Speaker
Description
There is growing evidence that solar variability associated with the 11-year sunspot cycle, particularly during solar minima and maxima, influences the troposphere. Numerous observational and modelling studies have linked the solar cycle to winter weather and climate variability in the Euro-Atlantic region. However, the strength of these links remains debated, owing to their reduced stability in extended records, inconsistent detectability across datasets and methodologies, and the seasonally dependent and time-lagged nature of the tropospheric response. Additional uncertainty arises from stratospheric processes, particularly the QBO and sudden stratospheric warmings, which can modulate solar signals through stratosphere– troposphere coupling.
This study investigates the relationship between solar variability and wintertime tropospheric circulation over central Europe by analysing the frequency of synoptic circulation types under different levels of solar activity during 1851–2022, using monthly mean sunspot numbers and the Groswetterlagen reanalysis classification of circulation types. By focusing on circulation- type frequencies, we provide a complementary view of the solar–circulation relationship and assess how solar activity influences tropospheric circulation at smaller temporal and spatial scales.
The results show a significant relationship between solar activity and tropospheric circulation; however, with clear differences between early and late winter. Under low solar activity, westerly types occur less frequently, indicating a suppression of zonal flow, in favour of a higher frequency of northerly types, particularly purely northerly ones. In contrast, under high solar activity, northerly types are significantly reduced, while westerly and south-westerly types are more frequent, predominantly in late winter. Anticyclonic situations occur more frequently under low solar activity, compensating for the reduced frequency of cyclonic types, predominantly in early winter. Finally, the circulation response is stronger during high- intensity solar cycles and weaker during low-intensity cycles.
In summary, solar variability modulates wintertime tropospheric circulation, with a clear subseasonal dependence: the response to low (high) solar activity is strongest in early (late) winter. The magnitude of the circulation response also varies with the amplitude of the solar cycle, and the contrast between early- and late-winter circulation patterns suggests a lagged tropospheric response to the solar signal.