Introduction of parameterized sea ice drag coefficients into ice free-drift modeling
-
摘要: 海冰运动的很多特征都依赖于冰与大气的拖曳系数(Ca)以及与海洋的拖曳系数(Cw)。与定义为常数的拖曳系数相比,利用参数化的拖曳系数可以更清楚的认识海冰运动特征随冰情的变化。在本研究中,将拖曳系数参数化引入到海冰的自由漂流模型中,从而探讨风速系数α、偏转角度θ、Ca/Cw等特征参数随局地拖曳系数、浮冰和冰脊几何形态的变化情况。结果显示,在理想的静止海洋中,对于边缘区的小尺寸浮冰,Ca/Cw随冰密集度(A)增大显著增大;而对于中心区的大浮冰,Ca/Cw的变化相对较小(0.2-0.25)。风速系数α随着密集度增加快速增加,但当A>20%后,α趋于稳定值0.018。偏转角度θ随着密集度增加从80°快速减小,当A>20%后,θ的减小趋势变缓,但是并无稳定值。这些参数的变化范围与前人在北极的现场观测结果非常吻合。冰脊强度是确定摩拖曳系数值(Cs'/Cs)与冰脊形拖曳系数值(Cr'/Cr)在Ca/Cw、α和θ中谁占支配地位的重要参数,因为冰脊强度大时,冰脊形拖曳力在总拖曳力中占优;而冰脊强度小时,冰面摩拖曳力在总拖曳力中占优。拖曳系数参数化在将来可以嵌入到其他海冰动力学模型中,从而更好的解释快速变化的北冰洋。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
-
Arya S P S. 1975. A drag partition theory for determining the largescale roughness parameter and wind stress on the Arctic pack ice. Journal of Geophysical Research, 80(24): 3447-3454 Banke E G, Smith S D. 1975. Measurement of form drag on ice ridges. AIDJEX Bulletin, 28: 21-27 Castellani G, Lüpkes C, Hendricks S, et al. 2014. Variability of Arctic sea-ice topography and its impact on the atmospheric surface drag. Journal of Geophysical Research, 119(10): 6743-6762 Davis N R, Wadhams P. 1995. A statistical analysis of arctic pressure ridge morphology. Journal of Geophysical Research, 100(C6): 10915-10925 Edson J B, Fairall C W, Mestayer P G, et al. 1991. A study of the inertial-dissipation method for computing air-sea fluxes. Journal of Geophysical Research, 96(C6): 10689-10711 Fujisaki A, Yamaguchi H, Toyota T, et al. 2009. Measurements of airice drag coefficient over the ice-covered Sea of Okhotsk. Journal of Oceanography, 65(4): 487-498 Hoerner S F. 1965. Fluid-dynamic drag: Practical information on aerodynamic drag and hydrodynamic resistance. Midland Park, N J: Hoerner Fluid Dynamics Leppäranta M. 2011. The Drift of Sea Ice. 2nd ed. Berlin: Springer Leppäranta M, Omstedt A. 1990. Dynamic coupling of sea ice and water for an ice field with free boundaries. Tellus A, 42(4): 482-495 Lu Peng, Li Zhijun, Cheng Bin, et al. 2011. A parameterization of the ice-ocean drag coefficient. Journal of Geophysical Research, 116(C7): C07019 Lu Peng, Li Zhijun. 2014a. On the ratio of atmospheric drag coefficient to oceanic drag coefficient of sea ice. In: Proceedings of the 22nd International Symposium on Ice. Singapore, 703-710 Lu Peng, Li Zhijun. 2014b. Uncertainties in retrieved ice thickness from freeboard measurements due to surface melting. Annals of Glaciology, 55(66): 205-212 Lüpkes C, Birnbaum G. 2005. Surface drag in the Arctic marginal seaice zone: A comparison of different parameterisation concepts. Boundary-Layer Meteorology, 117(2): 179-211 Lüpkes C, Gryanik V M, Hartmann J, et al. 2012. A parametrization, based on sea ice morphology, of the neutral atmospheric drag coefficients for weather prediction and climate models. Journal of Geophysical Research, 117(D13): D13112 Lüpkes C, Gryanik V M, Rösel A, et al. 2013. Effect of sea ice morphology during Arctic summer on atmospheric drag coefficients used in climate models. Geophysical Research Letters, 40(2): 446-451 Martinson D G, Wamser C. 1990. Ice drift and momentum exchange in winter Antarctic pack ice. Journal of Geophysical Research, 95(C2): 1741-1755 McPhee M G. 2002. Turbulent stress at the ice/ocean interface and bottom surface hydraulic roughness during the SHEBA drift. Journal of Geophysical Research, 107(C10): SHE 11-1-SHE 11-15 Olason E, Notz D. 2014. Drivers of variability in Arctic sea-ice drift speed. Journal of Geophysical Research, 119(9): 5755-5775 Pite H D, Topham D R, van Hardenberg B J. 1995. Laboratory measurements of the drag force on a family of two-dimensional ice keel models in a two-layer flow. Journal of Physical Oceanography, 25(12): 3008-3031 Renner A H H, Gerland S, Haas C, et al. 2014. Evidence of Arctic sea ice thinning from direct observations. Geophysical Research Letters, 41(14): 5029-5036 Steiner N. 2001. Introduction of variable drag coefficients into sea-ice models. Annals of Glaciology, 33(1): 181-186 Thorndike A S, Colony R. 1982. Sea ice motion in response to geostrophic winds. Journal of Geophysical Research, 87(C8): 5845-5852 Tsamados M, Feltham D L, Schroeder D, et al. 2014. Impact of variable atmospheric and oceanic form drag on simulations of Arctic sea ice. Journal of Physical Oceanography, 44(5), 1329-1353 Wright B, Hnatiuk J, Kovacs A. 1978. Sea ice pressure ridges in the Beaufort Sea. In: Proceedings of IAHR Ice Symposium. Lulea, Sweden
点击查看大图
计量
- 文章访问数: 1643
- HTML全文浏览量: 96
- PDF下载量: 1107
- 被引次数: 0