Examining Microburst Scaling Relationships Through Full-Physics Large Eddy Simulations

A microburst is a meteorological phenomenon comprising of sinking air below a thunderstorm cloud base that spreads out laterally as it reaches the ground. The resultant outflow is capable of producing severe winds near the surface and extreme shear aloft. The source of this sinking air is two-fold: air is dragged down from hydrometeor loading, and/or the air is cooled from the evaporation or sublimation of hydrometeors produced by the storm resulting in a denser air mass compared to the surrounding environmental air. For decades, microbursts have been simulated in laboratory experiments and with numerical models. The laboratory experiments typically consisted of releasing a denser fluid into a volume of a less dense, ambient fluid, while the numerical experiments ranged from simplified two-dimensional models to three-dimensional large-eddy simulations (LES).

The pioneering laboratory experiments done in the early 1990's by the fluid mechanics community presented scaling relationships for microbursts which held remarkably well between tank experiments, observed radar data, and idealized numerical models. However, none of the past numerical studies, to our knowledge, have utilized models that consider processes such as radiation, microphysics, and turbulence that drive microbursts in their simulations. In this study, the microburst scaling relationships are explored in a full-physics meteorological numerical model, Cloud Model 1 (CM1).