Parametrization of Turbulent Fluxes over Leads in Sea Ice in a Non-Eddy-Resolving Small-Scale Atmosphere Model

• Main Authors: Michaelis, Janosch, Lüpkes, Christof, Zhou, Xu, Gryschka, Micha, Gryanik, Vladimir M.
• Format: Conference Object
• Language: unknown
• Published: 2019
• Subjects: Sea ice
• Online Access: https://epic.awi.de/id/eprint/50795/; https://epic.awi.de/id/eprint/50795/1/20191209_Poster_AGU_Final.pdf; https://hdl.handle.net/10013/epic.bbb8ac81-7380-4779-bc4d-903e63b8780f

Leads (open-water channels in sea ice) play an important role for surface-atmosphere interactions in the polar regions. Due to large temperature differences between the surface of leads and the near-surface atmosphere, strong turbulent convective plumes are generated with a large impact on the atmospheric boundary layer (ABL). Here, we focus on the effect of lead width on those processes, by means of numerical modeling and turbulence parametrization. We use a microscale atmosphere model in a 2D version resolving the entire convective plume with grid sizes in the range of L/5 where L is the lead width. For the sub-grid scale turbulence, we developed a modified version of an already existing nonlocal parametrization of the lead-generated sensible heat flux including L as parameter. All our simulations represent measured springtime conditions with a neutrally stratified ABL capped by a strong temperature inversion at 300 m height, where the initial temperature difference between the lead surface and the near-surface atmosphere amounts to 20 K. We found that our simulation results obtained with the new approach agree very well with time-averaged results of a large eddy simulation (LES) model for variable lead widths with L ≥ 1 km and different upstream wind speeds. This is a considerable improvement since results obtained with the previous nonlocal approach clearly disagree with the LES results for leads wider than 2 km. In conclusion, considering L as parameter in a nonlocal turbulence parametrization seems to be necessary to study the effect of leads on the polar ABL in non-eddy-resolving small-scale atmosphere models.