On the Use of an Explicit Microphysical Model to Investigate the Temporal and Spatial Evolution of Rainfall Microphysics in Different Storm Environments

Two Micro Rain Radars (MRRs) were deployed in the Southern Appalachians during the summer and fall seasons of 2012, in ridge and valley locations in the French Broad River Basin. The radars were collocated with Hydrological Services tipping bucket rain gauges at 0.1 mm resolution, Vaisala automated weather stations and Parsivel optical disdrometers. This study augments others conducted in previous years during the months May - September in ridge and valley locations in the Pigeon River Basin, and ridge-ridge studies across both basins. Observations from the vertically pointing radar are used to provide boundary conditions for an explicit raindrop population dynamics model, which solves the stochastic collection-breakup equation, in order to model the evolution of microphysical properties (drop size distribution, rain intensity and hydrometeor type) through time and space and gain insight into the processes (autoconversion, overarching synoptic conditions, terrain contributions) that drive this evolution. Surface observations from the disdrometers and rain gauges are used to investigate the model results. Observations from a spatially dense, high elevation rain gauge network are also used to further define storm structure. Results show significant variability in precipitation intensities and accumulations along the ridge line as well as suggest the localized importance of persistent fog interacting with low level cloud to intensify or trigger precipitation events that are often experienced only at high elevations and contribute significantly to the yearly water budget of the region. A period of cross calibration with both MRRs, Parsivel disdrometer models 1 and 2, automated weather stations and tipping bucket rain gauges (during May/early June 2012) is used to examine questions of uncertainty with regard to measurement scale. Last, the results from using this model at other locations during ground validation campaigns (TWP-ICE, MC3E) are compared with the findings from modeling storms in the Southern Appalachians in order to point out overarching conclusions that can be made about precipitation evolution in different storm type and terrain type.