Summary
Trends in surface atmospheric variables, namely temperature, wind speed and direction, cloud cover, and precipitation, display subtle patterns that are likely linked to climate change and the major modes of climate variability. In particular, in the Southern hemisphere extra-tropics patterns of variation are strongly impacted by the Sothern Annular Mode (SAM) and the relationships between trends in different variables can also be explained with respect to physical changes linked to SAM. This study aims to examine variations in a range of variables and the relationships between these changes in reanalyses and model output. In particular, we aim to identify whether the patterns of relationships that might be expected a priori based on our underlying knowledge are reproduced in the climate model and also attempt to identify the relative impact of greenhouse gas and stratospheric ozone depletion forcings on these relationships. We will examine the extra-tropical patterns in the trends of a range of atmospheric variables in reanalyses (ERA-interim and MERRA) and derive the underlying relationships between these trends and variability within these measures. We will then complete a similar analysis on the output from a 20th century run of an atmosphere-ocean-chemistry coupled climate model to examine the ability of this model to simulate the observed trends and importantly their interdependencies. We will then compare the trends and their relationships in the Southern hemisphere extra-tropics for runs which include and neglect ozone forcings. We hope that this will allow us to identify the relative importance of greenhouse gas and stratospheric ozone depletion forcings on the patterns observed and their relationships providing a more holistic analysis than previously considered.
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