere-NAO coupling, and CAM6 again exhibits closer agreement with reanalysis. By contrast, the relationship between the stratospheric ∼15-year variability and the Aleutian Low is comparatively weak and less consistent across the reanalysis and models. These results help improve our understanding of how low-frequency stratospheric variability is connected to surface variability.