The Role of Turbulent Layers on Microphysical Enhancement Inferred From SNOWIE Observations

Abstract

Fine turbulent layers are ubiquitous in orographic clouds, midlatitude cyclones, and any sheared or conditionally buoyant mesoscale environments. Their role on cloud microphysics has been indirectly inferred from coarse resolution ground-based radar, idealized or high-resolution research model simulations, and laboratory wind tunnel and cloud chamber studies. This dissertation presents a comprehensive analysis of their role on clouds observed over the course of the Seeded and Natural Orographic Wintertime clouds—the Idaho Experiment (SNOWIE) field campaign. The analysis includes both detailed case studies of aircraft in-situ dynamics and microphysics data and statistical analysis of high-resolution vertical cloud radar profiles to trace the microphysical development of orographic layer clouds where turbulent layers where observed. Part of this analysis develops a novel method for attributing radar pulse-pair Doppler spectrum width measurements to air motion turbulence, corroborated against both in situ and coarse resolution mean Doppler motion data. Combined over the course of the entire SNOWIE campaign dataset, case studies and column-averaged radar vertical profiles in the vicinity of these turbulent layers provide insight into the comparative hydrometeor growth enhancement collocated with these layers, some context for the mechanisms of this vertical growth enhancement relative to quiescent conditions, and insight into the shortfalls of current generation forecast modeling parameterizations of microphysics and turbulence linkages. The final relative vertical growth enhancement over the entire field campaign for embedded layers of turbulence compared to nearby quiescent regions is a median reflectivity increase with downward distance of 13.1 dBZe/km (1.8 to 23.0 with 95% computed confidence).