This paper is concerned with the properties of complex propagating nonlinear tropospheric disturbances observed near Tennant Creek in the arid interior of the Northern Territory of Australia. Many of these unusual atmospheric disturbances resemble the well-known internal undular surges observed in the oceans and in inland stratified bodies of water. A description is presented of a wide variety of observations of solitary-wave-dominated evolving density intrusions, and it is shown that many of the features of these unique disturbances are in qualitative agreement with the predictions of nonlinear dispersive wave theory. In particular, it is shown that the evolutionary behavior of these disturbances is governed by the Benjamin-Ono equation and that intrusive motions of this type play an important role in the generation of boundary layer solitary atmospheric waves. Existing experimental evidence indicates that these disturbances originate primarily in the interaction of katabatic flows, propagating sea breeze vortices, and 'morning glory' phenomena with the stably stratified nocturnal radiation inversion.