The Termination of the 1997-98 El Niño. Part II: Mechanisms of Atmospheric Change
The Termination of the 1997-98 El Niño. Part II: Mechanisms of Atmospheric Change
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DOI：
10.1175/jcli3780.1
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发表时间：
2006-06
影响因子：
4.9
通讯作者：
G. Vecchi
中科院分区：
文献类型：
--
作者：
G. Vecchi
利用全球大气环流模式，探讨了1997-98年厄尔尼诺极端事件结束时，近赤道太平洋纬向风应力(X)变化的驱动机制。分析的重点是1997年10月至1998年5月期间x演变的三个基本特征，它们是驱动这次厄尔尼诺事件结束时海洋变化的基础：(I)1997年11月开始近日期线表面纬向风应力(X)异常的南移，(Ii)1998年2月赤道东太平洋(EEqP)东风x的消失，以及(Iii)1998年5月东风x在EEqP中的再现。结果表明，这些风的变化代表了大气对观测到的海表面温度(SST)场的确定性响应，这是大气对流异常的经向结构随最暖SST经向运动的季节性位相锁定而发生变化的结果。厄尔尼诺事件结束时近日线x异常的南移受控于赤道以南最暖海温的季节性移动，它直接或通过影响大气对海温异常变化的响应，使对流异常从赤道中心向赤道以南中心移动。东风EEqPx的消失(重现)只有在极端厄尔尼诺事件中才明显，并与赤道热带辐合带(ITCZ)的发展(向北撤退)有关。在大气环流模式中，东偏东的EEqP x的消失/回归是对海温场变化的确定性响应，主要与气候海温场的变化(给定的时间不变的极端厄尔尼诺海温场)有关，而不是与底层海温场的变化有关。北半球冬末(北半球晚春)EEqP东风x的消失(回归)是大气对理想化的极端厄尔尼诺海温异常的典型响应，这表明1997-98年厄尔尼诺事件的独特终止是极端厄尔尼诺事件的预期结果。
The mechanisms that drove zonal wind stress ( x ) changes in the near-equatorial Pacific at the end of the extreme 1997–98 El Nino event are explored using a global atmospheric general circulation model. The analysis focuses on three features of the x evolution between October 1997 and May 1998 that were fundamental in driving the oceanic changes at the end of this El Nino event: (i) the southward shift of near-date-line surface zonal wind stress ( x ) anomalies beginning November 1997, (ii) the disappearance of the easterly x from the eastern equatorial Pacific (EEqP) in February 1998, and (iii) the reappearance of easterly x in the EEqP in May 1998. It is shown that these wind changes represent the deterministic response of the atmosphere to the observed sea surface temperature (SST) field, resulting from changes in the meridional structure of atmospheric convective anomalies in response to the seasonally phase-locked meridional movement of the warmest SST. The southward shift of the near-date-line x anomalies at the end of this El Nino event was controlled by the seasonal movement of the warmest SST south of the equator, which—both directly and through its influence on the atmospheric response to changes in SST anomaly—brought the convective anomalies from being centered about the equator to being centered south of the equator. The disappearance (reappearance) of easterly EEqP x has only been evident in extreme El Nino events and has been associated with the development (northward retreat) of an equatorial intertropical convergence zone (ITCZ). The disappearance/return of EEqP easterly x arises in the AGCM as the deterministic response to changes in the SST field, tied principally to the changes in climatological SST (given time-invariant extreme El Nino SSTA) and not to changes in the underlying SSTA field. The disappearance (return) of EEqP easterly x in late boreal winter (late boreal spring) is a characteristic atmospheric response to idealized extreme El Nino SST anomalies; this suggests that the distinctive termination of the 1997–98 El Nino event is that to be expected for extreme El Nino events.