Delayed North Atlantic Response to Solar Forcing of the Stratospheric Polar Vortex

Abstract

A delayed response of the winter North Atlantic oscillation (NAO) to the 11-year solar cycle has been observed and modeled in recent studies. However, the mechanisms creating this 2−4- year delay to the solar cycle have still not been well-understood. This study examines the effects of the 11-year solar cycle and the resulting modulation in the strength of the winter stratospheric polar vortex. A coupled atmosphere–ocean general circulation model is used to simulate these effects by introducing a mechanis- tic forcing in the stratosphere. The intensified stratospheric polar vortex is shown to induce positive and negative ocean temperature anomalies in the North Atlantic Ocean. The positive ocean tem- perature anomaly migrated northward and was amplified when it approached an oceanic frontal zone approximately 3 years after the forcing became maximum. This delayed ocean response is similar to that observed. The result of this study supports a previ- ous hypothesis that suggests that the 11-year solar cycle signals on the Earth’s surface are produced through a downward penetration of the changes in the stratospheric circulation. Furthermore, the spatial structure of the signal is modulated by its interaction with the ocean circulation.