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Introduction

        A quantitative understanding of the influence of solar ul- traviolet variability on the stratosphere-troposphere system re- quires both observations of the atmospheric response and the development of detailed physical models that explain that re- sponse. On the time scale of the 27-day solar rotation pe- riod, such an understanding has been partially achieved, at least in the case of the observed response of ozone at low latitudes [1,2]. However, on the time scale of the 11-year solar cycle, there are large differences between the observed stratospheric response and that which is predicted by existing models. Some of this difference may be a result of measure- ment inaccuracies; however, a significant part of the difference appears to be a result of model deficiencies. In this paper, the observed characteristics of the 11-year stratospheric response are first summarized, based mainly on satellite measurements of stratospheric temperature and ozone. Emphasis is placed on annually averaged measurements at low to middle latitudes. Comparisons are made with the predictions of a current gen- eral circulation model [3] to illustrate the differences between available models and observations. Possible mechanisms for explaining these differences are then discussed.