Transition from a cold to a warm state of the El Niño-Southern Oscillation cycle
Transition from a cold to a warm state of the El Niño-Southern Oscillation cycle
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DOI：
10.1007/bf01022519
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发表时间：
1995-03
影响因子：
2
通讯作者：
Bin Wang
中科院分区：
文献类型：
--
作者：
Bin Wang
利用1950- 1992年的COADS资料，研究了厄尔尼诺-南方涛动（ENSO）循环由冷到暖的转变过程。厄尔尼诺爆发（前一年的11 - 12月）的特征是在南方涛动“节点”线附近的副热带地区出现最低海平面气压异常。这种气压下降有利于西太平洋异常气旋性环流的形成，并导致厄尔尼诺年春季赤道西太平洋异常西风带的建立。然后，西风异常在厄尔尼诺年结束时加强并传播到太平洋中部。这是海盆变暖发展的一个基本特征，认为西太平洋赤道西风异常的发展可能是海气热力耦合的结果。在北半球的冬季和春季，赤道西太平洋的平均纬向风由西风转为西风。一个温和的赤道西风异常最初施加在这样一个平均状态可能会通过改变蒸发冷却和湍流混合的速率产生向东的SST梯度。赤道SST梯度又会引起差异加热和纬向气压梯度，加强西风异常。东向SST梯度与西风异常之间的反馈作用促进了西风异常的东向传播。
The transition from a cold to a warm state of the E1 Niño-Southern Oscillation (ENSO) cycle is studied using Comprehensive Ocean-Atmosphere Data Sets (COADS) for the period 1950–1992.The onset of El Niño (November to December of the year preceding the El Niño) is characterized by an occurrence of minimum sea-level pressure anomalies in the subtropics around the “node” line of the Southern Oscillation. This pressure fall favors the formation of the anomalous cyclonic circulations over the western Pacific and leads to the establishment of anomalous westerlies in the western equatorial Pacific during the boreal spring of the El Niño year. The westerly anomalies then intensify and propagate into the central Pacific by the end of the El Niño year. This is an essential feature of the development of a basin-wide warming.It is argued that the development of the equatorial westerly anomalies over the western Pacific may result from the thermodynamic coupling between the atmosphere and ocean. In boreal winter and spring the mean zonal winds change from westerly to casterly over the western equatorial Pacific. A moderate equatorial westerly anomaly initially imposed on such a mean state may create eastward SST gradients via changing rates of evaporational cooling and turbulent mixing. The equatorial SST gradients would, in turn, induce differential heating and zonal pressure gradients which reinforce the westerly anomalies. The feedback between the eastward SST gradients and westerly anomalies promotes the eastward propagation of the westerly anomalies.