Effects of Buoyancy and Wind Forcing on Southern Ocean Climate Change
Effects of Buoyancy and Wind Forcing on Southern Ocean Climate Change
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DOI：
10.1175/jcli-d-19-0877.1
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发表时间：
2020-12
影响因子：
4.9
通讯作者：
Jia‐Rui Shi;L. Talley;S. Xie;Wei Liu;S. Gille
中科院分区：
文献类型：
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作者：
Jia‐Rui Shi;L. Talley;S. Xie;Wei Liu;S. Gille
观测表明，自20世纪50年代以来，南大洋储存了大量人为产生的热量，其表面已经变冷。这些模式可归因于地表强迫的两个组成部分：极地增强的西风和淡水和热量带来的浮力通量增加。在这里，我们通过使用一种新的部分耦合技术来分离这两个强迫分量的影响。我们发现浮力强迫主导了南大洋温度和盐度结构的整体响应。风应力的变化导致地下温度和盐度的变化，这与残余经向翻转环流的增强密切相关。作为一个重要的结果，我们表明浮力和风强迫导致相反的盐度变化：由于更咸的地下水上涌而引起的风诱导的表面盐度增加抵消了由于全球水循环放大而引起的表面清新。浮力和风强迫进一步导致南极环极流（ACC）垂直结构的变化；浮力强迫通过增加在2000 m上部横跨ACC的经向密度梯度导致ACC输运增加（3.1±1.6 Sv; 1 Sv≡106m3s−1），而风致响应更偏向正压性，整个柱输运增加8.7±2.3 Sv。虽然以往的研究主要集中在风对ACC强度的影响上，但我们发现ACC内部的表面水平流加速度主要由浮力强迫主导。这些结果揭示了在全球变暖的影响下，南大洋可能会发生怎样的变化，有助于对未来做出更可靠的预测。
Observations show that since the 1950s, the Southern Ocean has stored a large amount of anthropogenic heat and has freshened at the surface. These patterns can be attributed to two components of surface forcing: poleward-intensified westerly winds and increased buoyancy flux from freshwater and heat. Here we separate the effects of these two forcing components by using a novel partial-coupling technique. We show that buoyancy forcing dominates the overall response in the temperature and salinity structure of the Southern Ocean. Wind stress change results in changes in subsurface temperature and salinity that are closely related to intensified residual meridional overturning circulation. As an important result, we show that buoyancy and wind forcing result in opposing changes in salinity: the wind-induced surface salinity increase due to upwelling of saltier subsurface water offsets surface freshening due to amplification of the global hydrological cycle. Buoyancy and wind forcing further lead to different vertical structures of Antarctic Circumpolar Current (ACC) transport change; buoyancy forcing causes an ACC transport increase (3.1 ± 1.6 Sv; 1 Sv ≡ 106m3s−1) by increasing the meridional density gradient across the ACC in the upper 2000 m, while the wind-induced response is more barotropic, with the whole column transport increased by 8.7 ± 2.3 Sv. While previous research focused on the wind effect on ACC intensity, we show that surface horizontal current acceleration within the ACC is dominated by buoyancy forcing. These results shed light on how the Southern Ocean might change under global warming, contributing to more reliable future projections.