PIMS - CSC Seminar: Dave Muraki

A holepunch cloud is a curious phenomenon where a disturbance in a thin cloud layer, as can be caused by ascending or descending aircraft, results in a growing circular hole of clear air. Observed since the dawn of aviation, only in 2011 was this holepunch feature simulated in a full-physics numerical weather model. Although the initiation process has been clearly attributed to ice crystal formation, we explain the continued expansion of the hole as a fluid dynamical wave.

In particular, the cloud edge is shown to be a travelling front between two phases of moist air — unsaturated and weakly-stratified (clear) intruding into saturated and moist-neutral (cloudy). This talk outlines how the fluid mechanics (and thermodynamics) for moist, densitystratified air can be simplified to PDE systems from which we can extract a mathematical understanding of cloud edge motions. In the case of the holepunch cloud, the result is a non-hyperbolic conservation law system that possesses travelling discontinuities that satisfy Rankine-Hugoniot conditions, despite the absence of underlying characteristics. This work is in collaboration with two NCAR scientists, R. Rotunno and H. Morrison.