Chemistry Climate Model Simulations of Polar Stratospheric Ozone

• Main Author: Brakebusch, Matthias
• Format: Text
• Language: unknown
• Published: CU Scholar 2013
• Subjects: evaluation; model; ozone; polar; quantification; stratosphere; Atmospheric Sciences; Other Oceanography and Atmospheric Sciences and Meteorology; Arctic; Antarctic; The Antarctic; Antarc*
• Online Access: https://scholar.colorado.edu/atoc_gradetds/35; https://scholar.colorado.edu/cgi/viewcontent.cgi?article=1037&context=atoc_gradetds

Stratospheric ozone (O3) plays a crucial role in protecting organisms on Earth from lethal shortwave solar radiation. Because it is radiatively active, O3 also determines the temperature structure of the stratosphere, so its distribution affects the circulation. For these reasons, understanding polar stratospheric O3 has been a high priority of the scientific community for decades. Of primary interest in recent years is explaining and predicting variations in O3 in a changing climate. Stratospheric O3 distributions are affected by both chemistry and transport, which in turn are controlled by temperature, circulation, and dynamics. Hence, investigations of polar stratospheric O3 require the separation of these intertwined processes, and an understanding of the relevant feedbacks. Investigations of these processes require global observations as well as coupled chemistry climate model simulations. This thesis focuses on chemical O3 loss due to halogen and odd nitrogen (NOX) catalytic cycles, and utilizes satellite measurements from several instruments and the Specified Dynamics Whole Atmosphere Community Climate Model (SD-WACCM). The science questions are: (1) Is SD-WACCM a tool sophisticated enough for quantitative O3 evolution investigations? (2) How much O3 loss can be accurately attributed to the stratospheric O3 loss processes induced by halogens, energetic particle precipitation, and NOX individually? (3) Why is the observed O3 in the Arctic 2010/2011 winter exceptionally low, despite high dynamical variability, which is usually associated with less O3 loss? The questions are addressed by: (1) iteratively evaluating and improving SD-WACCM simulations of the Arctic 2004/2005 winter through comparisons with satellite observations; (2) comparing multiple experimental SD-WACCM simulations of the Antarctic 2005 winter omitting individual O3 loss processes to a reference simulation; (3) testing a hypothesis by means of a comprehensive model simulation of the Arctic 2010/11 winter season. Conclusions of this thesis are: (1) SD-WACCM is a useful tool to quantify polar stratospheric O3 evolution after including several model improvements; (2) 74% of total column O3 loss can be attributed robustly to halogen chemistry preceded by heterogeneous chemistry; (3) severe O3 loss in Arctic 2010/11 results in part from enhanced chlorine activation due to the high dynamical variability. The work of this thesis improved SD-WACCM and adds an unprecedented evaluation regarding O3 variability and O3 loss in the stratosphere. Exact quantification of individual O3 loss processes became possible even for extreme seasons. Hence this thesis enables analyses of polar stratospheric winter seasons on a level of detail that was not possible before.