The Simulation of a Destructive Squall-Line Event: Sensitivity to Fundamental Microphysical Processes

The development of a classic squall-line event on July 10th, 2013 severely impacted Ohio and vicinity. Strong winds and lightning knocked out power over many locations, and power remained out for more than a day. The squall-line formed from the complex interactions of smaller convective storms and convective gust fronts.

We use Spectral (bin) Microphysics in WRF to examine the potential importance of difficult to simulate, but important microphysical processes of melting of ice hydrometeors and shedding of graupel and hail hydrometeors on squall line structure. Spectral (bin) Microphysics explicitly predicts the spectrum of liquid and hydrometeor sizes, as well as their interactions through collisions, and accurate fall velocities of each. The model is also sensitive to initial aerosol concentrations, as initial drop size formation and concentration depends on the availability of condensation nuclei.

We conclude i) that aerosol impacts on hail formation, and ii) melting and shedding are important physical processes that must be accurately represented in forecast models in order to capture complex interactions among convective lines (and or gust fronts) that lead to the development of these damaging weather systems.