Surge-bore systems can be traced at times from the eastern side of Cape York Peninsula, northern Australia, westward for distances of up to 700 km. In the process they are transformed from a sea-breeze surge to an undular internal bore. Bore formation over a strip of land near the west coast of the Peninsula is seen from observations to be due to the invasion of west coast sea-breeze air by an east coast sea-breeze surge. The observations indicate that the pre-conditioning conducive to bore genesis is due to the west coast sea-breeze. This greatly increases the critical velocity (phase speed of small amplitude long waves of the gravest mode) for waves moving towards the west-southwest. The two ways in which the sea-breeze achieves this result are by producing a strongly curved profile in the low-level wind component in this direction (gradient increasing with height) and also by increasing the depth of the near surface cooled layer. A gravity current from the east-northeast of sufficient depth impinging on such a pre-conditioned atmosphere is likely to produce an internal bore on the shallow boundary layer (about 1 km deep). Due to the lack of stratification above this layer, the bore is able to propagate undamped for great distances. This suggested mechanism accords in important respects with known facts, and explains why such events should be unusually common in this area of northern Australia. A similar mechanism explains the occasional occurrence of northward moving bores about the Gulf of Carpentaria coast when a synoptic scale pressure trough lies in the vicinity.
R. H. Clarke (Thu,) studied this question.