Modulation of westerly wind bursts by sea surface temperature: A semistochastic feedback for ENSO
Modulation of westerly wind bursts by sea surface temperature: A semistochastic feedback for ENSO
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DOI：
10.1175/jas4029.1
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发表时间：
2007-09-01
影响因子：
3.1
通讯作者：
Tziperman, Eli
中科院分区：
文献类型：
--
作者：
Gebbie, Geoffrey;Eisenman, Ian;Tziperman, Eli
赤道太平洋的西风暴发(WWB)在厄尔尼诺事件的发展中起着重要作用。它们通常被视为ENSO的一种纯粹的随机外强迫。然而，最近的观测表明，WWB的特征取决于大尺度的SST场。使用与统计大气模式(即，混合耦合模式)耦合的海洋环流模式，研究了SST对这种WWB调制的后果。在23年观测记录的指导下，一个明确的WWB分量被添加到模型中。WWB参数化方案的构造使得WWB发生的可能性随着西太平洋暖池的扩展而增加：这是一个具有确定性和随机性的“半碎裂”公式。WWB的位置被参数化，以随温水池的边缘迁移。结果表明，海温对WWB的调制对ENSO的特征有很大影响。具体地说，SST和WWB之间的耦合反馈可能足以将系统从阻尼区转移到具有自持续振荡的区。在这个ENSO模式中，调制的WWB也在暖事件的不规则时间和暖事件和冷事件的大小不对称中起到了作用。通过增加线性海气耦合系数来参数化WWB的调制似乎遗漏了重要的动力过程，并且WWBS的纯随机表示只引起了微弱的海洋响应。基于这一证据，提出了WWBS可能需要被视为耦合ENSO系统的一个内部部分，并且可能需要详细的风暴发动力学知识来解释ENSO的特征。
Westerly wind bursts (WWBs) in the equatorial Pacific are known to play a significant role in the development of El Nino events. They have typically been treated as a purely stochastic external forcing of ENSO. Recent observations, however, show that WWB characteristics depend upon the large-scale SST field. The consequences of such a WWB modulation by SST are examined using an ocean general circulation model coupled to a statistical atmosphere model (i.e., a hybrid coupled model). An explicit WWB component is added to the model with guidance from a 23-yr observational record. The WWB parameterization scheme is constructed such that the likelihood of WWB occurrence increases as the western Pacific warm pool extends: a "semistochastic" formulation, which has both deterministic and stochastic elements. The location of the WWBs is parameterized to migrate with the edge of the warm pool. It is found that modulation of WWBs by SST strongly affects the characteristics of ENSO. In particular, coupled feedbacks between SST and WWBs may be sufficient to transfer the system from a damped regime to one with self-sustained oscillations. Modulated WWBs also play a role in the irregular timing of warm episodes and the asymmetry in the size of warm and cold events in this ENSO model. Parameterizing the modulation of WWBs by an increase of the linear air sea coupling coefficient seems to miss important dynamical processes, and a purely stochastic representation of WWBs elicits only a weak ocean response. Based upon this evidence, it is proposed that WWBs may need to be treated as an internal part of the coupled ENSO system, and that the detailed knowledge of wind burst dynamics may be necessary to explain the characteristics of ENSO.