Midwinter Suppression of Storm Tracks in an Idealized Zonally Symmetric Setting
Midwinter Suppression of Storm Tracks in an Idealized Zonally Symmetric Setting
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DOI：
10.1175/jas-d-18-0353.1
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发表时间：
2019-12
影响因子：
3.1
通讯作者：
Lenka Novak;T. Schneider;Farid Ait-Chaalal
中科院分区：
文献类型：
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作者：
Lenka Novak;T. Schneider;Farid Ait-Chaalal
在北太平洋风暴轴的涡动活动的仲冬抑制是一种现象，抵制复制的理想化模式，初始化独立于所观察到的大气。试图解释它往往集中在当地的机制，依赖于纬向不对称性，如地形对平均流量和涡旋的影响。在这里，一个理想化的水行星GCM被用来证明，仲冬抑制也可以发生在统计纬向对称风暴轴的活动。对于一个仲冬抑制发生，这是必要的，参数，如上层海洋的热惯性和热带海洋能量输送的强度，选择适当的副热带急流特征产生一个明显的季节性周期。如果副热带急流足够强，并且在隆冬期间位于中纬度风暴轴附近，它将主导上层气流，并引导涡旋向赤道方向移动，远离涡旋生成的低层区域。这抑制了风暴轴内上下层之间的斜压相互作用，减弱了涡动活动。然而，在理想化的GCM中，由于副热带急流在冬末继续向极地移动（与观察到的不同），涡动活动再次回升，表明引起仲冬抑制的副热带急流的性质是微妙的。理想化的GCM模拟提供了一个框架，在此框架内，可能的机制引起的隆冬抑制风暴轴可以系统地研究。
The midwinter suppression of eddy activity in the North Pacific storm track is a phenomenon that has resisted reproduction in idealized models that are initialized independently of the observed atmosphere. Attempts at explaining it have often focused on local mechanisms that depend on zonal asymmetries, such as effects of topography on the mean flow and eddies. Here an idealized aquaplanet GCM is used to demonstrate that a midwinter suppression can also occur in the activity of a statistically zonally symmetric storm track. For a midwinter suppression to occur, it is necessary that parameters, such as the thermal inertia of the upper ocean and the strength of tropical ocean energy transport, are chosen suitably to produce a pronounced seasonal cycle of the subtropical jet characteristics. If the subtropical jet is sufficiently strong and located close to the midlatitude storm track during midwinter, it dominates the upper-level flow and guides eddies equatorward, away from the low-level area of eddy generation. This inhibits the baroclinic interaction between upper and lower levels within the storm track and weakens eddy activity. However, as the subtropical jet continues to move poleward during late winter in the idealized GCM (and unlike what is observed), eddy activity picks up again, showing that the properties of the subtropical jet that give rise to the midwinter suppression are subtle. The idealized GCM simulations provide a framework within which possible mechanisms giving rise to a midwinter suppression of storm tracks can be investigated systematically.