Calvo Natalia, García-Herrera Ricardo, Garcia Rolando R
National Center for Atmospheric Research, Atmospheric Chemistry Division, Boulder, CO 80307-3000, USA.
Ann N Y Acad Sci. 2008 Dec;1146:16-31. doi: 10.1196/annals.1446.008.
Although the El Niño-Southern Oscillation (ENSO) is a tropospheric phenomenon, its effects are also observed in the stratosphere. Traditionally, the study of ENSO above the troposphere has been difficult because of the lack of global observations at high altitudes and also because of the presence of other sources of variability whose signals are difficult to disentangle from ENSO effects. Recent work with general circulation models that isolate the ENSO signal have demonstrated its upward propagation into the stratosphere. Here we review the literature in this field and show results from the most recent version of the Whole Atmosphere Community Climate Model to illustrate the propagation and the mechanisms whereby the signal manifests itself in the stratosphere. The ENSO signal propagates upward to about 40 km by means of large-scale Rossby waves. The propagation is strongly influenced by the zonal mean zonal winds. Most of the strong ENSO events tend to peak in the boreal winter and so the ENSO signal is observed mainly at high latitudes during the Northern Hemisphere winter where the winds are westerly and allow Rossby wave propagation. The ENSO signal is also identified at polar latitudes in the Northern Hemisphere winter in the form of warmer temperatures and weaker winds during a strong El Niño event. This signal shows a zonally homogeneous behavior from the intensification of the stratospheric meridional circulation (in which air rises in the tropics and moves toward the winter pole where it descends) forced by anomalous propagation and dissipation of Rossby waves at middle latitudes during strong ENSO events.
尽管厄尔尼诺-南方涛动（ENSO）是一种对流层现象，但其影响在平流层也能被观测到。传统上，由于缺乏高海拔的全球观测数据，且存在其他变率源，其信号难以与ENSO的影响区分开来，因此对流层以上的ENSO研究一直很困难。最近使用分离ENSO信号的大气环流模型的研究表明，它能向上传播到平流层。在此，我们回顾该领域的文献，并展示最新版本的全大气社区气候模型的结果，以说明信号在平流层中的传播情况及其表现机制。ENSO信号通过大规模罗斯贝波向上传播至约40公里高度。这种传播受到纬向平均纬向风的强烈影响。大多数强ENSO事件往往在北半球冬季达到峰值，因此ENSO信号主要在北半球冬季的高纬度地区被观测到，那里盛行西风，有利于罗斯贝波的传播。在强厄尔尼诺事件期间，ENSO信号在北半球冬季的极地纬度地区也表现为气温升高和风减弱。这种信号在强ENSO事件期间，由于中纬度地区罗斯贝波的异常传播和耗散，强迫平流层经向环流（空气在热带地区上升并向冬季极地方向移动，在那里下沉）加强，从而呈现出纬向均匀的特征。
