Dynamics of Altocumulus Clouds

虽然对中层高积云的研究不如高层卷云或低层积云多，但据估计，中层高积云覆盖了地球表面的22%，对了解行星辐射平衡非常重要。 它们的特点是独特的物理过程，其中包括：（1）夹带到云底和云顶;（2）维持大规模的垂直运动;（3）冰和液相的频繁存在。 该项目旨在研究高积云的两个方面：造成其消散的机制和影响其结构水平变化的因素。 调查模式包括大涡模拟（LES），理论和数据分析。 用于验证模拟的观测来自1999年的复杂层状云实验（CLEX）。 模拟的目的是评估导致云消散的四个过程的相对重要性：大规模沉降，辐射加热，夹带干燥和降水沉降。 大涡模拟是使用Beowulf集群的22台个人电脑运行的区域大气模拟系统（RAMS）模型与先进的微物理治疗。 研究结果对气候模拟和云特性的遥感都有影响。

Though less studied than high-level cirrus or low-level stratocumulus clouds, mid-level altocumulus clouds are estimated to cover 22% of the earth's surface and to be important for understanding the planetary radiation balance. They are characterized by distinctive physical processes, which include (1) entrainment into both cloud base and cloud top; (2) maintenance by large-scale vertical motions; (3) the frequent presence of both ice and liquid phases. This project is aimed at studying two aspects of altocumulus clouds: the mechanisms responsible for their dissipation and the factors affecting the horizontal variability of their structure. Modes of inquiry include large-eddy simulation (LES), theory, and data analysis. Observations used for validating the simulations are from the Complex Layered-Cloud Experiment (CLEX) of 1999. The aim of the simulations is to evaluate the relative importance of four processes that lead to cloud dissipation: large-scale subsidence, radiative heating, entrainment drying, and precipitation fallout. The LES is carried out using a Beowulf cluster of 22 personal computers running the Regional Atmospheric Modeling System (RAMS) model with an advanced treatment of microphysics. Findings of the research bear on both climate modeling and remote sensing of cloud properties.