The Morning Glory: An extraordinary atmospheric undular bore

Observations made during an expedition in October 1980 to study ‘morning glory’ wind squalls in the Gulf of Carpentaria region of northern Australia are described. During a ten day period in Burketown, North Queensland, six squalls were documented on consecutive mornings (8–13 October), including two moving from the south, an apparently unusual direction. The unique data gathered from the latter confirm that these have the same character as their north‐easterly counterparts; that is, they are undular bores. The origin of southerly glories remains uncertain, but, at least, in some cases, appears to be linked with the northeast advance of a frontal trough across central Australia. While the data are equivocal, it seems possible that the motion of the front into the developing nocturnal inversion could generate waves, or hydraulic‐type disturbances, which run along the inversion layer, ahead of the front, as proposed by Tepper (1950). The efficacy of such a mechanism is demonstrated by a simple laboratory experiment. Evidence is presented which suggests that morning glory type events occur elsewhere in the world, sometimes as precursors to cold fronts. Observations in the Gulf of Carpentaria region show that they are effective triggers of deep convection when they advance into air with a sufficient degree of conditional instability.