Near-Surface Wind Convergence over the Gulf Stream—The Role of SST Revisited
Near-Surface Wind Convergence over the Gulf Stream—The Role of SST Revisited
复制标题
墨西哥湾流近地表风辐合——重新审视海温的作用
DOI：
10.1175/jcli-d-22-0441.1
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发表时间：
2023
影响因子：
4.9
通讯作者：
Chang, P.
中科院分区：
文献类型：
--
作者：
Small, R. J.;Rousseau, V.;Parfitt, R.;Laurindo, L.;O’Neill, L.;Masunaga, R.;Schneider, N.;Chang, P.
高分辨率观测表明，存在强的时间平均近地面风辐合(NSWC)，这种辐合存在于海洋锋区，例如西部边界流。初步分析似乎表明，这一时间平均NSWC与下伏海表面温度的时间平均性质密切相关，例如通过气压调整和垂直混合机制起作用的梯度和二阶导数(例如，SST的拉普拉斯导数)。然而，最近的一系列论文揭示了由大气锋面主导的瞬时NSWC，并提出了在较短的天气时间尺度上发生的海-气过程的重要性。本文利用墨西哥湾流区ERA5再分析资料，旨在通过研究NSWC的时空相关性及其与海温的关系来调和上述观点。结果表明，虽然大气锋面过程控制着NSWC的逐日变化，但相对较弱但持续的气压调整和垂直混合机制在有或没有大气锋面的条件下都提供了较低的频率调制。除了它们的时间特征外，每种机制都通过频谱分析显示在特定的空间尺度上占主导地位。鉴于最近的工作将西部边界洋流区域的远程大气响应与NSWC异常联系在一起，这些结果强调了海洋锋区对大气在所有时空尺度上的变异性的重要性。
High-resolution observations have demonstrated the presence of strong time-mean near-surface wind convergence (NSWC) anchored across oceanic frontal zones, such as the western boundary currents. Initial analyses appeared to show a close association between this time-mean NSWC and time-mean properties of the underlying sea surface temperature (SST), such as the gradients and second derivatives (e.g., Laplacian of SST), acting through pressure-adjustment and vertical-mixing mechanisms. However, a series of recent papers have revealed the instantaneous NSWC to be dominated by atmospheric fronts and have suggested the importance of air–sea processes occurring instead on shorter, synoptic time scales. In this paper, using the ERA5 reanalysis dataset in the Gulf Stream region, we aim to reconcile these viewpoints by investigating the spatial and temporal dependence of NSWC and its relationship to SST. It is revealed that while atmospheric frontal processes govern the day-to-day variability of NSWC, the relatively weak but persistent pressure-adjustment and vertical-mixing mechanisms provide lower-frequency modulations in conditions both with and without atmospheric fronts. In addition to their temporal characteristics, each mechanism is shown through spectral analysis to dominate on specific spatial scales. In light of recent work that has tied remote atmospheric responses to NSWC anomalies in western boundary current regions, these results emphasize the importance of oceanic frontal zones for atmospheric variability on all spatiotemporal scales.