Stratospheric Responses to the 11-year Solar Cycle in MAECHAM5 with and without Ocean Coupling

Abstract

The current generation of general circulation models (GCMs) faces major difficulties in reproducing, both qualitatively and quantitatively, the observed stratospheric response to the 11-year solar cycle. Because the majority of the previous studies used atmosphere-only GCMs without ocean coupling, it has been suggested that the inclusion of ocean dynamics may improve the simulated solar cycle signals. Our ensemble simulations with a coupled atmosphere-ocean GCM shows no indication that the ocean coupling alters significantly the solar cycle signals in the stratosphere. Although a measurable warming in the tropical oceans during solar maxima is detected in the coupled ensemble, its amplitude is too weak to affect the stratosphere. As such, the simulated temperature and zonal-mean zonal wind changes in the stratosphere are qualitatively similar both in the coupled and uncoupled ensembles. The simulated tropospheric response to the solar cycle forcing, however, differs significantly between the ensemble with and without ocean coupling.