Linking Atmospheric Rivers and Warm Conveyor Belt Airflows
Linking Atmospheric Rivers and Warm Conveyor Belt Airflows
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DOI：
10.1175/jhm-d-18-0175.1
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发表时间：
2019-06-01
影响因子：
3.8
通讯作者：
Mbengue, C. O.
中科院分区：
文献类型：
--
作者：
Dacre, H. F.;Martinez-Alvarado, O.;Mbengue, C. O.
如果热带气旋在陆地上移动，与温带气旋相关的极端降水可能会导致洪水。然而，湿空气被输送到旋风分离器的动力机制却鲜为人知。在这篇文章中，我们分析了气旋气候学中的气流，以了解气旋如何重新分配储存在大气中的水分。这种分析表明，在气旋的暖区内，气旋的相对气流相对于气旋传播方向是向后的。这种低层气流(称为支流气流)在到达冷锋时减慢，导致水汽通量汇聚，形成一条高水汽含量带。输送气流的一支转向气旋中心，向温暖的传送带底部提供水分，在那里上升并形成降水。另一支转向从气旋中心输出水汽的气旋中心。当气旋移动时，这种输出会产生高水分的灯丝，标志着气旋的轨迹(通常用于识别大气河流)。我们发现，气旋降水和水汽输送都随着输送气流中水汽含量的增加而增加，从而解释了大气河流和与暖输送带上升相关的降水之间的联系。当气旋经过相对于气旋路径的固定区域时计算的大气水汽收支表明，在气旋前环境中持续蒸发的水汽滋润了支流气流。冷锋后面的蒸发作用在气旋通过后湿润了大气，潜在地为随后的气旋发展预调节了环境。
Extreme precipitation associated with extratropical cyclones can lead to flooding if cyclones track over land. However, the dynamical mechanisms by which moist air is transported into cyclones is poorly understood. In this paper we analyze airflows within a climatology of cyclones in order to understand how cyclones redistribute moisture stored in the atmosphere. This analysis shows that within a cyclone's warm sector the cyclone-relative airflow is rearwards relative to the cyclone propagation direction. This low-level airflow (termed the feeder airstream) slows down when it reaches the cold front, resulting in moisture flux convergence and the formation of a band of high moisture content. One branch of the feeder airstream turns toward the cyclone center, supplying moisture to the base of the warm conveyor belt where it ascends and precipitation forms. The other branch turns away from the cyclone center exporting moisture from the cyclone. As the cyclone travels, this export results in a filament of high moisture content marking the track of the cyclone (often used to identify atmospheric rivers). We find that both cyclone precipitation and water vapor transport increase when moisture in the feeder airstream increases, thus explaining the link between atmospheric rivers and the precipitation associated with warm conveyor belt ascent. Atmospheric moisture budgets calculated as cyclones pass over fixed domains relative to the cyclone tracks show that continuous evaporation of moisture in the precyclone environment moistens the feeder airstream. Evaporation behind the cold front acts to moisten the atmosphere in the wake of the cyclone passage, potentially preconditioning the environment for subsequent cyclone development.