This is a two-dimensional simulation of Kelvin-Helmholtz (KH) billows that form along an interface between two fluids of different densities owing to wind shear. In the panels below, cold air is propagating to the right, underrunning less dense warmer air. The vertical shear of the horizontal wind gives rise to KH billows. These billows form first near the leading edge of the cold air front and grow as they move rearward relative to the front.

This simulation was made using 50 m horizontal and vertical resolution. A 1 km tall block of cold air was placed at the surface at the initial time; it subsequently collapsed and spread along the surface. The environment is neutrally stratified. In the picture below, the colored field is temperature perturbation relative to the initial state, with a color interval of 0.3 K. The panels are separated by 1 min. Only a portion of the simulation domain is shown.

The animated GIF linked here presents a movie including the fields shown below.
The image is larger than 350Kb, so it may load slowly. The first time through, it may loop very slowly as the movie is loaded into memory. It will loop continuously.

Page created June, 1998, by Robert Fovell