Expansion of a Holepunch Cloud by a Gravity Wave Front

Abstract

A holepunch cloud is a curious phenomenon where a disturbance in a thin cloud layer initiates an expanding circular hole of clear air. Usually triggered by the passage of aircraft, observations of these holes in clouds date back to the earliest days of aviation, but only recently has a holepunch cloud been simulated within a fullphysics numerical model. These computations confirm that ice crystal growth through the WegenerBergeron-Findeisen process creates a small cloud-free region whose subsequent outward spread defines the holepunch. The mechanics behind this continued expansion, however, has yet to be definitively identified. In this article, the motion of the cloud edge is explained as a propagating gravity wave front. To support this idea, a hierarchy of three idealizations is analyzed: a full-physics numerical model, a fluid mechanical model with simplified moisture effects, and a conservation law analysis for front motion. The essence of the holepunch cloud is established to be a moist air layer that is unsaturated (clear) and weakly stratified within the hole but saturated (cloudy) and moist neutral outside of it. The cloud edge thus represents a barrier to the outward propagation of gravity waves within the clear air-the result of this collision is a wave front whose velocity determines the growth rate of the hole.

Anthropogenic Aerosol Influences on Mixed-Phase Clouds

“…This process is called the Wegener-Bergeron-Findeisen (WBF) process [4,21,100]. The result of this process can be observed in so-called hole punch clouds [30,71] (Fig. 1), where in the wake of an aircraft penetrating the supercooled liquid cloud, locally the temperature decreases sufficiently for ice formation.…”

Dynamical Response of an Arctic Mixed‐Phase Cloud to Ice Precipitation and Downwelling Longwave Radiation From an Upper‐Level Cloud

“…The processes described here share some similarities with, but are different from, those in the hole‐punch cloud discussed by Heymsfield et al () and Muraki et al (). In our case, the perturbations were sufficiently slow so that many other processes, including radiation, turbulence, and even subsidence, played a role in shaping the thermally driven circulation.…”

“…Moreover, Figure 4(d) shows that the excess from the evaporation of liquid (magenta line) was much greater in magnitude than the deficit caused by ice growth (green line) for most of the cloud depth. Both Heymsfield et al (2011) and Muraki et al (2016) rejected ice microphysical processes at liquid cloud edge as a cause for the observed expansion of the cloud hole by showing that the evolution of the cloud hole was not altered in sensitivity simulations where the latent heating from ice was limited to the seeded region. In our simulation, the seeded ice particles fell out of the outflow quickly.…”

“…We hypothesize that the ice-seeding and the DLR from the upper-level cloud will result in horizontal heterogeneity in cloud properties and heating rates in the lower-level liquid cloud layer and that the differential heating may drive mesoscale circulations in that cloud layer. Heymsfield et al (2011) showed that when a supercooled altocumulus layer glaciates from ice particles induced rapidly by aviation activities, the circulation generated by the latent heating from ice particle growth can further clear the remaining liquid cloud layer, a phenomenon later explained by Muraki et al (2016) as the propagation of a gravity wavefront outward from the initial gap. Similar organized circulations could deplete liquid in the lower-level cloud in response to ice-seeding and DLR from an upper-level cloud.…”