Abstract
The reflection of a wave at a fluid interface is fundamental to the atmospheric wave duct. As latent heating distinguishes the buoyancy response between cloudy and clear air, cloud edges can serve as a ducting interface for gravity waves. However, advection of the thermodynamic conditions by the ducted wave itself can cause evaporation or condensation, where the motion of cloud edges results from shrinking or enlarging regions of saturated air. For an idealized ducted-wave mode trapped by a cloud layer, a linear Boussinesq analysis shows that its vertical motions produce a sinusoidal corrugation of the cloud edge that travels with the wave. When thermodynamic conditions are continuously varying, the cloud edge propagates as the moving onset of phase change, and not as a material interface. Using this Boussinesq solution to initialize the full-physics CM1 model, the simulation confirms the amplitude and speed of the cloud-edge wave. In a comparison of simulations for domains of decreasing height, a convergence to the Boussinesq ducted wave can be quantitatively established. This demonstration suggests a theory-based convergence benchmark for the motion of a cloud edge by phase change.
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