Summary
Links between changes in the southern polar stratosphere and tropospheric climate have been identified in both modelling and observational studies, highlighting the importance of an accurate stratosphere in climate models. However, the model background temperature structure in the winter polar stratosphere is often biased: “the cold pole problem”. In the absence of direct radiative heating through much of this time, it is dynamics that sets the thermal state of this part of the atmosphere through wave--driven meridional and vertical circulations. Hemispheric differences in the manifestation of this problem point to a different balance between large scale waves (which are naturally represented in models) and gravity waves whose scales are of the order of model grid sizes (and are not naturally represented). It is apparent that our ability to predict southern hemisphere stratospheric responses to changing dynamics depends on the correct parameterization of gravity waves. A review of gravity wave drag parameterization schemes will show that these schemes are generally non--physical and often use a prescribed source distribution. The vertical propagation of their influence also lacks a physical basis but points to a key factor in the development of new schemes; they must be computationally efficient if widespread uptake is to be realised. Some gravity wave theory, and observations that are planned to place constraint the physics of these schemes, will be interpreted in the light of parallel modelling constraints.
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