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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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  • 2
    Publication Date: 2024-02-21
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉We quantify sea ice concentration (SIC) changes related to synoptic cyclones separately for each month of the year in the Greenland, Barents and Kara Seas for 1979–2018. We find that these SIC changes can be statistically significant throughout the year. However, their strength varies from region to region and month to month, and their sign strongly depends on the considered time scale (before/during vs. after cyclone passages). Our results show that the annual cycle of cyclone impacts on SIC is related to varying cyclone intensity and traversed sea ice conditions. We further show that significant changes in these cyclone impacts have manifested in the last 40 years, with the strongest changes occurring in October and November. For these months, SIC decreases before/during cyclones have more than doubled in magnitude in the Barents and Kara Seas, while SIC increases following cyclones have weakened (intensified) in the Barents Sea (Kara Sea).〈/p〉
    Description: Plain Language Summary: We study how the sea ice cover in the Arctic Ocean changes due to the passage of low‐pressure systems (cyclones). Our study covers all years between 1979 and 2018 and each individual month of the year. Our results show that the passage of cyclones can affect the sea ice year around, but the strength and the sign (less or more sea ice concentration due to cyclones) of this impact varies strongly. These variations in cyclone impacts throughout the year are related to variations in the strength of the cyclones and changes in the state of the sea ice cover (e.g., thinner vs. thicker ice). We further show that the cyclone impact on the Arctic sea ice has changed during the last 40 years. These changes are strongest in autumn, particularly in October and November. In these months, the strength of the destructive cyclone impacts on sea ice has more than doubled in some regions of the Arctic compared to previous times. In some regions, however, also the strength of ice preserving cyclone impacts (more sea ice due to cyclones) has intensified recently.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Cyclones can significantly impact the sea ice in the Atlantic Arctic in all months of the year, but with strong spatiotemporal variations〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Impacts are stronger in the cold season than in summer due to variations in cyclone intensity and traversed sea ice conditions〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Significant changes emerged throughout the year, recently strongest in the Barents Sea in autumn due to a reduced mean ice concentration〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Horizon 2020 Framework Programme http://dx.doi.org/10.13039/100010661
    Description: https://doi.org/10.24381/cds.adbb2d47
    Description: https://www.cen.uni-hamburg.de/icdc/data/ocean/easy-init-ocean/ecmwf-oras5.html
    Keywords: ddc:551.5 ; cyclones ; sea ice ; Arctic ; atmosphere‐sea ice interactions ; climate change
    Language: English
    Type: doc-type:article
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  • 3
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    In:  (Bachelor thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 50 pp
    Publication Date: 2016-10-26
    Keywords: Course of study: BSc Physics of the Earth System
    Type: Thesis , NonPeerReviewed
    Format: text
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  • 4
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    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(17), ISSN: 0094-8276
    Publication Date: 2023-09-08
    Description: We quantify sea ice concentration (SIC) changes related to synoptic cyclones separately for each month of the year in the Greenland, Barents and Kara Seas for 1979–2018. We find that these SIC changes can be statistically significant throughout the year. However, their strength varies from region to region and month to month, and their sign strongly depends on the considered time scale (before/during vs. after cyclone passages). Our results show that the annual cycle of cyclone impacts on SIC is related to varying cyclone intensity and traversed sea ice conditions. We further show that significant changes in these cyclone impacts have manifested in the last 40 years, with the strongest changes occurring in October and November. For these months, SIC decreases before/during cyclones have more than doubled in magnitude in the Barents and Kara Seas, while SIC increases following cyclones have weakened (intensified) in the Barents Sea (Kara Sea).
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
    Publication Date: 2023-04-17
    Description: We utilize a nudged simulation with the coupled regional atmosphere-ocean-sea ice model HIRHAM–NAOSIM over the Arctic to conduct an in-depth analysis of the impact of a sequence of three intense cyclones on the sea ice cover in the Barents and Kara Seas in February 2020. To clarify the underlying mechanisms we decompose changes in sea ice concentration (SIC) and thickness (SIT) into their dynamic and thermodynamic contributions and analyze them in concert with simulated changes in the wind forcing and the surface energy budget. Our findings reveal that changes in SIT during and after the cyclone passages are mostly driven by dynamic processes such as increased ice drift and deformation. With respect to SIC, the relative importance of dynamics and thermodynamics depends on the considered time scale and on the general conditions of the cyclone passages. If cyclones follow on each other in rapid succession, dynamic mechanisms dominate the SIC response for time scales of more than 2 weeks and thermodynamic effects via advection of warm-moist/cold-dry air masses on the cyclone’s front/back side only play a secondary role. However, if sufficiently long time elapses until the arrival of the next storm, thermodynamic SIC increase due to refreezing under the influence of cold and dry air at the backside of the cyclone becomes the dominating mechanism during the days following the cyclone passage.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(22), ISSN: 0094-8276
    Publication Date: 2023-06-21
    Description: Based on the ERA5 reanalysis, we report on statistically significant impacts of transient cyclones on sea ice concentration (SIC) in the Atlantic sector of the Arctic Ocean in winter under “New Arctic” conditions (2000–2020). This includes a pattern of reduced SIC prior to and during cyclones for the whole study domain, while a regional difference between increased SIC in the Barents Sea and reduced SIC in the Greenland Sea is found as the net effect from 3 days prior to 5 days after the cyclone passage. Generally, locally low to medium SIC conditions combined with intense cyclones drive highest SIC changes. There are indications that both thermodynamic and dynamic effects contribute to the SIC changes, but a detailed quantification is required in future research. We provide evidence that cyclone impacts on SIC have amplified compared to the “Old Arctic” (1979–1999), particularly in the Barents Sea.
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    Springer Nature
    In:  EPIC3Communications Earth & Environment, Springer Nature, 4(1), pp. 324-324, ISSN: 2662-4435
    Publication Date: 2024-04-22
    Description: The warm Atlantic Water transported into the Barents Sea plays a crucial role in winter sea ice extent, marine ecosystems, and mid-latitude weather. The North Atlantic Oscillation is known to be an important driver for the Atlantic Water transport variability in the Barents Sea Opening. Here, we find that the dependence of the Barents Sea Opening ocean volume transport variability on the North Atlantic Oscillation is non-stationary. Our results indicate that for the period 1995 to 2005, the link between the North Atlantic Oscillation and the transport variability in the Barents Sea Opening temporarily weakened before an eventual recovery. During this period, synoptic cyclones with unusual trajectories as a consequence of pronounced atmospheric blocking in the North Atlantic sector altered the large-scale and local wind patterns. This temporarily caused a state that the Barents Sea Opening transport variability is largely locally driven instead of being driven by the North Atlantic Oscillation. Our study suggests that an adequate representation of both the North Atlantic Oscillation and cyclone activity is necessary for climate models to better predict future changes in poleward ocean heat transport and Arctic climate.
    Repository Name: EPIC Alfred Wegener Institut
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