The importance of the representation of stratospheric dynamics and chemistry for surface climate variability
The stratosphere is attracting more and more attention for its potential to improve northern hemisphere (NH) seasonal weather forecasts, by modulating the North Atlantic Oscillation, or for its importance to reproduce observed southern hemisphere (SH) tropospheric jet trends, shaped by stratospheric ozone depletion. However, open questions remain regarding, for example, the stratospheric impact onto the ocean or the extent to which the complexity of stratospheric chemistry is important for surface climate. Within this thesis these two questions shall be answered. The importance of including a full representation of the stratosphere for North Atlantic and North Pacific Ocean variability is investigated for the first time. Furthermore, this thesis investigates the impact of interactive chemistry onto surface climate variability in an unprecedented model study, systematically reducing the complexity of stratospheric chemistry from an interactive chemistry scheme to a specified one prescribing zonal mean as well as zonally asymmetric ozone concentrations. [...] This thesis advances the understanding of the impact of stratospheric dynamics and feedbacks between chemistry and dynamics on surface variability. It concludes that the dynamical representation of the stratosphere is crucial for a more realistic representation of surface variability in the North Atlantic and Pacific Ocean. It underlines the importance of feedbacks betweenchemistry and dynamics for the characteristics of the stratospheric mean state, variability and stratosphere-troposphere-coupling. Especially under a strong ozone forcing, such as the observed Antarctic ozone depletion, incorporating interactive chemistry or at least a zonally asymmetric ozone forcing in a climate model is necessary for a proper representation of surface climate variability.