Investigating stratospheric ozone change and associated impacts on circulation and climate

• Main Author: Stone, Kane
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: 2015
• Subjects: ozone; stratosphere; Dobson; Umkehr; climate; circulation; Southern Hemisphere; chemistry climate model; chemistry; atmospheric chemistry; climate modelling; zonal waves; zonal asymmetry; tropopause; ozone depleting substances; greenhouse gases; ozone recovery; ozone hole; ozone depletion; Antarctic; Kane; South Pole; Antarc*; South pole
• Online Access: http://hdl.handle.net/11343/91558

© 2015 Dr. Kane Adam Stone With stratospheric ozone on the path to recovery, understanding its future role in modulating Southern Hemisphere circulation and climate is essential. This work contributes to answering this question through both observational and modelling studies. First, a new Dobson Umkehr retrieval technique optimised for resolution was developed, with the retrievals contributing in the evaluation of the Australian Community Climate and Earth-System Simulator-Chemistry Climate Model (ACCESS- CCM). This model was used to investigate future Southern Hemisphere stratospheric ozone changes and associated dynamical and climate responses, particularly in the Southern Annular Mode (SAM), the tropopause height and quasi-stationary waves. For this purpose, four simulations were completed comprising of historical, future projection and sensitivity simulations with fixed ozone depleting substances and greenhouse gases (GHGs) at 1960 levels. These simulations also act as Australia’s contribution to the international Chemistry Climate Model Initiative. The Dobson Umkehr retrieval technique developed here uses all available data, unlike other algorithms, which use designated solar zenith angles (SZAs) from a single wavelength pair (C), out of three (A, C and D). Investigating a test case from Melbourne, the degrees of freedom for signal increased from 3.1 to 3.4 when using all C-pair SZAs, and up to 6.5 when using all available SZAs and wavelength pairs; a significant improvement over current operational methods. ACCESS-CCM evaluation shows excessive ozone but an accurate distribution, and a temporally persistent ozone hole. Comparison with the Dobson Umkehr retrievals, total column ozone observations, ERA-Interim reanalysis and past modelling studies shows ACCESS-CCM produces excess ozone at altitudes above 25 km for Melbourne, but with substantial improvements in Antarctic total column ozone over it’s precursors (CCMVal-2 UMUKCA models). Comparisons with Davis and South Pole ozonesondes display a large disparity in the vertical location of perturbed ozone. Maximum depletion is seen between 100–50 hPa in ozonesondes, compared to above 50 hPa in ACCESS-CCM. This difference is likely caused by cold model biases enhancing polar stratospheric cloud formation and subsequent chlorine release at high altitudes. The lack of supercooled ternary solution may be a cause of less depletion between 100–50 hPa. Despite these inadequacies, ACCESS-CCM is simulating the amount of historical Antarctic October ozone depletion, the SAM and 50 hPa zonal wind anomalies well compared to ERA-Interim and past modelling studies. This gives confidence that the model simulates reasonable ozone-induced circulation responses. The model shows that October averaged Antarctic ozone is returning to 1980 levels just after 2060. Increasing GHG and ozone concentrations act to delay and advance the breakup of the polar vortex respectively. Regression analysis shows that in the future, increasing GHGs and ozone concentrations drive an increase and decrease in the SAM index respectively, effectively cancelling each other out. Contrary to the SAM, the high latitude tropopause changes, while influenced heavily by ozone changes in the past, is dominated by increasing GHGs in the future. The phase of spring and summer wave 1 in TCO, 50hPa temperature and 10hPa zonal wind undergo an eastward shift due to both ozone depletion and GHG increases. The wave 1 phase influence from GHGs is seen to originate from the troposphere, and therefore is influenced heavily by Andes orography. This is not the case for ozone concentration changes, indicating that the main influence is through modulation of the stratospheric polar vortex. A decrease in the amplitude is also seen due to GHG increases, primarily due to a decrease in the amplitude of the tropospheric wave 1.