Mesoscale simulations are typically performed at coarse resolutions that do not adequately represent underlying topography; nesting large-eddy simulations within a mesoscale model can better resolve terrain and hence capture topographically-induced stable flow phenomena. In the case of the Mountain Terrain Atmospheric Modelling and Observations (MATERHORN) program, large temperature fluctuations were observed on the slope of Granite Peak, Utah, which partially encloses a cold-air pool in the east basin. These flow features are able to be resolved using large-eddy simulation within the Weather Research and Forecasting (WRF) model with $$\Delta x = 100$$ Δ x = 100 m, allowing accurate representation of lee vortices with horizontal length scale of $${\mathcal {O}}$$ O (1 km). At this resolution, terrain slopes become quite steep, and some model warm biases remain in the east basin due to limits on terrain-following coordinates that prevent the model from fully resolving drainage flows with this steep terrain. A new timestep limit for the WRF model related to these steep slopes is proposed. In addition, the initialization of soil moisture is adjusted by drying the shallowest layer to assist the formation of a cold pool in the large-eddy simulation. These real case simulations compare well to observations and also to previously published simulations using idealized configurations to study similar phenomena. For instance, the values of non-dimensional mountain height, which characterize flow regimes in idealized studies, are similar in the real case.

中文翻译：

---

Lee Vortices 对冷空气池位移的嵌套大涡模拟

中尺度模拟通常以不能充分代表底层地形的粗分辨率进行；在中尺度模型中嵌套大涡模拟可以更好地解析地形，从而捕获地形引起的稳定流动现象。在山地地形大气建模和观测 (MATERHORN) 计划的情况下，在犹他州花岗岩峰的斜坡上观察到大的温度波动，该斜坡部分包围了东部盆地的一个冷空气池。这些流动特征可以使用天气研究和预测 (WRF) 模型中的大涡模拟来解决，其中 $$\Delta x = 100$$ Δ x = 100 m，从而可以准确表示水平长度尺度为$${\mathcal {O}}$$ O（1 公里）。在这个分辨率下，地形坡度变得相当陡峭，并且由于地形跟随坐标的限制，一些模型的暖偏差仍然存在于东部盆地，这阻止了模型完全解析具有这种陡峭地形的排水流。提出了与这些陡坡相关的 WRF 模型的新时间步长限制。此外，通过干燥最浅层来调整土壤水分的初始化，以协助大涡模拟中冷池的形成。这些真实案例模拟与观察结果以及先前发布的使用理想化配置来研究类似现象的模拟相比效果很好。例如，在理想化研究中表征流态的无量纲山高值在实际情况中是相似的。