Buoyancy Forcing Dominates the Cross-Equatorial Ocean Heat Transport Response to Northern Hemisphere Extratropical Cooling
Buoyancy Forcing Dominates the Cross-Equatorial Ocean Heat Transport Response to Northern Hemisphere Extratropical Cooling
复制标题
浮力强迫主导跨赤道海洋热传输对北半球温带变冷的响应
DOI：
10.1175/jcli-d-21-0950.1
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发表时间：
2022
影响因子：
4.9
通讯作者：
Eisenman, Ian
中科院分区：
文献类型：
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作者：
Luongo, Matthew T.;Xie, Shang-Ping;Eisenman, Ian
跨赤道海洋热输送（OHT）的变化已经被发现阻尼热带辐合带（ITCZ）的纬向移动引起的半球不对称的辐射强迫。纬向平均能量输送理论和理想模式模拟表明，这些OHT的变化主要是由于风驱动的变化，在印度太平洋的浅副热带细胞（STC）和浮力驱动的变化，在深大西洋纬向翻转环流（AMOC）。在这项研究中，我们探讨了海洋的响应浮力和动量强迫之间的分区。我们调整大气层顶部的太阳强迫冷却北方半球（NH）外热带地区的一套新的综合气候模式模拟，旨在隔离浮力强迫和动量强迫的变化。在这种情况下，北半球高纬度强迫，我们确认，浮力驱动的变化在AMOC占主导地位的大西洋。然而，与先前的预期相反，浮力驱动的STC变化是印度-太平洋热传输变化的主要驱动力。我们发现，浮力迫使印度-太平洋STC的变化运输近4倍的热量在赤道附近的浅风驱动STC的变化。这种浮力强迫STC响应产生于对流层外密度扰动，这些扰动被低云反馈放大，并通过通风温跃层与热带连通。虽然海洋的具体响应取决于强迫方案，但我们的研究结果表明，将海洋对能量扰动的总响应划分为浮力和动量强迫提供了特定于流域的见解，以了解海洋如何抑制ITCZ迁移的关键方面，而以前的区域平均框架忽略了这些方面。
Cross-equatorial ocean heat transport (OHT) changes have been found to damp meridional shifts of the intertropical convergence zone (ITCZ) induced by hemispheric asymmetries in radiative forcing. Zonal-mean energy transport theories and idealized model simulations have suggested that these OHT changes occur primarily due to wind-driven changes in the Indo-Pacific’s shallow subtropical cells (STCs) and buoyancy-driven changes in the deep Atlantic meridional overturning circulation (AMOC). In this study we explore the partitioning between buoyancy and momentum forcing in the ocean’s response. We adjust the top-of-atmosphere solar forcing to cool the Northern Hemisphere (NH) extratropics in a novel set of comprehensive climate model simulations designed to isolate buoyancy-forced and momentum-forced changes. In this case of NH high-latitude forcing, we confirm that buoyancy-driven changes in the AMOC dominate in the Atlantic. However, in contrast with prior expectations, buoyancy-driven changes in the STCs are the primary driver of the heat transport changes in the Indo-Pacific. We find that buoyancy-forced Indo-Pacific STC changes transport nearly 4 times the amount of heat across the equator as the shallower wind-driven STC changes. This buoyancy-forced STC response arises from extratropical density perturbations that are amplified by the low cloud feedback and communicated to the tropics by the ventilated thermocline. While the ocean’s specific response is dependent on the forcing scheme, our results suggest that partitioning the ocean’s total response to energy perturbations into buoyancy and momentum forcing provides basin-specific insight into key aspects of how the ocean damps ITCZ migrations that previous zonal-mean frameworks omit.