Numerical Simulations of Waves over Large Crater Topography in the Atmosphere

Abstract

Numerical simulations are used to investigate waves generated by flow over crater topography of diameter 100 km in an idealized atmosphere. The atmosphere is stratified with a constant buoyancy frequency profile and the background wind is constant. This study describes the development of a low-level jet along the upstream crater slope and its interaction with the cooler air within the crater valley. This interaction results in a hydraulic jump–like structure that acts as a modified topography, forcing a beam of secondary waves. The hydraulic jump is formed by a retreating gravity current as the cool air within the crater readjusts after the initial tilting of potential temperature contours. A two-dimensional simulation is used to compare features such as wave overturning in two and three dimensions. Several variations on the atmosphere’s profile are considered, including an atmosphere with reduced constant stratification and an atmosphere that is unstratified within the crater. These results indicate that the stratification within the crater is an important component in the development of the hydraulic jump. Also, several topographic modifications are included, such as a crater with no rims and a crater with reduced diameter. These comparisons reveal that the crater rims have little impact on the general wave pattern and that the crater curvature can influence wave breaking and lateral deflections. In addition, cases with rotation break the symmetry and induce more overturning in one-half of the crater.

Synoptic‐flow interaction with valley cold‐air pools and effects on cold‐air pool persistence: Influence of valley size and atmospheric stability

“…The CAP is progressively eroded by insolation after 0800 UTC, leaving only weak stability in the valley at 1100 UTC, which is subsequently removed as the CAP dissipates completely. Most of the above features are similar to aspects highlighted by Soontiens et al (2013) in their 3D simulations of a CAP within a large (40 or 100 km wide) enclosed crater (albeit in the absence of diurnal effects). In the absence of heat fluxes, Soontiens et al (2013) explain the return flow in terms of release of potential energy created by the initial displacement of the pool up the downwind slope.…”

“…Most of the above features are similar to aspects highlighted by Soontiens et al . () in their 3D simulations of a CAP within a large (40 or 100 km wide) enclosed crater (albeit in the absence of diurnal effects). In the absence of heat fluxes, Soontiens et al .…”

“…In the absence of heat fluxes, Soontiens et al . () explain the return flow in terms of release of potential energy created by the initial displacement of the pool up the downwind slope. However, in the present case, it is likely to be linked also to the drainage of air cooled adjacent to the valley wall, and the general accumulation of cold air in the growing, displaced CAP as it forms under nocturnal cooling.…”

“…An idealized 2D numerical approach is taken, confining the parameter space to spatial scale, background stability, and nocturnal net radiative loss. While other studies have addressed the dynamics of CAPs in large terrain, or the impact of changing valley scale or surface properties, these studies either do not consider a background wind (Katurji and Zhong, 2012;Kiefer and Zhong, 2013; or neglect diurnal effects (Soontiens et al, 2013;Lareau and Horel, 2015b;Rotunno and Lehner, 2017). The simulation methodology is discussed in the following section, results of the simulations presented in Section 3, with a discussion in Section 4 and conclusions in Section 5.…”

Turbulent Erosion of Persistent Cold-Air Pools: Numerical Simulations*

“…where U is the mean wind above the valley, N is the Brunt-Väisälä frequency, and H is the valley depth (Bell and Thompson 1980;Tampieri and Hunt 1985;Soontiens et al 2013). Using idealized tank experiments, Bell and Thompson (1980) demonstrate that when F $ 1:2, flow ventilates a valley regardless of the stratification.…”