Decadal variability in the Northern Hemisphere winter circulation: Effects of different solar and terrestrial drivers

https://doi.org/10.1016/j.jastp.2018.06.012Get rights and content
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Highlights

  • Effects of ENSO, volcanic activity, geomagnetic activity and sunspots to winter circulation is studied during 1868-2014.

  • The phase of the QBO is used to study driver signals in different stratospheric conditions during 1900-2014.

  • ENSO and sunspots responses in the Pacific remain the same in different QBO phases supporting direct tropospheric forcing.

  • All driver responses in the Atlantic change notably in different QBO phases supporting substantial stratospheric influence.

Abstract

Northern Hemisphere winter circulation is affected by both solar and terrestrial forcings. El-Niño events and volcanic eruptions have been shown to produce a negative and a positive North Atlantic Oscillation (NAO) signature, respectively. Recent studies show a positive NAO signature related to both geomagnetic activity (proxy for solar wind driven particle precipitation) and sunspot activity (proxy for solar irradiance). Here the relative role of these four different drivers on the Northern Hemisphere wintertime circulation is studied using a statistical analysis of observational and reanalysis data during 1868–2014. The phase of the Quasi-Biennial Oscillation (QBO) is used to study driver signals in different stratospheric conditions. Moreover, the effects are separated for early/mid- and late winter. Our findings suggest a stratospheric mediation of the ENSO signal to the Atlantic side, which is delayed and modulated by the QBO unlike the signal in the Pacific side. The positive NAO by volcanic activity is preferentially obtained in the westerly QBO. We also find a substantial QBO modulation for geomagnetic activity and late winter sunspot activity, which favours a stratospheric pathway and the top-down mechanisms. However, signal in the North Pacific produced by early/mid-winter sunspot activity remain rather similar in different QBO phases and supports a direct forcing from the troposphere by the bottom-up sunspot mechanism.

Keywords

ENSO
Volcanic activity
Solar activity
QBO
Surface circulation
Northern hemisphere winter

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