Data from: New perspectives on frontal variability in the southern ocean

The frontal structure of the Southern Ocean is investigated using the Wavelet/Higher Order Statistics Enhancement (WHOSE) frontal detection method, introduced in Chapman (2014). This methodology is applied to 21 years of daily gridded absolute dynamic topography (ADT) data to obtain daily maps of the locations of the fronts. By forming frontal occurrence frequency maps and then approximating these occurrence-maps by a superposition of simple functions, the time-mean locations of the fronts, as well as a measure of their capacity to meander, are obtained and related to the frontal locations found by previous studies. The spatial and temporal variability of the frontal structure is then considered. The number of fronts is found to be highly variable throughout the Southern Ocean, increasing (‘splitting’) downstream of large bathymetric features and decreasing (‘merging’) in regions where the fronts are tightly controlled by the underlying topography. These splitting/merging events are related to changes in the underlying frontal structure whereby regions of high frontal occurrence cross or spread over streamfunction contours. In contrast to the number of fronts, frontal meandering remains relatively constant throughout the Southern Ocean. Little to no migration of the fronts over the 1993-2014 time period is found, and there is only weak sensitivity of frontal positions to atmospheric forcing related to the Southern Annular Mode or the El Niño Southern Oscillation. Finally, the implications of these results for the study of cross-stream tracer transport is discussed.

本研究采用Chapman(2014)提出的小波/高阶统计增强（Wavelet/Higher Order Statistics Enhancement, WHOSE）锋面检测方法，对南大洋锋面结构开展研究。将该方法应用于21年逐日网格化绝对动力地形（absolute dynamic topography, ADT）数据集，以提取锋面位置的逐日分布图。通过构建锋面出现频率图，并利用简单函数的叠加对该频率图进行近似拟合，最终得到锋面的时间平均位置及其蜿蜒能力的量化表征，并将结果与既往研究识别的锋面位置进行对比分析。随后对锋面结构的时空变异特征进行探讨。研究发现，南大洋锋面数量呈现显著的时空变异性：在大型水下地形特征的下游区域，锋面数量会增加（即"分裂"过程）；而在锋面受底层地形严格约束的区域，锋面数量则会减少（即"合并"过程）。此类分裂/合并事件与底层锋面结构的变化存在关联，即高锋面出现频率的区域会跨越或覆盖流函数等值线。与锋面数量不同，南大洋的锋面蜿蜒程度整体保持相对稳定。在1993-2014年的研究时段内，锋面几乎未发生迁移；且锋面位置对与南半球环状模（Southern Annular Mode, SAM）和厄尔尼诺-南方涛动（El Niño Southern Oscillation, ENSO）相关的大气强迫响应微弱，敏感性极低。最后，本文探讨了上述研究结果对跨流示踪剂输运研究的启示意义。