Scaling Properties of Cloud and Drizzle in Observed and Simulated Marine Stratocumulus

Clouds are inherently multiscale phenomena: cloud particles are typically microns to millimeters in characteristic length scale while the large-scale circulations that drive cloud systems can be many hundreds of kilometers across, a range of over 10 orders of magnitude. Limited computational power and the need to accurately represent large-scale circulations in numerical simulations of the atmosphere make explicit inclusion of cloud microphysics a practical impossibility. In the last 20 years, there has been a shift in regional and global atmospheric models toward scale-aware microphysical parameterizations with a statistical handling of the effects of subgrid variability. Despite this shift, many unanswered questions remain regarding the scaling characteristics of microphysical fields and how best to incorporate that information into parameterizations.

In this study, we diagnose the scaling properties of cloud and rain liquid water content from high frequency in situ observations and large eddy simulations (LES) of marine stratocumulus and find that both species exhibit scale invariance from the finest scales accessible to tens of kilometers. This implies that probability distribution function shape and cloud-rain covariance can be described as functions of length scale/model horizontal grid dimension. Despite finding scale invariance in both aircraft data and model output, the LES produces microphysical fields with markedly different scaling statistics than observed, suggesting that limited-area models are not able to adequately reproduce the spatial structure of precipitation.