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Recent studies suggest a response in the North Atlantic winter circulation which lags by a couple of years with respect to sunspot maximum. This has been explained by two different top‐down mechanisms: a solar wind driven particle effect in the polar atmosphere during the declining phase of the solar cycle, and the re‐emergence and amplification of heat anomalies in the Atlantic Ocean produced by enhanced solar ultraviolet (UV). Here we study how December to February climate is affected by two solar‐related drivers: geomagnetic activity (proxy of particle precipitation) and sunspot activity (proxy of solar UV) during 1948–2017. We use reanalysis data of sea‐level pressure (SLP) and zonal wind (U) to show that both geomagnetic activity and sunspot activity independently and simultaneously produce atmospheric circulation responses in the North Atlantic whose evolutions clearly differ from each other. Geomagnetic activity produces a strengthening of the polar vortex and a negative poleward SLP gradient between mid‐ and high latitudes, resembling a positive NAO‐type circulation pattern during December to February. Solar UV produces a positive U anomaly in the low‐latitude stratosphere during December, which moves poleward and downward during the winter resulting in a negative poleward SLP gradient between mid‐ and high latitudes during February. We find the lagged sunspot activity responses in SLP to form zonal pressure patterns (wave‐train structure) resembling the Eurasian pattern. Geomagnetic activity responses remain essentially the same when we introduce the lag with respect to sunspot activity supporting its independency as a driving mechanism. Our results suggest that solar wind related particle precipitation and (lagged) solar UV mechanism provide independent, significant circulation signals in the North Atlantic winter. [ABSTRACT FROM AUTHOR]

Abstract Relation of decadal variations of the North Atlantic Oscillation index (NAOI) to the 11-year solar cycle in the sunspot number is analyzed for almost 200-year observational period with the use of cross-spectral and cross-wavelet techniques. Based on wavelet transforms of a pair of time series, local cross characteristics such as the local coherency and local correlation are used to study time evolution of the solar–NAOI relationship. The analysis of the NAOI is supplemented and confirmed by similar analysis of more than 300-year long data of Central England temperature (CET). Both the solar cycle–NAOI and solar cycle–CET relationships exhibit a quasi-periodic oscillation with the mean period of about 50 years, which includes a subinterval with positive coherency and a subinterval with negative coherency between the solar cycle and the 11-year modes of the NAOI and CET. The same multidecadal modulation of the solar–NAOI relationship is manifested in the temporal structure of the local correlation between the 11-year modes of the NAOI and the sunspot number at specific time lags of the NAOI relative to the sunspot number. It is distinct in the local correlations for the extended winter period (November–March) NAOI lagging by 7 years after the sunspot number. At this lag, the NAOI anticorrelates in general with the sunspot number and the local anticorrelation reinforces periodically with the aforementioned ∼50 year period. At the 1-year lag, which differs from the 7-year lag by a half solar cycle, the 11-year mode of the winter NAOI correlates in general with the solar cycle but the correlation is mainly associated with the last 70-year time interval. The change in the sign of the solar–NAOI relationship is also the case for the extended summer periods of the year (May–September). For this period, the approximately mirror image of the local correlations is observed at the 7-year and 1-year lags. The multidecadal modulation is likely associated with periods of enhanced solar impact on the NAO. Highlights • Relation of the North Atlantic Oscillation index to the solar cycle is modulated. • The mean period of the modulation is about 50 years. • The effect is clearly seen in the 7-year lagged response to the solar cycle. • The modulation is likely associated with multidecadal variations in solar activity. [ABSTRACT FROM AUTHOR]

Numerous studies have suggested an impact of the 11 year solar cycle on the winter North Atlantic Oscillation (NAO), with an increased tendency for positive (negative) NAO signals to occur at maxima (minima) of the solar cycle. Climate models have successfully reproduced this solar cycle modulation of the NAO, although the magnitude of the effect is often considerably weaker than implied by observations. A leading candidate for the mechanism of solar influence is via the impact of ultraviolet radiation variability on heating rates in the tropical upper stratosphere, and consequently on the meridional temperature gradient and zonal winds. Model simulations show a zonal mean wind anomaly that migrates polewards and downwards through wave–mean flow interaction. On reaching the troposphere this produces a response similar to the winter NAO. Recent analyses of observations have shown that solar cycle–NAO link becomes clearer approximately three years after solar maximum and minimum. Previous modelling studies have been unable to reproduce a lagged response of the observed magnitude. In this study, the impact of solar cycle on the NAO is investigated using an atmosphere–ocean coupled climate model. Simulations that include climate forcings are performed over the period 1960–2009 for two solar forcing scenarios: constant solar irradiance, and time-varying solar irradiance. We show that the model produces significant NAO responses peaking several years after extrema of the solar cycle, persisting even when the solar forcing becomes neutral. This confirms suggestions of a further component to the solar influence on the NAO beyond direct atmospheric heating and its dynamical response. Analysis of simulated upper ocean temperature anomalies confirms that the North Atlantic Ocean provides the memory of the solar forcing required to produce the lagged NAO response. These results have implications for improving skill in decadal predictions of the European and North American winter climate.