Introduction of parameterized sea ice drag coefficients into ice free-drift modeling
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Introduction of parameterized sea ice drag coefficients into ice free-drift modeling LU Peng1*, LI Zhijun1, HAN Hongwei1 1 Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China
Received 1 November 2014; accepted 18 March 2015 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2016
Abstract
Many interesting characteristics of sea ice drift depend on the atmospheric drag coefficient (Ca) and oceanic drag coefficient (Cw). Parameterizations of drag coefficients rather than constant values provide us a way to look insight into the dependence of these characteristics on sea ice conditions. In the present study, the parameterized ice drag coefficients are included into a free-drift sea ice dynamic model, and the wind factor α and the deflection angle θ between sea ice drift and wind velocity as well as the ratio of Ca to Cw are studied to investigate their dependence on the impact factors such as local drag coefficients, floe and ridge geometry. The results reveal that in an idealized steady ocean, Ca/Cw increases obviously with the increasing ice concentration for small ice floes in the marginal ice zone, while it remains at a steady level (0.2–0.25) for large floes in the central ice zone. The wind factor α increases rapidly at first and approaches a steady level of 0.018 when A is greater than 20%. And the deflection angle θ drops rapidly from an initial value of approximate 80° and decreases slowly as A is greater than 20% without a steady level like α. The values of these parameters agree well with the previously reported observations in Arctic. The ridging intensity is an important parameter to determine the dominant contribution of the ratio of skin friction drag coefficient (Cs’/Cs) and the ratio of ridge form drag coefficient (Cr’/Cr) to the value of Ca/Cw, α, and θ, because of the dominance of ridge form drag for large ridging intensity and skin friction for small ridging intensity among the total drag forces. Parameterization of sea ice drag coefficients has the potential to be embedded into ice dynamic models to better account for the variability of sea ice in the transient Arctic Ocean. Key words: sea ice, drag coefficient, parameterization, free drift, modeling Citation: Lu Peng, Li Zhijun, Han Hongwei. 2016. Introduction of parameterized sea ice drag coefficients into ice free-drift modeling. Acta Oceanologica Sinica, 35(1): 53–59, doi: 10.1007/s13131-016-0796-y
1 Introduction The atmospheric and oceanic drag coefficients of sea ice are the key parameters describing the momentum exchanges at the air-ice and ice-ocean interfaces, determining the drag forces on ice floes exerted by wind and ocean current. A number of empirical values of drag coefficients suitable for specific regions have been derived using the common methods such as the eddy correlation method (Fujisaki et al., 2009), profile method (McPhee, 2002), inertial dissipation method (Edson et al., 1991) and momentum method (Martinson and Wamser, 1990). However, under the ba
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