标题： 湍流、重力和非连续流体力学相互作用对云中液滴尺寸分布的影响 显示英文标题

标题： The effect of turbulence, gravity, and non-continuum hydrodynamic interactions on the drop size distribution in clouds

摘要： 云中微米级液滴的演化被研究，重点在于15-40 $\mu m$ 半径的“尺寸间隙”区域，在此区域内凝结和差分沉降在促进生长方面效果最差。 这一瓶颈导致生长模型不准确，而湍流可能能纠正与现场云测量结果之间的不一致。 详细分析了湍流碰撞、液滴混合和水蒸气波动在跨越“尺寸间隙”中的作用。 由湍流剪切和差分沉降耦合效应驱动的碰撞被证明可以增长雨滴大小的液滴。 湍流引起的水蒸气波动也促进了生长，这些波动在初始由凝结驱动的生长过程中保持多分散性，并通过由差分沉降驱动的聚并促进后续生长。 液滴的碰撞率受到非连续流体力学的强烈影响，因此在凝结区域之外的尺寸演化对空气的平均自由程非常敏感。 湍流引起的惯性聚集导致生长速率适度增强，但湍流剪切率的间歇性并未显著改变聚并速率。 通过使用一种能够捕捉湍流间歇性和混合的蒙特卡洛方案，在绝热上升的空气团中演化大量液滴，评估了所有这些现象的耦合影响。 显示英文摘要

摘要： The evolution of micron-sized droplets in clouds is studied with focus on the 'size-gap' regime of 15-40 $\mu m$ radius, where condensation and differential sedimentation are least effective in promoting growth. This bottleneck leads to inaccurate growth models and turbulence can potentially rectify disagreement with in-situ cloud measurements. The role of turbulent collisions, mixing of droplets, and water vapour fluctuations in crossing the 'size-gap' has been analysed in detail. Collisions driven by the coupled effects of turbulent shear and differential sedimentation are shown to grow drizzle sized droplets. Growth is also promoted by turbulence-induced water vapour fluctuations, which maintain polydispersity during the initial condensation driven growth and facilitate subsequent growth by differential sedimentation driven coalescence. The collision rate of droplets is strongly influenced by non-continuum hydrodynamics and so the size evolution beyond the condensation regime is found to be very sensitive to the mean free path of air. Turbulence-induced inertial clustering leads to a moderate enhancement in the growth rate but the intermittency of the turbulent shear rate does not change the coalescence rate significantly. The coupled influence of all these phenomena is evaluated by evolving a large number of droplets within an adiabatically rising parcel of air using a Monte Carlo scheme that captures turbulent intermittency and mixing.