Drop-Size Distribution Observations from PECAN in Mesoscale Convective System Convective Regions

A critical goal of the Plains Elevated Convection At Night (PECAN) experiment is to improve scientific understanding of nocturnal mesoscale convective systems (MCSs). Microphysical processes in MCSs remain poorly understood in part due to the limited number of observational analyses of MCS drop-size distributions (DSDs), and that those analyses focused on a single subset of MCS types (mature leading line, trailing stratiform or LLTS MCSs). DSD characteristics need to be examined across a spectrum of different MCS archetypes, lifecycles, and environmental characteristics to obtain an improved understanding of MCS microphysical properties. To address this need, DSD data were collected during PECAN using three Parsivel disdrometers and over 30 hours of DSD data were obtained from 10 MCS cases encompassing different MCS archetypes and lifecycle stages across a wide geographic region.

Two convective line cases are analyzed to highlight contrasting MCS convective line DSD structure. For the 13 July 2015 Minnesota case, the leading line of the MCS was characterized by high concentrations of small drops. Remarkably, median volume diameters were smaller along the leading edge of the convective line than trailing stratiform regions in other MCSs. In contrast, the leading edge of the 6 July 2015 South Dakota MCS convective line contained moderate concentrations of large drops, consistent with past studies. A notable difference between the previously observed MCS structure and the 6 July 2015 MCS was a narrow convective band within the trailing stratiform region that produced the heaviest rainfall rates observed during the IOP. The analyses from the convective line cases will be composited to provide a more generalized view of MCS DSDs, and dual-polarization radar signatures associated with interesting DSD variability will be highlighted.