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首页> 外文期刊>Journal of hydrometeorology >Terrain Trapped Airflows and Precipitation Variability during an Atmospheric River Event
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Terrain Trapped Airflows and Precipitation Variability during an Atmospheric River Event

机译：在大气河流活动期间，地形陷阱气流和降水变异

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We examine thermodynamic and kinematic structures of terrain trapped airflows (TTAs) during an atmospheric river (AR) event impacting Northern California 10-11 March 2016 using Alpha Jet Atmospheric eXperiment (AJAX) aircraft data, in situ observations, and Weather and Research Forecasting (WRF) Model simulations. TTAs are identified by locally intensified low-level winds flowing parallel to the coastal ranges and having maxima over the near-coastal waters. Multiple mechanisms can produce TTAs, including terrain blocking and gap flows. The changes in winds can significantly alter the distribution, timing, and intensity of precipitation. We show here how different mechanisms producing TTAs evolve during this event and influence local precipitation variations. Three different periods are identified from the time-varying wind fields. During period 1 (P1), a TTA develops during synoptic-scale onshore flow that backs to southerly flow near the coast. This TTA occurs when the Froude number (Fr) is less than 1, suggesting low-level terrain blocking is the primary mechanism. During period 2 (P2), a Petaluma offshore gap flow develops, with flows turning parallel to the coast offshore and with Fr > 1. Periods P1 and P2 are associated with slightly more coastal than mountain precipitation. In period 3 (P3), the gap flow initiated during P2 merges with a pre-cold-frontal low-level jet (LLJ) and enhanced precipitation shifts to higher mountain regions. Dynamical mixing also becomes more important as the TTA becomes confluent with the approaching LLJ. The different mechanisms producing TTAs and their effects on precipitation pose challenges to observational and modeling systems needed to improve forecasts and early warnings of AR events.
机译：我们在大气河流（AR）事件中影响了地形捕获的气流（TTA）的热力动力学和运动学结构，影响了2016年3月10日至11日的北加州10-11，使用Alpha Jet大气实验（Ajax）飞机数据，原位观察和天气和研究预测（ WRF）模型模拟​​。通过与沿海范围平行的局部强化低水平风识别TTA，并在近岸水域上具有最大值。多种机制可以产生TTA，包括地形阻塞和间隙流。风的变化可以显着改变降水的分布，时序和强度。我们在此显示在此事件期间产生TTA的不同机制如何发展并影响局部降水变化。从时变风场识别出三个不同的时期。在第1期（P1）期间，TTA在概要陆上流动期间开发，以回到海岸附近的南部流动。当Froude号码（FR）小于1时，会发生此TTA，表明低级地形阻塞是主要机制。在第2期（P2）期间，Petaluma海上间隙流动发生，流量与海岸平行于海岸，FR> 1.时段P1和P2与山地降水略微更多的沿海。在第3期（P3）中，在P2期间发起的间隙流与预先冷 - 额落的低级射流（LLJ）合并，并增强了沉淀到更高山地区域的沉淀变化。随着TTA与接近的LLJ变得汇合，动态混合也变得更重要。产生TTA的不同机制及其对降水造成挑战的影响，以改善AR事件的预测和早期警告所需的观察和建模系统。

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