The Multi-Scale Dynamics of Sundowner Wind Systems

Sundowner 风力系统的多尺度动力学

• 批准号: 1419267
• 负责人: Michael Kaplan
• 金额: $ 60.03万
• 依托单位: Nevada System of Higher Education, Desert Research Institute
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1419267&HistoricalAwards=false
• 关键词: Multi; Scale; Dynamics; Sundowner; Wind; Multi; Scale; Dynamics; Sundowner; Wind

The research project seeks to gain a better understanding of the mechanisms that cause Sundowner wind events in Southern California. Sundowner winds are typically associated with extreme heating in the absence of very strong surface wind velocities. Sundowner winds cause conditions favorable for devastating Southern California wildfires making forecasting them critically important and extraordinarily difficult due to their fast and very fine scale onset. The basic hypothesis to be tested spans a multiplicity of scales of motion: At larger scales (meso-alpha/beta) Sundowner wind events are associated with: 1) a low-level coastal jet driven by an upstream coastal pressure gradient accompanying a strong low-level inversion as well as 2) a shallow critical layer and shallow Scorer Parameter discontinuity along the coastal mountains (e.g., Santa Ynez). This low-level coastal jet results from: 1) an inland extension of the thermal gradient between a cold near shore marine boundary layer and an elevated inland, heated convective boundary layer and 2) a reinforcement of coastal high surface pressure (to the NNW of this thermal gradient) by the right exit region of an upstream polar jet streak. At the smaller scales (meso-gamma), wave development involving an internal gravity wave (IGW) breaking develops along the westward-facing slopes of the coastal (Santa Ynez) Mountains, triggering a short-lived rotor above the marine layer. The rotor amplifies and breaks, mixing warmer and drier air rapidly into the marine layer. This mixing represents the first component of rapid Sundowner warming as the cold marine layer is dissipated and replaced by relatively warm air from the residual continental boundary layer. The second component occurs quickly thereafter as the trailing warm pool accompanying the IGW descends the coastal mountains forming a meso-gamma scale wake low resulting in 10-25C° total warming.The methods employed in this research activity primarily involve numerical modeling, observational data analyses and theoretical analyses of several real and idealized data case studies. The Weather Research and Forecasting (WRF) model will be employed to simulate numerous Sundowner wind case studies ranging from extreme to marginal to null case studies. The events will be classified based on observed surface wind gust and heating intensities and the numerical modeling will involve a complete spectrum of cases. The horizontal grids will range in resolution from ~10 km regionally to ~666 m in the specific locations of Sundowner wind genesis depending on terrain gradient shape and magnitude thus allowing the scale contraction of simulated fields.The intellectual merit of this research activity is to understand the multi-scale mechanisms causing Sundowner wind events and their sensitivity to synoptic and multiple mesoscale dynamics involving both the marine layer and very fine scale terrain structure. In particular, more detailed understanding will be derived of how larger scale jet adjustments establish the mesoscale wind and temperature gradients that can be perturbed by terrain to generate meso-gamma scale mountain waves, bores and wake lows. Furthermore, how the marine layer, mountain wave, and larger scale jets interact in the Sundowner wind that occurs in the fire-prone regions near Santa Barbara, California.The broader impacts of this research activity will involve weather forecasting advancements in this region, most notably predicting conditions that result in extreme wildfire danger. The inability of operational computer models to simulate the finer scale characteristics of Sundowner winds makes it much more difficult for the National Weather Service (NWS), private forecasters and local emergency responders to warn/prepare for fire events. The public is extremely vulnerable in this region and improved forecasts derived from the knowledge gained by this research may prevent the loss of life and property by educating forecasters and emergency responders concerning key precursor conditions. In addition, student interns from underrepresented communities will collaborate on this project at the NWS Forecast Office in Oxnard, California.

该研究项目试图更好地了解导致南加州日落风事件的机制。在没有非常强大的表面风速的情况下，日落风通常与极端加热有关。日落风会导致有利于毁灭南加州野火的条件，从而使它们非常重要且非常困难，这是由于它们的快速且非常出色的发作。要测试的基本假设跨越多种运动尺度：在较大的尺度（中α/β）下，日落风事件与：1）与上游沿海压力梯度驱动的低水平沿海喷气机有关ynez）。这种低水平的沿海喷气机由：1）在海岸海洋边界层附近的冷梯度和高架内陆，加热的对流边界层和2）沿海高表面压力（以这种热梯度的NNW的增强）在沿upstream Quret streak Streak的右出口区域增强。在较小的尺度（中伽马），波浪发育涉及内部重力波（IGW）沿沿海（圣伊内斯）山脉向西的插槽的破坏发展，从而触发了海上层上方的短期转子。转子放大器和断裂，将温暖和驱动器迅速混合到海洋层中。这种混合代表了快速日落变暖的第一个组成部分，因为冷船层消散并用残留的连续边界层的相对温暖的空气取代。此后，第二个组成部分很快发生了，随着IGW的尾随温暖池降临，形成中摩 - 伽马量表的沿海山脉下降，导致10-25c°的总变暖。在这项研究活动中进行的方法主要涉及数字建模，观察性数据分析和几个实际的实际和理想数据案例研究。将聘请天气研究和预测（WRF）模型，以模拟从极端到边际再到无效案例研究等众多日落风案例研究。这些事件将根据观察到的表面风阵和加热派系进行分类，数值建模将涉及一系列病例。在日落风的特定位置，水平网格的分辨率将从约10 km到〜666 m，具体取决于地形梯度的形状和幅度，从而允许该研究活动的智力优点的规模收缩。 结构。特别是，将对更大规模的喷气调整如何建立中尺度风和温度梯度来得出更详细的理解，这些梯度可能会受到地形的扰动，以产生中毛的山脉尺度山波，孔和尾流低。此外，在加利福尼亚州圣塔芭芭拉（Santa Barbara）附近的易火力区域中，海洋层，山波和较大规模的喷气式飞机如何相互作用。这项研究活动的广播公司影响将涉及该地区的天气预测进步，最值得注意的是在极端的野外危险中预测导致的条件。运营计算机模型无法模拟日落风的规模特征，这对于国家气象服务（NWS），私人预报员和当地应急人员来警告/准备火灾事件的情况更加困难。公众在该地区非常容易受到伤害，改善了从这项研究获得的知识中获得的森林人，可以通过对预报员和紧急响应者进行有关关键前体条件的教育，从而防止造成生命和财产的丧失。此外，来自代表性不足的社区的学生实习生将在加利福尼亚州奥克斯纳德的NWS预测办公室合作就此项目进行合作。