Quantification of the impact of adjusted ozone climatology on a warmer than present climate simulated by AWI-ESM-2.1-LR

christian.stepanek [ at ] awi.de


The existence of ozone as a greenhouse gas in the Earth‘s climate system has a great impact on the radiative transfer in the atmosphere, affecting among others, the global climate. Various climate modelling studies have highlighted the importance of ozone as a key driver of climate change. However, the climate models at the research group, Paleoclimate Dynamics at The Alfred Wegener Institute (AWI) lacked the interactive chemistry scheme for calculating ozone changes due to the enormous computational expenses. In this respect, this thesis addresses the vital question of the accuracy of specific climate patterns in the atmosphere-ocean coupled model AWI-ESM-2.1-LR, in comparison to the behaviour of a real climate state where ozone is fully forcing and reacting to climate changes. Quantification of the adjusted ozone in response to 4xCO2 is crucial, taking into account how modified ozone impacts the climate. In this study, the average values of surface temperature, total precipitation, vertically integrated water vapour, geopotential height at 500 hPa, 250 hPa, 100 hPa levels, and sea ice concentration together with the model metrics like climate sensitivity and polar amplification has been investigated under the aegis of Pre-Industrial (PI), 4xCO2, and 4xCO2_O3 simulations. These simulations have been performed by AWI-ESM-2.1-LR, a state-of-the-art climate model that will be used as a workhorse for simulating various climate states, from much warmer to present, to much colder than present climate states. Noteworthy is the intense Arctic warming during boreal winter in the 4xCO 2 simulation. This pronounced warming can be manifested by the strong increase in vertically integrated water vapour in the Northern Hemisphere (NH) high latitudes. However, the modified ozone forcing on the surface temperature response to 4xCO2 produces a cooling pattern. Furthermore, an enhanced precipitation pattern of 1069.72 mm/year is observed in the tropical mid-latitude region covering parts of South Asia due to a robust land-sea pressure and temperature contrast. The presence of the modified ozone forcing in the 4xCO2_O3 simulation decreases the precipitation to 1056.15 mm/year and causes drying in certain parts of Indonesia, Indian Ocean and Pacific Ocean. Quadrupled carbon dioxide concentration in the 4xCO2 simulation inevitably produces the canonical temperature response driving tropospheric warming due to the steepening of the moist adiabatic lapse rate and stratospheric cooling which enhances the infrared cooling to space by decreasing the upward thermal radiation. Climate Sensitivity (CS), as depicted from the Gregory plot is analysed here as the global surface air temperature change due to a quadrupled carbon dioxide concentration with PI as a reference climate state in the atmosphere and is computed to be 3.43°C, whereas a minor reduction of CS (3.34°C) is noted due to the response of the modified ozone forcing. Defining the Arctic Amplification Index (AAI) from (60-90°N) and (30-60°N), the polar amplification factor is measured as 1.82 with 4xCO2 and PI and 1.79 with 4xCO2_O3 and PI. Overall, the final goal of this thesis is to study the prospective climate impacts of adjusting ozone towards a background climate state. This has been executed by digging deep into the broad pool of data obtained from PI, 4xCO2 simulation together with the third simulation with modified ozone forcing, 4xCO2_O3 , where AWI-ESM-2.1-LR is forced with ozone and computed for 4xCO 2 climate state, by the HadGEM3 model.

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Thesis (Master)
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Helmholtz Cross Cutting Activity (2021-2027)
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Bose, A. (2022): Quantification of the impact of adjusted ozone climatology on a warmer than present climate simulated by AWI-ESM-2.1-LR , Master thesis, Alfred Wegener Institut.

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