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  • 1
    Call number: AWI A5-24-95744
    Description / Table of Contents: The Arctic is the hot spot of the ongoing, global climate change. Over the last decades, near-surface temperatures in the Arctic have been rising almost four times faster than on global average. This amplified warming of the Arctic and the associated rapid changes of its environment are largely influenced by interactions between individual components of the Arctic climate system. On daily to weekly time scales, storms can have major impacts on the Arctic sea-ice cover and are thus an important part of these interactions within the Arctic climate. The sea-ice impacts of storms are related to high wind speeds, which enhance the drift and deformation of sea ice, as well as to changes in the surface energy budget in association with air mass advection, which impact the seasonal sea-ice growth and melt. The occurrence of storms in the Arctic is typically associated with the passage of transient cyclones. Even though the above described mechanisms how storms/cyclones impact the Arctic sea ice are in principal known, there is a lack of statistical quantification of these effects. In accordance with that, the overarching objective of this thesis is to statistically quantify cyclone impacts on sea-ice concentration (SIC) in the Atlantic Arctic Ocean over the last four decades. In order to further advance the understanding of the related mechanisms, an additional objective is to separate dynamic and thermodynamic cyclone impacts on sea ice and assess their relative importance. Finally, this thesis aims to quantify recent changes in cyclone impacts on SIC. These research objectives are tackled utilizing various data sets, including atmospheric and oceanic reanalysis data as well as a coupled model simulation and a cyclone tracking algorithm. Results from this thesis demonstrate that cyclones are significantly impacting SIC in the Atlantic Arctic Ocean from autumn to spring, while there are mostly no significant impacts in summer. The strength and the sign (SIC decreasing or SIC increasing) of the cyclone impacts strongly depends on the considered daily time scale and the region of the Atlantic Arctic Ocean. Specifically, an initial decrease in SIC (day -3 to day 0 relative to the cyclone) is found in the Greenland, Barents and Kara Seas, while SIC increases following cyclones (day 0 to day 5 relative to the cyclone) are mostly limited to the Barents and Kara Seas. For the cold season, this results in a pronounced regional difference between overall (day -3 to day 5 relative to the cyclone) SIC-decreasing cyclone impacts in the Greenland Sea and overall SIC-increasing cyclone impacts in the Barents and Kara Seas. A cyclone case study based on a coupled model simulation indicates that both dynamic and thermodynamic mechanisms contribute to cyclone impacts on sea ice in winter. A typical pattern consisting of an initial dominance of dynamic sea-ice changes followed by enhanced thermodynamic ice growth after the cyclone passage was found. This enhanced ice growth after the cyclone passage most likely also explains the (statistical) overall SIC-increasing effects of cyclones in the Barents and Kara Seas in the cold season. Significant changes in cyclone impacts on SIC over the last four decades have emerged throughout the year. These recent changes are strongly varying from region to region and month to month. The strongest trends in cyclone impacts on SIC are found in autumn in the Barents and Kara Seas. Here, the magnitude of destructive cyclone impacts on SIC has approximately doubled over the last four decades. The SIC-increasing effects following the cyclone passage have particularly weakened in the Barents Sea in autumn. As a consequence, previously existing overall SIC-increasing cyclone impacts in this region in autumn have recently disappeared. Generally, results from this thesis show that changes in the state of the sea-ice cover (decrease in mean sea-ice concentration and thickness) and near-surface air temperature are most important for changed cyclone impacts on SIC, while changes in cyclone properties (i.e. intensity) do not play a significant role.
    Type of Medium: Dissertations
    Pages: VIII, 131 Seiten , Illustrationen, Diagramme
    Language: English
    Note: Dissertation, Universität Potsdam, 2024 , Contents 1 Introduction 1.1 The Arctic sea-ice cover 1.1.1 Sea ice in the coupled Arctic climate system 1.1.2 Recent changes of the Arctic sea ice 1.2 The atmosphere as driver of sea-ice variability 1.2.1 Large-scale circulation patterns 1.2.2 Role of cyclones 1.3 Thesis structure and research questions 2 Theory and methods 2.1 Synoptic cyclones 2.1.1 Related fundamentals of atmospheric dynamics 2.1.2 Cyclone activity in the Arctic 2.2 Cyclone tracking and cyclone occurrence mask 2.3 Dynamic and thermodynamic sea-ice variability related to cyclones 3 New insights into cyclone impacts on sea ice in the Atlantic sector of the Arctic Ocean in winter 3.1 Abstract 3.2 Introduction 3.3 Data and methods 3.3.1 Database and cyclone identification 3.3.2 Quantification of cyclone impacts on SIC 3.4 Cyclone impacts on SIC 3.4.1 Effects of different time scales and regions 3.4.2 Effects of SIC conditions and cyclone depth 3.4.3 Spatial variability of SIC response to cyclones 3.4.4 Relation to near-surface wind and surface energy budget 3.5 Signature of ’New Arctic’ conditions 3.6 Conclusions 3.7 Supplementary material 4 Impact of three intense winter cyclones on the sea ice cover in the Barents Sea: A case study with a coupled regional climate model 4.1 Abstract 4.2 Introduction 4.3 Data and methods 4.3.1 HIRHAM–NAOSIM simulation 4.3.2 Supplementary evaluation data 4.3.3 Dynamic and thermodynamic contributions to sea-ice changes 4.4 Results 4.4.1 Cyclone cases 4.4.2 Cyclone impacts on SEB 4.4.3 Cyclone impacts on sea-ice concentration (SIC) 4.4.4 Cyclone impacts on sea-ice thickness (SIT) 4.4.5 Context to other cyclone cases during the MOSAiC winter 4.5 Discussion and conclusions 4.6 Supplementary material 5 Cyclone impacts on sea ice concentration in the Atlantic Arctic Ocean: Annual cycle and recent changes 5.1 Abstract 5.2 Introduction 5.3 Data and methods 5.4 Changes in cyclones and traversed sea ice 5.5 Cyclone impacts on SIC 5.5.1 Annual cycle in the old Arctic 5.5.2 Changes in the new Arctic 5.5.3 Regional changes in autumn 5.6 Conclusions 5.7 Supplementary material 6 Conclusions and Outlook 6.1 What is the statistical impact of cyclone passages on sea-ice concentration (SIC) in the Atlantic Arctic Ocean? 6.2 What are the individual contributions of dynamic and thermodynamic processes to sea-ice changes related to cyclones? 6.3 Do the SIC impacts of cyclones change in a warming Arctic and what are the related mechanisms? 6.4 Ways forward Appendix: Cyclones modulate the control of the North Atlantic Oscillation on transports into the Barents Sea Bibliography
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