What Distinguishes MJO Events Associated with Atmospheric Rivers?
What Distinguishes MJO Events Associated with Atmospheric Rivers?
复制标题
与大气河相关的 MJO 事件有什么区别？
DOI：
10.1175/jcli-d-21-0493.1
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发表时间：
2022
影响因子：
4.9
通讯作者：
Hakim Gregory J.
中科院分区：
文献类型：
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作者：
Toride Kinya;Hakim Gregory J.
大气河流（AR）是一条狭长的强水汽输送带，经常引起北美西海岸沿着的强降水和洪水。以往的研究表明，Madden-Julian振荡（MJO）有助于在亚季节时间尺度上的AR活动的可预测性。然而，个体AR反应在MJO的相同阶段后变化很大。在这里，我们调查96 MJO事件后第3阶段（印度洋对流），并分析事件之间的差异，带来了大规模的AR的整个太平洋西北沿海地区和那些没有。有AR的MJO事件往往比没有AR的MJO事件在第3阶段停留的时间更长。我们使用线性回归来分离与MJO线性相关的外磁信号，并探索两组之间的剩余场如何不同。线性相关的信号显示了缓慢移动的行星尺度的水汽输送穿过北太平洋。剩余场在阿拉斯加湾表现出与太平洋-北美（PNA）模式类似的对比强烈的低频（>10天）模式：有AR的事件为波谷，没有AR的事件为脊线。这种低频变率改变了太平洋波导，使得对于具有AR的MJO事件，斜压波以有利于异常正IVT的方向定向到太平洋西北部。对于没有AR的MJO事件，脊加强了北太平洋的大规模反气旋流，并阻止水汽进入太平洋西北部。
Atmospheric rivers (ARs) are long and narrow bands of intense water vapor transport that often induce heavy precipitation and flooding along the west coast of North America. Previous studies demonstrate that the Madden–Julian oscillation (MJO) contributes to the predictability of AR activity on a subseasonal time scale. However, individual AR responses vary widely following the same phase of MJO. Here we investigate 96 MJO events following phase 3 (convection over the Indian Ocean) and analyze the differences between events that brought large-scale ARs to the entire Pacific Northwest coastal region and those that did not. The MJO events with ARs tend to stay longer at phase 3 than those without ARs. We use linear regression to isolate the extratropical signals linearly related to the MJO and explore how the residual fields differ between the two groups. The linearly dependent signal shows slow-moving planetary-scale water vapor transport across the North Pacific. The residual field exhibits a contrasting extratropical low-frequency (>10 days) pattern in the Gulf of Alaska resembling the Pacific–North American (PNA) pattern: a trough for events with ARs and a ridge for events without ARs. This low-frequency variability alters the Pacific waveguide such that, for MJO events with ARs, baroclinic waves are directed into the Pacific Northwest with an orientation that favors anomalous positive IVT. For MJO events without ARs, the ridge strengthens large-scale anticyclonic flow over the North Pacific and prevents moisture access to the Pacific Northwest.