A mechanism for decadal changes of ENSO behavior: roles of background wind changes
A mechanism for decadal changes of ENSO behavior: roles of background wind changes
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DOI：
10.1007/s00382-001-0189-5
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发表时间：
2002-02
期刊：
影响因子：
4.6
通讯作者：
Bin Wang;S. An
中科院分区：
文献类型：
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作者：
Bin Wang;S. An
这项研究解释了为什么自20世纪70年代末以来，厄尔尼诺的一些特性（周期，幅度，结构和传播）以连贯的方式发生了变化，以及为什么这些变化几乎与太平洋十年气候变化同时发生。结果表明，从极移前（1961-1975）到极移后（1981-1995），热带太平洋的表面风场和温度场发生了显著变化，而温跃层的变化则不确定。用Cane和Zebiak模式进行的数值试验表明，地面风场的年代际变化定性地再现了观测到的厄尔尼诺特性的相干变化。改变模式的厄尔尼诺现象的基本因素是背景赤道风和相关的上升流的十年变化。年周期也是平均状态调制厄尔尼诺现象所必需的。从移前到移后时期，背景风和上升流的变化通过重新分配异常大气加热和沿沿着赤道的SST梯度来修改耦合模式的结构（赤道西风异常的东移）。这种结构变化通过增强耦合不稳定性和延迟从暖态到冷态或从冷态到暖态的转变，放大了ENSO循环并延长了振荡周期。平均流和上升流的变化减弱了纬向温度平流的影响，同时增强了垂直平流的影响，因此，盛行的向西传播被东向传播或驻波振荡所取代。我们的研究结果表明，大气桥梁的关键作用，迅速传达的影响，热带地区的年代际变化，太平洋气候变化可能会影响厄尔尼诺现象的性质在20世纪70年代末，通过改变背景的热带风和相关的赤道上升流。
This study explains why a number of El Nino properties (period, amplitude, structure, and propagation) have changed in a coherent manner since the late 1970s and why these changes had almost concurred with the Pacific decadal climate shift. Evidence is presented to show that from the pre-shift (1961–1975) to the post-shift (1981–1995) epoch, significant changes in the tropical Pacific are found in the surface winds and temperature, whereas changes in the thermocline are uncertain. Numerical experiments with the Cane and Zebiak model demonstrate that the decadal changes in the surface winds qualitatively reproduce the observed coherent changes in El Nino properties. The fundamental factor that altered the model's El Nino is the decadal changes of the background equatorial winds and associated upwelling. The annual cycle is also necessary for the mean state to modulate El Nino. From the pre- to post-shift epoch, the changes in the background winds and upwelling modify the structure of the coupled mode (eastward displacement of the equatorial westerly anomalies) by reallocating anomalous atmospheric heating and SST gradient along the equator. This structural change amplifies the ENSO cycle and prolongs the oscillation period by enhancing the coupled instability and delaying transitions from a warm to a cold state or vice versa. The changes in the mean currents and upwelling reduce the effect of the zonal temperature advection while enhance that of the vertical advection; thus, the prevailing westward propagation is replaced by eastward propagation or standing oscillation. Our results suggest a critical role of the atmospheric bridge that rapidly conveys the influences of extratropical decadal variations to the tropics, and the possibility that the Pacific climate shift might have affected El Nino properties in the late 1970s by changing the background tropical winds and the associated equatorial upwelling.