Exploring the stratospheric/tropospheric response to solar forcing

We use the new Goddard Institute for Space Studies Global Climate Middle Atmosphere Model 3 with four different resolutions to investigate various aspects of solar cycle influence on the troposphere/stratosphere system. Three different configurations of sea surface temperatures are used to help determine whether the tropospheric response is due to forcing from above (UV variations impacting the stratosphere) or below (total solar irradiance changes acting through the surface temperature field). The results show that the stratospheric response is highly repeatable and significant. With the more active sun, the annual residual circulation change features relative increased upwelling in the Southern Hemisphere and downwelling in the Northern Hemisphere. Stratospheric west wind increases extend down into the troposphere, especially during Southern Hemisphere winter, and in some runs the jet stream weakens and moves poleward. The predominant tropospheric response consists of warming in the troposphere, with precipitation decreases south of the equator and in the Northern Hemisphere subtropics and midlatitudes, with increases north of the equator especially over southern Asia. The tropospheric response is often not significant, but is fairly robust among the different simulations. These features, which have been reported in observations and other model studies, appear to be driven both from the stratosphere and the surface; nevertheless, they account for only a small percentage of the total variance. More accurate simulations of the solar cycle stratospheric ozone response, the quasi-biennial oscillation, and coupled atmosphere-ocean dynamics are necessary before any conclusions can be deemed definitive.