Department of Physics and Astronomy, College of Charleston, Charleston, South Carolina 29424, USA.
Department of Physics, Michigan Technological University, Houghton, Michigan 49931, USA.
Phys Rev Lett. 2018 Nov 16;121(20):204501. doi: 10.1103/PhysRevLett.121.204501.
The extent of droplet clustering in turbulent clouds has remained largely unquantified, and yet is of possible relevance to precipitation formation and radiative transfer. To that end, data gathered by an airborne holographic instrument are used to explore the three-dimensional spatial statistics of cloud droplet positions in homogeneous stratiform boundary-layer clouds. The three-dimensional radial distribution functions g(r) reveal unambiguous evidence of droplet clustering. Three key theoretical predictions are observed: the existence of positive correlations, onset of correlation in the turbulence dissipation range, and monotonic increase of g(r) with decreasing r. This implies that current theory captures the essential processes contributing to clustering, even at large Reynolds numbers typical of the atmosphere.
在湍流云中液滴聚集的程度在很大程度上仍未被量化，但这可能与降水形成和辐射转移有关。为此，利用机载全息仪器收集的数据来探索均匀层状边界层云中云滴位置的三维空间统计。三维径向分布函数 g(r) 清楚地表明了液滴聚集的证据。观察到了三个关键的理论预测：存在正相关、在湍流耗散范围内出现相关以及 g(r) 随 r 的减小而单调增加。这意味着，即使在典型的大气雷诺数下，当前的理论也能捕捉到导致聚集的基本过程。
