Modelling and parametrization of turbulent convective processes over leads in sea ice

• Main Author: Michaelis, Janosch
• Format: Thesis
• Language: unknown
• Published: 2020
• Subjects: Sea ice
• Online Access: https://epic.awi.de/id/eprint/53652/; https://epic.awi.de/id/eprint/53652/1/Dissertation_JanoschMichaelis.pdf; https://media.suub.uni-bremen.de/handle/elib/4631; https://hdl.handle.net/10013/epic.c1fff940-9545-4485-82c3-3b7309b319c1

In the polar ocean regions, the Earth’s climate system is characterised by many different interaction processes between atmosphere, ocean, and sea ice. Especially between late autumn and spring, the sea ice cover plays a very important role in this system due to its mainly insulating effect, which minimises the exchange of energy between the ocean and the atmosphere. Nonetheless, also in the cold season with large sea ice cover, a strong turbulent transport of heat and moisture is possible between the relatively warm ocean and the cold atmosphere, for example, through elongated open-water channels in sea ice, which are called leads. The convective atmospheric transport over leads is driven mainly by large spatial temperature differences causing plumes with enhanced turbulent transport, which strongly affect the characteristics of the atmospheric boundary layer (ABL) depending on both lead geometry and meteorological forcing. Understanding and quantifying these rather small-scale physical processes is crucial for improving model results also on larger scales and for obtaining accurate projections of the future climate. The focus of this thesis lies on a detailed investigation of the atmospheric processes related to the flow over leads, predominantly by means of small-scale numerical modelling. The applied model uses grid sizes so that the convective plume but not the single turbulent eddies are resolved, which requires turbulence parametrization and validation of the corresponding results. The central part of this thesis is the derivation of an improved parametrization to describe the turbulent fluxes over leads of different width. The new parametrization follows a non-local approach and it is derived based on an already existing closure, but, as a new feature, the lead width is included as a parameter. Small-scale model results obtained with the new parametrization as well as with already existing approaches are evaluated in this thesis for different idealised and observed situations. As a first step, for the ...