Variability of continental stratiform clouds and its scale dependence based on millimeter-wave radar data

Characterization of subgrid-scale cloud structure and variability is important for mesoscale and climate models. We analyzed more than 1100 hours of radar reflectivity observations of continental low stratiform clouds over the ARM SGP site. The subgrid-scale variability was studied using the scale-by-scale analysis over the range from a several of hundreds meters up to ~200 km. The effect of precipitation on variability was studied by dividing all clouds into precipitating and non-precipitating category. In addition, we also contrasted variability of boundary layer clouds with that of low altitude stratiform clouds. Results show that precipitating clouds demonstrate on average much greater variability and longer long-term correlations compared to non-precipitating clouds. Variability for precipitating clouds significantly increases over the full scale range, indicating the existence of long–term correlations in precipitation and implying that mesoscale or synoptic forcings are important contributing factors in formation of cloud variability. Precipitation and variability are interdependent: the physical processes that favor greater variability may also enhance drizzle production. We hypothesize that scaling parameters of radar reflectivity may bear similarity to those of other cloud microphysical parameters, which are directly predicted by numerical models; therefore statistics of reflectivity variability may serve as a proxy for variability of cloud liquid water content or liquid water path.