Atmospheric Internal Solitary Waves

The solitary waves that have been observed in the atmosphere fall broadly into two classes: those that propagate in a fairly shallow stratified layer near the ground and those that occupy the entire troposphere. We present a survey of the observations of both types of solitary waves. The generation mechanisms differ substantially for these two types of solitary waves. Those that propagate in a shallow stratified layer are generated by small scale or mesoscale phenomena such as thunderstorm outflows, sea breezes or katabatic winds. Those solitary waves that occupy the entire troposphere are generated by much larger scale phenomena, such as some kind of geostrophic adjustment process. We also review the previous attempts that have been made to compare these observations with weakly nonlinear solitary wave theory. It appears that models with a deep passive upper layer are generally not applicable, while Korteweg-de Vries models, perhaps enhanced with higher-order nonlinearity, provide the best comparison; but it remains unclear what constitutes a suitable upper boundary condition.