Variability of Sea Level and Upper-Ocean Heat Content in the Indian Ocean: Effects of Subtropical Indian Ocean Dipole and ENSO
Variability of Sea Level and Upper-Ocean Heat Content in the Indian Ocean: Effects of Subtropical Indian Ocean Dipole and ENSO
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DOI：
10.1175/jcli-d-19-0167.1
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发表时间：
2019-09
影响因子：
4.9
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中科院分区：
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本文研究了与副热带印度洋偶极子(SIOD)相关的印度洋上层海洋变率。我们发现，SIOD与南印度洋中西部的一个显著的西南-东北海平面距平(SLA)偶极子有关，北极位于塞舌尔-查戈斯温跃层脊(SCTR)，南极位于马达加斯加东南部，这与海表面温度异常(SSTA)的分布不同。温跃层深度和上层海洋热含量异常反映了SLA，而与SIOD相关的海气CO2通量异常受SSTA控制。在南海地区，热带印度洋东部异常风产生的海洋Rossby波向西传播是导致SLA的主要原因，气旋风在正SIOD(PSIOD)期间引起负SLA。当地风强迫是马达加斯加东南部SLA的主要驱动因素，反气旋风造成正SLA。由于SIOD与ENSO是相关的，因此我们考察了SIOD和ENSO的相对作用。我们发现，虽然ENSO可以通过大气桥梁在南海地区引起显著的SLA，但它对马达加斯加东南部的SLA的影响可以忽略不计。相反，去除了ENSO影响的SIOD与南海和马达加斯加东南部相反的SLA有关，对应于上面确定的SLA偶极子。提出了一种新的副热带偶极子模式指数(SDMI)，它与ENSO不相关，更好地反映了纯SIOD效应。
In this study, the Indian Ocean upper-ocean variability associated with the subtropical Indian Ocean dipole (SIOD) is investigated. We find that the SIOD is associated with a prominent southwest–northeast sea level anomaly (SLA) dipole over the western-central south Indian Ocean, with the north pole located in the Seychelles–Chagos thermocline ridge (SCTR) and the south pole at southeast of Madagascar, which is different from the distribution of the sea surface temperature anomaly (SSTA). While the thermocline depth and upper-ocean heat content anomalies mirror SLAs, the air–sea CO2 flux anomalies associated with SIOD are controlled by SSTA. In the SCTR region, the westward propagation of oceanic Rossby waves generated by anomalous winds over the eastern tropical Indian Ocean is the major cause for the SLAs, with cyclonic wind causing negative SLAs during positive SIOD (pSIOD). Local wind forcing is the primary driver for the SLAs southeast of Madagascar, with anticyclonic winds causing positive SLAs. Since the SIOD is correlated with ENSO, the relative roles of the SIOD and ENSO are examined. We find that while ENSO can induce significant SLAs in the SCTR region through an atmospheric bridge, it has negligible impact on the SLA to the southeast of Madagascar. By contrast, the SIOD with ENSO influence removed is associated with an opposite SLA in the SCTR and southeast of Madagascar, corresponding to the SLA dipole identified above. A new subtropical dipole mode index (SDMI) is proposed, which is uncorrelated with ENSO and thus better represents the pure SIOD effect.