An Assessment of Density-Based Finescale Methods for Estimating Diapycnal Diffusivity in the Southern Ocean
An Assessment of Density-Based Finescale Methods for Estimating Diapycnal Diffusivity in the Southern Ocean
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DOI：
10.1175/jtech-d-12-00241.1
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发表时间：
2013-11
影响因子：
2.2
通讯作者：
M. Frants;G. Damerell;S. Gille;K. Heywood;J. MacKinnon;J. Sprintall
中科院分区：
文献类型：
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作者：
M. Frants;G. Damerell;S. Gille;K. Heywood;J. MacKinnon;J. Sprintall
细尺度估计的diapycnal扩散系数k计算CTD和消耗CTD（XCTD）的数据采样在德雷克通道和南大洋东太平洋部门，并从相同的时间和地点的微观结构测量进行比较。微观结构数据显示，垂直扩散系数是三分之一到五分之一的大，在太平洋东南部的平滑深海平原，因为他们在德雷克海峡，在那里的扩散系数被认为是增强theflow的南极绕极流在粗糙的地形。基于垂直应变估计的细尺度方法成功地捕捉到了东南太平洋低混合制度和德雷克海峡高混合制度之间的空间变异性。同一数据集的索普尺度估计未能捕捉德雷克海峡和东太平洋估计之间的差异。XCTD剖面在滤波后具有比CTD剖面更低的垂直分辨率和更高的噪声水平，导致XCTD k估计值平均比CTD估计值高一个数量级。总体而言，微观结构扩散率估计更好地匹配基于应变的估计比基于索普尺度的估计，CTD数据似乎比XCTD数据表现更好。然而，即使是CTD为基础的应变扩散率估计可以从微观结构扩散率相差近一个数量级，这表明基于密度的精细结构的方法估计混合CTD或XCTD数据有真实的限制在低分层制度，如南大洋。
Finescale estimates of diapycnal diffusivity k are computed from CTD and expendable CTD (XCTD) data sampled in Drake Passage and in the eastern Pacific sector of the Southern Ocean and are compared against microstructure measurements from the same times and locations. The microstructure data show vertical diffusivities that are one-third to one-fifth as large over the smooth abyssal plain in the southeastern Pacific as they are inDrake Passage,where diffusivities are thoughttobe enhanced by theflow of the Antarctic Circumpolar Current over rough topography. Finescale methods based on vertical strain estimates are successful at capturing the spatial variability between the low-mixing regime in the southeastern Pacific and the high-mixing regime of Drake Passage. Thorpe-scale estimates for the same dataset fail to capture the differences between Drake Passage and eastern Pacific estimates. XCTD profiles have lower vertical resolution and higher noise levels after filtering than CTD profiles, resulting in XCTD k estimates that are, on average, an order of magnitude higher than CTD estimates. Overall, microstructure diffusivity estimates are better matched by strain-based estimates than by estimates based on Thorpe scales, and CTD data appear to perform better than XCTD data. However, even the CTD-based strain diffusivity estimates can differ from microstructure diffusivities by nearly an order of magnitude, suggesting that density-based fine-structure methods of estimating mixing from CTD or XCTD data have real limitations in low-stratification regimes such as the Southern Ocean.