TY - JOUR

T1 - Influence of Lead width on the Turbulent Flow Over Sea Ice Leads

T2 - Modeling and Parametrization

AU - Michaelis, Janosch

AU - Lüpkes, Christof

AU - Zhou, Xu

AU - Gryschka, Micha

AU - Gryanik, Vladimir M.

N1 - Funding Information: We thank Tim Gollnik for providing subroutines in METRAS for the flux calculation and for further support to run the model at the German Climate Computing Center (DKRZ). The PALM simulations were performed with resources provided by the North-German Supercomputing Alliance (HLRN). Processing of all data and their visualization were done with MatLab 2019a and 2019b. The study was supported by DFG (grant LU 818/5-1 and GR 4911/1-1). We gratefully acknowledge also the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) Project number 268020496 TRR 172 within the Transregional Collaborative Research Center ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3. We also thank two anonymous reviewers for constructive criticism, which helped to improve the quality of this manuscript. Also comments of Cedrick Ansorge were helpful for improvements.

PY - 2020/8/7

Y1 - 2020/8/7

N2 - A new turbulence parametrization is developed for a non-eddy-resolving microscale model to study the effects of leads (elongated open-water channels in sea ice) of different width on the polar atmospheric boundary layer (ABL). Lead-dominated sea ice regions are characterized by large horizontal inhomogeneities of the surface temperature causing strong convection. Therefore, the new parametrization is based on a previous formulation where inhomogeneous conditions of dry convection over leads and nonlocal effects on heat fluxes had already been taken into account for a fixed lead width. A nonlocal lead width dependent approach is applied now for both heat fluxes and momentum fluxes in the convective region. Microscale model results obtained with the new, the previous nonlocal, and a local parametrization are shown, where 10 idealized cases of a lead-perpendicular, near-neutral ABL-flow below a strong capping inversion are considered. Furthermore, time-averaged large eddy simulation (LES) results of those cases are considered for analyzing the integrated effects of the dry convection on ABL characteristics. Microscale model results obtained with the new nonlocal parametrization agree well with the LES for variable lead widths and different atmospheric forcing although there is a room for further improvement. Furthermore, several features obtained with a local closure clearly disagree with LES. Thus, the microscale study also points to difficulties that might occur in mesoscale studies over regions where leads dominate the flow regime when local closures are applied.

AB - A new turbulence parametrization is developed for a non-eddy-resolving microscale model to study the effects of leads (elongated open-water channels in sea ice) of different width on the polar atmospheric boundary layer (ABL). Lead-dominated sea ice regions are characterized by large horizontal inhomogeneities of the surface temperature causing strong convection. Therefore, the new parametrization is based on a previous formulation where inhomogeneous conditions of dry convection over leads and nonlocal effects on heat fluxes had already been taken into account for a fixed lead width. A nonlocal lead width dependent approach is applied now for both heat fluxes and momentum fluxes in the convective region. Microscale model results obtained with the new, the previous nonlocal, and a local parametrization are shown, where 10 idealized cases of a lead-perpendicular, near-neutral ABL-flow below a strong capping inversion are considered. Furthermore, time-averaged large eddy simulation (LES) results of those cases are considered for analyzing the integrated effects of the dry convection on ABL characteristics. Microscale model results obtained with the new nonlocal parametrization agree well with the LES for variable lead widths and different atmospheric forcing although there is a room for further improvement. Furthermore, several features obtained with a local closure clearly disagree with LES. Thus, the microscale study also points to difficulties that might occur in mesoscale studies over regions where leads dominate the flow regime when local closures are applied.

KW - atmospheric boundary layer

KW - atmospheric turbulence

KW - large eddy simulation

KW - microscale modeling

KW - sea ice leads

KW - turbulence parametrization

UR - http://www.scopus.com/inward/record.url?scp=85089504587&partnerID=8YFLogxK

U2 - 10.15488/16433

DO - 10.15488/16433

M3 - Article

AN - SCOPUS:85089504587

VL - 125

JO - Journal of Geophysical Research: Atmospheres

JF - Journal of Geophysical Research: Atmospheres

SN - 2169-897X

IS - 15

M1 - e2019JD031996

ER -