A brief study of the force balance between a small iceberg, the ocean, sea ice, and atmosphere in the Weddell Sea
A brief study of the force balance between a small iceberg, the ocean, sea ice, and atmosphere in the Weddell Sea
复制标题
DOI：
10.1016/j.coldregions.2011.10.014
复制
发表时间：
2012-06-01
影响因子：
4.1
通讯作者：
Goldberg, Dan
中科院分区：
文献类型：
--
作者：
Morison, Jamie;Goldberg, Dan
冰山是威德尔海淡水的重要来源。一套独特的海洋学和其他观测期间的毛德上升非线性状态方程研究围绕一个小冰山，无处不在的冬季威德尔海，让我们有机会研究冰山之间的相互作用的动态和海洋。我们的研究破冰船Nathaniel Palmer使用雷达范围和方位绘制了冰山的地图，发现冰山在水面上宽约200米，吃水深度估计为219米。对于这种尺寸，形状阻力在大气和海洋中都占主导地位。海冰在冰山的上风侧形成脊状，而薄海冰和开阔水域则在下风侧。冰山漂移0.14米秒（-1），或约3%的风速和23度向左。通过船的月池操作的自动CTD用于测量冰山上游、下游和侧面的温度和盐度剖面。这些剖面图显示了冰山上游150米深和下游60米深的混合上层。整个密度跃层的密度差为0.05 kg m（-3），对于平均密度跃层深度为105 m且冰山尺寸对应于等于0.166 m s（-1）的界面内波速度。这和密度跃层深度的上游-下游差异与冰山运动产生的+/- 45 m内波尾流一致。我们估计形状阻力和内部尾流对总水阻力的贡献大致相等。与理论相一致，使用所观察到的密度跃层位移的定性参数表明，内部尾流阻力应该是最大的时候，冰山草案密度跃层深度附近。冰山（和海冰）相对于风速的漂移率接近我们在莫德内斯期间遇到的威德尔海冰的相对漂移率，但比冰山上的大气形状阻力与海洋形状阻力的纯粹平衡大三倍。因此，海冰对冰山的作用力（由迎风侧的脊状突起证明）在海冰漂移速度下移动冰山方面占主导地位。以观测到的速率驱动海冰所需的通过海冰传递的力相当于作用在7.5 km（2）海冰面积上的风应力。在0.5m厚的海冰中，最大起脊力应足以在0.56 m s（-1）的219 m吃水下驱动冰山，这比观测到的漂移率大得多，但与威德尔海风暴期间的海冰速度相似。(C)2011 Elsevier B. V.保留所有权利。
Icebergs are an important source of freshwater to the Weddell Sea. A unique set of oceanographic and other observations made during the Maud Rise Nonlinear Equation of State Study around one of the small icebergs, ubiquitous in the winter Weddell Sea, give us the opportunity to examine the dynamics of the interaction between an iceberg and the ocean. The iceberg was mapped using radar ranges and bearings from our ship, the research icebreaker Nathaniel Palmer, and found to be about 200 m wide above the water with a draft estimated to be 219 m. For this size, form drag dominates skin friction in both the atmosphere and ocean. Sea ice was ridged against the upwind side of the iceberg and thin sea ice and open water were on the downwind side. The iceberg was drifting 0.14 m s(-1), or about 3% of the wind speed and 23 degrees to the left. An automated CTD operating through the ship's moon-pool was used to measure temperature and salinity profiles upstream, downstream, and to the side of the iceberg. These profiles show a mixed upper layer 150 m deep upstream and 60 m deep downstream of the iceberg. The difference in density across the pycnodine was 0.05 kg m(-3), which for the average pycnocline depth of 105 m and size of the iceberg corresponds to an interfacial internal wave speed equal to 0.166 m s(-1). This and the upstream-downstream difference in pycnocline depth are consistent with a +/- 45 m internal wave wake being generated by the motion of the iceberg. We estimate the contributions to total water drag from form drag and generation of the internal wake to be about equal. Consistent with theory, a qualitative argument using the observed pycnocline displacements suggests that internal wake drag should be a maximum when iceberg drafts are near the pycnocline depth. The drift rate of the iceberg (and sea ice) relative to wind speed was near the relative drift rate for the Weddell Sea ice we encountered during MaudNESS, but three times greater than what would result from a pure balance of atmospheric form drag against ocean form drag on the iceberg. Therefore, the force of sea ice on the iceberg, evidenced by ridging on the upwind side was dominant in moving the iceberg with the sea ice drift speed. The force transmitted through the sea ice required to drive the ice at the observed rate would be equivalent to the wind stress acting on an area of sea ice of 7.5 km(2). Maximum ridging forces in the 0.5 m thick sea ice should be adequate to drive the iceberg with this 219-m draft at 0.56 m s(-1), much more than the observed drift rate but similar to the sea ice velocities during Weddell Sea storms. (C) 2011 Elsevier B.V. All rights reserved.