Modeling and Diagnosis of the Stratospheric Circulation

The transport of chemical species in the stratosphere has major impacts on a variety of ecologically-relevant phenomena. Ozone distributions, for example, reduce incoming ultraviolet solar radiation and thereby increase the viability of life on thesurface of the Earth, whereas water distributions are known to have impacts on the surface radiative balance. These (and other) chemical distributions are often interrelated, such as how water vapor provides the primary source of ozone-destroying hydrogen species in the stratosphere, whereas ozone and water vapor concentrations both play roles in the tropical tropopause radiative balance and thereby affect incoming water vapor mixing ratios. This complexity of interaction presents a challenge in the understanding and modeling of the stratosphere and the transport of chemicals within it. This dissertation presents work which is aimed towards improving both the understanding and modeling of stratospheric transport and is presented in three parts. In the first part, passive tracer transport is used to assess the time scales of stratospheric transport in the absence of non-conserving chemical or other loss processes and in the context of climate model simulations. More particularly, transport timescale distributions are compared between two transport schemes – one Eulerian and the other Lagrangian – which are driven by the same model simulation. The results of this work show that the two transport schemes produce very different transport timescales around many key features of the stratosphere. The Lagrangian model shows slower transport in most of the stratosphere and shows evidence which suggests that it should produce stronger gradients in tracers, in comparison to the Eulerian model, in many locations where strong gradients are expected from observations for a variety of chemical species. In the second part, the modeling experiments from the first part are extended to include water vapor transport. The results of this work show that the Lagrangian model transports much less water vapor into the stratosphere than the Eulerian transport model, particularly in the extratropical lowermost stratosphere. This region shows differences of a factor of two or more (up to five), which raises significant questions about the reliability of current model representations of water vapor in the upper-troposphere lower-stratosphere region and the radiative effects thereof. Furthermore, the water vapor distributions of both transport models were used to drive radiation calculations in two different simulations, for which differences of up to 10 Kelvin in the extratropical lowermost stratosphere were found. [...