Turbulence in the Long-lived, Very Stable Atmospheric Boundary Layer

在山区地形的夜间或陆地上寒冷的季节，经常观察到大气的稳定条件。在极地地区，稳定的天气状况会持续数天，这是一种长期存在的天气状况。更好地了解稳定条件下的大气流动是极地冰盖质量平衡、气候模拟、地形降水、雾形成、严重下坡风暴和相关飞机湍流等领域取得进展的关键。尽管对大气中稳定条件进行了大量的理论、计算和实验研究，但在数值天气预报（NWP）模式中准确地表示大气中的稳定条件仍然是一项具有挑战性的任务。对湍流混合的过高或过低估计会在气象建模的其他方面产生意想不到的后果，例如对强风和降水的错误预测。该项目旨在更好地理解长期稳定条件下的湍流，并为其在计算机模型中的数学表示开发可靠的理论，预计这将为更准确的天气预报和气候预测铺平道路，减少不确定性。 该项目的科学目标将通过在表面冷却通量和恒定的环境分层的联合作用下对埃克曼层中的湍流进行密集的直接数值模拟来实现。该配置是在极地地区观察到的长寿命大气边界层的理想化，不同于仅用表面冷却模拟稳定的埃克曼层的常见方法。该项目将量化扩展的无量纲参数空间对湍流的影响。该项目将扩展和完善长期稳定的埃克曼层的相似性理论和相关性。预计在投影完成时，将有一个定量分类方案来解释稳定边界层中湍流的全球不稳定性。该项目将为现有的开源谱/hp元素流解算器贡献一个大气边界层模块，并为本科生提供计算科学和高性能计算方面的研究经验。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Stable conditions of the atmosphere are frequently observed during nighttime in mountainous terrain or during cold seasons over land. Stable conditions persist for days as a long-lived weather regime in polar regions. A better understanding of atmospheric flows under stable conditions is key for advances in areas such as mass balance of polar ice sheets, climate modeling, orographic precipitation, fog formation, severe downslope windstorms, and associated aircraft turbulence. Despite numerous theoretical, computational, and experimental investigations of stable conditions in the atmosphere, its accurate representation in numerical weather prediction (NWP) models remains to be a challenging task. Over or under estimation of turbulent mixing is known to create unintended consequences in other aspects of meteorological modeling, such as incorrect predictions of stronger winds and precipitation. This project aims to better comprehend turbulence in long-lived, stable conditions and develop a reliable theory for its mathematical representation in computer models, which is expected to pave the way to more accurate weather forecasts and climate projections with reduced uncertainties. The scientific objectives of the project will be achieved through intensive direct numerical simulations of turbulence in the Ekman layer under the joint action of a surface cooling flux and a constant ambient stratification. The configuration is an idealization of long-lived atmospheric boundary layers observed in polar regions and differs from the common approach of simulating stable Ekman layers with surface cooling only. The project will quantify the effects of an expanded dimensionless parameter space on turbulence. The project will extend and refine similarity theories and correlations for long-lived stable Ekman layers. A quantitative classification scheme to account for the global intermittency of turbulence in stable boundary layers is expected at projection completion. This project will contribute an atmospheric boundary layer module to an existing open source spectral/hp element flow solver and provide research experiences in computational sciences and high-performance computing to undergraduate students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.