Statistics of Small-Scale Velocity Fluctuations and Internal Intermittency in Stratocumulus Clouds

Clouds are known to be turbulent but the details of their internal turbulent structure have been largely unexplored. Measurements of turbulent velocities in stratocumulus clouds reveal an intermittent structure consistent with that observed in classic homogeneous isotropic turbulence. The measurements were taken using a hotwire anemometer on the helicopter-borne ACTOS measurement system. Hotwire signal artifacts resulting from droplet impacts are removed without significantly degrading the signal, such that high-order velocity structure functions can be evaluated. The structure function analysis for orders 2 through 8 show statistically significant departures from the Kolmogorov 1941 scaling, yielding scaling exponents consistent with the Kolmogorov-Obukhov refined similarity hypothesis with an intermittency exponent of 0.25. We find no evidence of any departure from the large body of knowledge obtained from the laboratory on the fine scale turbulence structure. This suggests that processes depending on the fine-scale structure of turbulence that cannot presently be measured in clouds can be explored in the laboratory setting.