The Effect of Ambient Stratification and Moisture on the Motion of Atmospheric Undular Bores

Abstract

A numerical model is used to examine the effects of ambient stratification on the behavior of an atmospheric undular bore. It is shown that stratification reduces the amplitude of the disturbance at low levels by allowing energy to propagate upward. This reduction of amplitude can be inhibited by specifying winds opposing the wave motion in the middle and upper troposphere. Mean observations in the region where the Morning Glory is prevalent support this result. The effects of moisture are also examined. If condensation does not occur, moisture increases the disturbance amplitude by reducing, through virtual temperature effects, the stability of the atmosphere. However, if condensation occurs, the wave amplitude is decreased compared with a dry atmosphere with the same effective stability. Finally, it is shown that cloud formation increases the wavelength of the disturbance.