Microphysical Aspects of Cumulus Clouds

在云的视觉识别中，云层周围的多云空气和较干燥的空气之间发生了活跃的混合。最近对层积云夹带的观察提供了证据，证明干空气主要是从云顶进入，而不是从侧边界进入。目前，对夹带的机理还不完全清楚。夹带的体积，加上来自上方的更凉爽和更干燥的空气，稀释了云层中的空气，产生了负浮力，因此在云层内下降。根据现场观测和实验室实验，被卷带的气团被认为表现为球状涡旋，气团中间有强烈的上升气流，而外围上升或下降的空气较慢。根据这笔赠款，特尔福德教授将研究湍流球形涡旋的动力学，并将其应用于云模型。由于卷吸过程可能在解释积云的有限寿命和预测世界各地观测到的各种云滴尺寸谱方面发挥重要作用，特尔福德教授的新理论如果得到成功测试，将是对云模型的重大贡献。

Within the visual identification of clouds, active mixing takes place between the cloudy air and the drier air of its environment. Recent observations of stratocumulus entrainment provide evidence that dry air mostly enters from the cloud top instead of from the lateral boundaries. At present, the entrainment mechanism is not fully understood. The entrained volume, with the cooler and drier air from above, dilutes the cloudy air, is negatively buoyant, and therefore descends within the cloud. Based on field observations and laboratory experiments, the entrained blob of air is envisioned to behave like a spherical vortex, with strong updraft in the middle of the blob and slower rising or descending air around the periphery. Under this grant, Profesor Telford will examine the dynamics of a turbulent spherical vortex and implement it in a cloud model. Since the entrainment processes may play a significant role in explaining the finite life time of cumulus clouds and in predicting various cloud drop size spectra observed around the world, Professor Telford's new theory, if successfully tested, will be a major contribution to cloud modelling.