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Improvement of Atmospheric Objective Analysis Over Sloping Terrain and Its Impact on Shallow‐Cumulus Clouds in Large‐Eddy Simulations
Journal of Geophysical Research: Atmospheres ( IF 3.8 ) Pub Date : 2020-05-29 , DOI: 10.1029/2020jd032492
Shuaiqi Tang 1 , Shaocheng Xie 1 , Minghua Zhang 2 , Satoshi Endo 3
Affiliation  

Surface topography strongly impacts the regional atmospheric circulation dynamically and thermodynamically. Over the Great Plains in the United States, the gently tilted slope is an important factor that impacts clouds, convection, and regional circulations. This study enhances an atmospheric constrained variational analysis by using a terrain‐following sigma vertical coordinate and applies to the data collected at the Southern Great Plain (SGP) site of the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program. Sensitivity studies are performed to examine the impact of the terrain effects on the derived large‐scale atmospheric forcing fields and the simulated shallow‐cumulus clouds in large‐eddy simulation (LES) driven by the forcing. We found that the terrain impacts on the large‐scale forcing fields are mainly at lower levels and are strongly controlled by up/downslope winds. The response of the derived forcing to the slope of the terrain is monotonic, but the response of the simulated shallow‐cumulus clouds is more complex and depends on several factors. Overall, the terrain impact is small over SGP due to the small slope angle. However, the flat‐surface assumption may cause larger biases in the large‐scale forcing fields at locations with steeper terrain. The new sigma coordinate algorithm, with its consideration of surface slope, should be more suitable to derive large‐scale objective analysis over regions with steep terrain for application to force single‐column models, cloud resolving models, and LES models.

中文翻译:

大涡模拟中倾斜地形大气目标分析的改进及其对浅积云的影响

地表地形动态地和热力地强烈影响区域大气环流。在美国大平原上,缓倾斜的坡度是影响云,对流和区域环流的重要因素。这项研究通过使用地形跟随sigma垂直坐标来增强大气约束的变化分析,并将其应用于在能源部(DOE)大气辐射测量(ARM)计划的南部大平原(SGP)站点收集的数据。进行了敏感性研究,以研究在强迫作用下的大涡模拟(LES)中,地形效应对衍生的大尺度大气强迫场和模拟浅积云的影响。我们发现,地形对大型强迫场的影响主要在较低的水平上,并且受到上/下坡风的强烈控制。得出的强迫对地形坡度的响应是单调的,但模拟的浅积云的响应则更为复杂,并且取决于多个因素。总体而言,由于倾斜角较小,因此与SGP相比地形影响较小。但是,平坦的假设可能会在地形较陡的位置对大型强迫场造成较大的偏差。新的sigma坐标算法考虑了表面坡度,应该更适合在具有陡峭地形的区域上进行大规模客观分析,以应用于强制单列模型,云解析模型和LES模型。得出的强迫对地形坡度的响应是单调的,但是模拟的浅积云的响应则更为复杂,并且取决于多个因素。总体而言,由于倾斜角较小,因此与SGP相比地形影响较小。但是,平坦的假设可能会在地形更陡峭的位置对大型强迫场造成较大的偏差。新的sigma坐标算法考虑了表面坡度,应该更适合在具有陡峭地形的区域上进行大规模客观分析,以应用于强制单列模型,云解析模型和LES模型。得出的强迫对地形坡度的响应是单调的,但是模拟的浅积云的响应则更为复杂,并且取决于多个因素。总体而言,由于倾斜角较小,因此与SGP相比地形影响较小。但是,平坦的假设可能会在地形较陡的位置对大型强迫场造成较大的偏差。新的sigma坐标算法考虑了表面坡度,应该更适合在具有陡峭地形的区域上进行大规模客观分析,以应用于强制单列模型,云解析模型和LES模型。由于倾斜角较小,SGP上的地形影响较小。但是,平坦的假设可能会在地形更陡峭的位置对大型强迫场造成较大的偏差。新的sigma坐标算法考虑了表面坡度,应该更适合在具有陡峭地形的区域上进行大规模客观分析,以应用于强制单列模型,云解析模型和LES模型。由于倾斜角较小,SGP上的地形影响较小。但是,平坦的假设可能会在地形更陡峭的位置对大型强迫场造成较大的偏差。新的sigma坐标算法考虑了表面坡度,应该更适合在具有陡峭地形的区域上进行大规模客观分析,以应用于强制单列模型,云解析模型和LES模型。
更新日期:2020-07-05
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