Vacillation cycles and blocking in a channel
Vacillation cycles and blocking in a channel
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DOI：
10.1002/qj.49712454711
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发表时间：
1998-04
影响因子：
8.9
通讯作者：
K. Haines;A. J. Holland
中科院分区：
文献类型：
--
作者：
K. Haines;A. J. Holland
本文研究了两层、β平面准地转航道模式对低频高频造波强迫的响应。造波器模拟规则的斜压不稳定，然后传播到高层大气激发阻塞。通过改变上层的横向剪切，大尺度响应可以从稳定的大幅分裂射流（非常类似于观察到的块体）变化到具有低频摆动周期的较弱分裂。涡总是共振地激发分裂流，但在振荡的情况下，混合不稳定过程是导致分裂的原因，这可以通过简化的纬向稳定性分析和能量趋势诊断来证明。漩涡的再次激发继续循环这个模型提供了一个理论，说明上层风的纬向结构如何决定一个大振幅块体是否可以被激发或在存在从下面向上传播的类似高频涡动活动的情况下持续存在。
The response to a low‐level high‐frequency wavemaker forcing in a two‐layer, β‐plane, quasi‐geostrophic channel model is examined. The wavemaker simulates regular baroclinic instability which then propagates to upper atmospheric levels to excite blocking. By altering the meridional shear in the upper layer, the large‐scale response can vary from a steady large‐amplitude split jet, very similar to observed blocks, to a weaker split with a low‐frequency vacillation cycle. The eddies will always resonantly excite the split flow, but a mixed instability process is responsible for the breakdown in cases which oscillate, and this is demonstrated using a simplified zonal stability analysis and energy‐tendency diagnostics. The re‐excitement by the eddies continues the cycle. This model provides a theory of how the meridional structure of the upper‐level winds may determine whether a large‐amplitude block can be excited or persist in the presence of similar high‐frequency eddy activity propagating up from below.