Dynamics of Altocumulus Clouds

虽然与高层卷云或低层层积云相比，对中层高积云的研究较少，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很重要。它们具有独特的物理过程，包括：(1)夹带进入云底和云顶；(2)大规模垂直运动维护；(3)冰相和液相的频繁存在。本项目旨在研究高积云的两个方面：高积云消散的机制和影响其结构水平变率的因素。探究模式包括大涡模拟（LES）、理论和数据分析。用于验证模拟的观测数据来自1999年的复杂分层云实验（CLEX）。模拟的目的是评估导致云耗散的四个过程的相对重要性：大尺度沉降、辐射加热、卷带干燥和降水沉降。LES是使用一个由22台个人计算机组成的Beowulf集群进行的，该集群运行区域大气模拟系统（RAMS）模式，并进行了微物理的高级处理。研究结果对气候模拟和云特性遥感都有影响。

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.