Southern Hemisphere extra-tropical forcing: a new paradigm for El Niño-Southern Oscillation
Southern Hemisphere extra-tropical forcing: a new paradigm for El Niño-Southern Oscillation
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DOI：
10.1007/s00382-010-0825-z
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发表时间：
2011-06
期刊：
影响因子：
4.6
通讯作者：
P. Terray
中科院分区：
文献类型：
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作者：
P. Terray
本文的主要目的是进一步阐明南半球中纬度气候与El Niño-Southern涛动（ENSO）信号之间的相互动力联系。虽然我们的分析证实ENSO是南半球年际变化的主要来源，但这里也表明，南半球中纬度变化引发的南印度洋和大西洋的副热带偶极子变率也可能对赤道太平洋的ENSO产生控制性影响。这种副热带强迫通过各种耦合的海气反馈作用起作用，包括从北方冬季到北方春季将副热带海温异常传播到大西洋和印度洋的热带深处，以及随后在北方春季开始时对这些连接三个热带盆地的海温异常的大气动力响应。这种大气响应的特征是赤道大西洋和印度热带辐合带（ITCZ）的显著减弱。这种减弱的ITCZ迫使赤道对流层中高层产生“冷开尔文波”响应，从热汇区向东延伸到西太平洋。通过调节赤道西太平洋上空的垂直温度梯度和大气稳定性，这种开尔文波响应促进了赤道西太平洋上空持续的纬向风和对流异常，这可能触发厄尔尼诺Niño在北方冬季结束时的爆发。这些不同的过程解释了为什么南大西洋和印度亚热带偶极子时间序列指数在赤道太平洋El Niño爆发前几个月就成为Niño34海温指数的重要先兆。本研究表明，南半球中纬度地区大气内部变率可能显著影响ENSO变率。然而，这种令人惊讶的关系仅在最近几十年观察到，即所谓的1976/1977年气候变化之后，这表明可能与全球变暖或气候系统的年代际波动有关。
The main goal of this paper is to shed additional light on the reciprocal dynamical linkages between mid-latitude Southern Hemisphere climate and the El Niño-Southern Oscillation (ENSO) signal. While our analysis confirms that ENSO is a dominant source of interannual variability in the Southern Hemisphere, it is also suggested here that subtropical dipole variability in both the Southern Indian and Atlantic Oceans triggered by Southern Hemisphere mid-latitude variability may also provide a controlling influence on ENSO in the equatorial Pacific. This subtropical forcing operates through various coupled air–sea feedbacks involving the propagation of subtropical sea surface temperature (SST) anomalies into the deep tropics of the Atlantic and Indian Oceans from boreal winter to boreal spring and a subsequent dynamical atmospheric response to these SST anomalies linking the three tropical basins at the beginning of the boreal spring. This atmospheric response is characterized by a significant weakening of the equatorial Atlantic and Indian Inter-Tropical Convergence Zone (ITCZ). This weakened ITCZ forces an equatorial “cold Kelvin wave” response in the middle to upper troposphere that extends eastward from the heat sink regions into the western Pacific. By modulating the vertical temperature gradient and the stability of the atmosphere over the equatorial western Pacific Ocean, this Kelvin wave response promotes persistent zonal wind and convective anomalies over the western equatorial Pacific, which may trigger El Niño onset at the end of the boreal winter. These different processes explain why South Atlantic and Indian subtropical dipole time series indices are highly significant precursors of the Niño34 SST index several months in advance before the El Niño onset in the equatorial Pacific. This study illustrates that the atmospheric internal variability in the mid-latitudes of the Southern Hemisphere may significantly influence ENSO variability. However, this surprising relationship is observed only during recent decades, after the so-called 1976/1977 climate regime shift, suggesting a possible linkage with global warming or decadal fluctuations of the climate system.