Modelling and parameterization of lead generated turbulence in the atmospheric boundary layer over Antarctic sea ice

• Applicants: Dr. Micha Gryschka; Dr. Christof Lüpkes; Professor Dr. Detlef Stammer, since 5/2018
• Subject Area: Atmospheric Science
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 314651818

In this project we investigate turbulent atmospheric processes over leads (channels either open or with thin ice cover) in Antarctic sea ice. Especially during winter such inhomogeneities in the sea ice cover generate atmospheric convection with strong turbulent eddies influencing atmospheric boundary layer processes and air ice interaction on the downstream side of leads. Due to the very small scales of these processes they have to be parameterized in state-of-the-art climate models. Although some progress has been achieved in recent years with both high resolution modeling and parameterization many questions need still to be solved to understand the impact of leads on atmospheric boundary layer turbulence in all aspects and to arrive at reliable parameterizations for climate and weather prediction models. These questions concern e.g. the impact of meteorological forcing, of lead geometry, of the sea ice topography, and of small scale organized convection developing over leads. The project is divided into three parts with specific goals. The first goal is to obtain a better understanding of convection processes over leads. To that aim we use state-of-the-art large eddy simulation (LES) for a close-to-reality modeling of atmospheric convection processes over and in the close environment of leads. We consider, for example, the impact of lead geometry and the role of forcing parameters on atmospheric turbulence, and the interaction of the convective plumes over leads with the capping inversion and its impact on vertical entrainment. For the first time a validation of such LES runs is possible on the basis of observed data recently obtained by an aircraft campaign. The second goal is to improve parameterizations of turbulence over leads based on the LES results first for microscale atmospheric non-eddy-resolving models and finally for climate models. Both the modeling (LES and microscale) and parameterization work will be based on previous successful cooperation of the applicants. The new work aims at more complex cases and towards the parameterization in climate models. One of the difficulties for an estimation of the lead impact consists in the difficulties to observe leads from satellite. Thus the modeling and parameterization work will be supported by remote sensing based on high and medium resolution satellite sensors (third goal). With its focus on leads and small scale processes this project contributes to the overarching goal 2.2.4 of the SPP 1158 which intends e.g., to put a strong focus on local impacts particularly important in the polar regions such as the influence of polynyas and leads on the characteristics of the lower atmosphere. We apply for the funding of two PhD students for 3 years, one for the work addressed by goal (1) and one for goal (2). Funding is also necessary for student assistants at University Hamburg (2 years) supporting the remote sensing work addressed in goal (3).

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1158: Antarctic Research with Comparable Investigations in Arctic Sea Ice Areas - with renewal proposal 2025 - 2030
• Ehemaliger Antragsteller: Dr. Lars Kaleschke, until 5/2018