Stratospheric ozone and Southern Hemisphere climate change:impacts and robustness in CMIP5 models

• Main Author: Sanderson, Helen
• Format: Thesis
• Language: English
• Published: Lancaster University 2016
• Subjects: Austral; Antarc*; Antarctica
• Online Access: https://eprints.lancs.ac.uk/id/eprint/80196/; https://eprints.lancs.ac.uk/id/eprint/80196/1/2016sandersonMSc.pdf

Stratospheric ozone depletion is thought to be the dominant cause of recent observed southern hemisphere (SH) circulation changes during austral summer, along with the consequential impacts on tropospheric climate conditions. Links between ozone depletion and the positive phase of the dominant mode of variability of the southern annular mode (SAM) have been found, which in turn are linked to changes in precipitation, atmospheric temperatures and winds. This dissertation investigates how well the models from the most recent Coupled Model Intercomparison Project (CMIP5) represent these changes and searches for consistencies and differences across the models. Comparisons are made with the reanalysis data set ERA-Interim. It is found that the magnitudes of the model trends vary dramatically across the CMIP5 ensemble, although between 1960-2000 all models have decreasing austral spring stratospheric ozone and November temperatures and increasing austral summer SAM trends. Across the CMIP5 models, the strength of the SAM trend is only loosely related to the strength of the stratospheric ozone trend, and this relationship does not always hold. There are changes in precipitation and surface temperatures that are significantly related to the SAM, with bands of increasing and decreasing trends across the SH, likely as a result of the poleward shift in storm tracks. However the magnitude and location of regional changes in surface climate that can be attributed to the SAM differ considerably across the models. For correlations of the SAM with both precipitation and surface temperatures, the models underestimate the correlation over southern Africa and are relatively good representations of Antarctica when compared to reanalysis data.