The Critical Role of Non-Normality in Partitioning Tropical and Extratropical Contributions to PNA Growth
The Critical Role of Non-Normality in Partitioning Tropical and Extratropical Contributions to PNA Growth
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DOI：
10.1175/jcli-d-19-0555.1
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发表时间：
2020-07
影响因子：
4.9
通讯作者：
S. A. Henderson;D. Vimont;M. Newman
中科院分区：
文献类型：
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作者：
S. A. Henderson;D. Vimont;M. Newman
太平洋-北美（PNA）遥相关模式既与热带现象有关，包括马登-朱利安振荡（MJO）和厄尔尼诺-南方涛动（ENSO），也与内部温带过程有关，包括与纬向变化的基本状态和天气涡流的相互作用。然而，关于这些不同的关系如何单独或共同作用以产生观察到的 PNA 变异性，仍然存在许多问题。本研究利用线性反演模型 (LIM) 发现，PNA 异常的发展和放大很大程度上是由于与海面温度 (SST) 强耦合的模态（例如 ENSO）和大气内部模态（包括 MJO）的干扰造成的。这些海温耦合和“内部大气”模式形成不正交的子空间，并且 PNA 增长被证明是通过非正态相互作用发生的。开发了内部大气空间 LIM，通过消除海温耦合模式、有效消除 ENSO 并保留 MJO 变异性来检查这种干扰之外的生长。内部大气空间 LIM 中 PNA 的最佳增长是由 MJO 加热（特别是在印度洋上空）和东北太平洋逆行流函数异常驱动的。此外，还研究了热带加热和温带环流对 PNA 生长的单独贡献。非正态 PNA 增长是一个重要结果，表明将 PNA 方差划分为不同现象的贡献是困难的。这一警示性结果可能适用于许多地球物理现象，应在归因研究中予以考虑。
The Pacific–North American (PNA) teleconnection pattern has been linked both to tropical phenomena, including the Madden–Julian oscillation (MJO) and El Niño–Southern Oscillation (ENSO), and to internal extratropical processes, including interactions with the zonally varying basic state and synoptic eddies. Many questions remain, however, concerning how these various relationships act, both separately and together, to yield observed PNA variability. Using linear inverse modeling (LIM), this study finds that the development and amplification of PNA anomalies largely results from the interference of modes strongly coupled to sea surface temperatures (SST), such as ENSO, and modes internal to the atmosphere, including the MJO. These SST-coupled and “internal atmospheric” modes form subspaces that are not orthogonal, and PNA growth is shown to occur via non-normal interactions. An internal atmospheric space LIM is developed to examine growth beyond this interference by removing the SST-coupled modes, effectively removing ENSO and retaining MJO variability. Optimal PNA growth in the internal atmospheric space LIM is driven by MJO heating, particularly over the Indian Ocean, and a retrograding northeast Pacific streamfunction anomaly. Additionally, the individual contributions of tropical heating and the extratropical circulation on PNA growth are investigated. The non-normal PNA growth is an important result, demonstrating the difficulty in partitioning PNA variance into contributions from different phenomena. This cautionary result is likely applicable to many geophysical phenomena and should be considered in attribution studies.