Impact of the solar cycle and the QBO on the atmosphere and the ocean

The solar cycle and the Quasi-Biennial Oscillation are two major components of natural climate variability. Their direct and indirect influences in the stratosphere and troposphere are subject of a number of studies. The so-called "top-down" mechanism describes how solar UV changes can lead to a significant enhancement of the small initial signal and corresponding changes in stratospheric dynamics. How the signal then propagates to the surface is still under investigation. We continue the "top-down" analysis further down to the ocean and show the dynamical ocean response with respect to the solar cycle and the QBO. For this we use two 110-year chemistry climate model experiments from NCAR's Whole Atmosphere Community Climate Model (WACCM), one with a time varying solar cycle only and one with an additionally nudged QBO, to force an ocean general circulation model, GFZ's Ocean Model for Circulation and Tides (OMCT). We find a significant ocean response to the solar cycle only in combination with a prescribed QBO. Especially in the Southern Hemisphere we find the tendency to positive Southern Annular Mode (SAM) like pattern in the surface pressure and associated wind anomalies during solar maximum conditions. These atmospheric anomalies propagate into the ocean and induce deviations in ocean currents down into deeper layers, inducing an integrated sea surface height signal. Finally, limitations of this study are discussed and it is concluded that comprehensive climate model studies require a middle atmosphere as well as a coupled ocean to investigate and understand natural climate variability.