Mechanism for Southward Shift of Zonal Wind Anomalies During the Mature Phase of ENSO
Mechanism for Southward Shift of Zonal Wind Anomalies During the Mature Phase of ENSO
复制标题
ENSO成熟期纬向风异常南移机制
DOI：
10.1175/jcli-d-21-0078.1
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发表时间：
2021
影响因子：
4.9
通讯作者：
Li, Tim
中科院分区：
文献类型：
--
作者：
Gong, Yuhan;Li, Tim
通过观测分析和数值模式试验，探讨了ENSO成熟冬季赤道中太平洋（CEP）纬向风异常南移的原因。利用ERA-Interim逐日资料诊断了一个反对称的纬向动量收支，提出了一个两步物理机制。第一步是气候平均纬向风对纬向风异常的平流作用。第二步是CEP中反对称模态的发展，它促进了气压梯度和科里奥利力对观测到的纬向风趋势的积极贡献。两个正反馈是负责反对称模式的增长。第一种是水汽-对流-环流反馈，第二种是风-蒸发-SST反馈。大气环流模式试验进一步表明，北半球冬季背景状态是造成纬向风异常南移的关键，当北半球夏季背景状态指定同样的海温异常时，纬向风异常北移。
The cause of the southward shift of anomalous zonal wind in the central equatorial Pacific (CEP) during ENSO mature winter was investigated through observational analyses and numerical model experiments. Based on an antisymmetric zonal momentum budget diagnosis using daily ERA-Interim data, a two-step physical mechanism is proposed. The first step involves advection of the zonal wind anomaly by the climatological mean meridional wind. The second step involves the development of an antisymmetric mode in the CEP, which promotes a positive contribution to the observed zonal wind tendency by the pressure gradient and Coriolis forces. Two positive feedbacks are responsible for the growth of the antisymmetric mode. The first involves the moisture–convection–circulation feedback, and the second involves the wind–evaporation–SST feedback. General circulation model experiments further demonstrated that the boreal winter background state is critical in generating the southward shift, and a northward shift of the zonal wind anomaly is found when the same SST anomaly is specified in boreal summer background state.