Across the Gulf of Carpentaria in Queensland, Northern Australia, a remarkable cloud formation called the Morning Glory can appear in the skies between late September and early October. The cloud is manifest as a cylinder, or series of cylinders, hovering roughly 500 m above the ground, looking like tornados on their side, rolling above the flat desert landscape at a speed of around 50 km/h.1 The roll clouds are around 1000 m high and stretch for 1000 km across the sky, typically oriented from southeast to northwest. The particular Morning Glory featured in our photos displayed in Figures 1 and 2, taken during our field study on September 28th, 2012, is highlighted by the yellow box in the corresponding satellite image of Australia in Figure 3(a).
Aerial photographs of the Morning Glory cloud lines on September 28, 2012 taken near Burketown, southwest of the Gulf of Carpentaria coast. All views are looking southeast along the wave front.
Aerial photographs of the Morning Glory cloud lines on September 28, 2012 taken near Burketown, southwest of the Gulf of Carpentaria coast. All views are looking southeast along the wave front.
(a) Satellite image of the Morning Glory cloud observed on September 28, 2012, south of Burketown. The cloud is highlighted by the yellow box (Image: Geostationary Meteorological Satellite, Japanese Meteorological Association). (b) Schematic illustrating the formation of the Morning Glory roll cloud. The up-draft at the leading edge of an atmospheric solitary wave, on the interface between moist and dry air, raises moist air above the condensation level, forming cloud; the cloud disappears in the down-draft at the trailing edge of the wave, where the moist air descends below the condensation level.
(a) Satellite image of the Morning Glory cloud observed on September 28, 2012, south of Burketown. The cloud is highlighted by the yellow box (Image: Geostationary Meteorological Satellite, Japanese Meteorological Association). (b) Schematic illustrating the formation of the Morning Glory roll cloud. The up-draft at the leading edge of an atmospheric solitary wave, on the interface between moist and dry air, raises moist air above the condensation level, forming cloud; the cloud disappears in the down-draft at the trailing edge of the wave, where the moist air descends below the condensation level.
Further aerial photographs of the Morning Glory cloud lines on September 28, 2012 taken near Burketown. From left-to-right, views are from behind the wave, looking northwest along the wave front, and looking back at three daughter waves crests behind the leading wave, respectively.
Further aerial photographs of the Morning Glory cloud lines on September 28, 2012 taken near Burketown. From left-to-right, views are from behind the wave, looking northwest along the wave front, and looking back at three daughter waves crests behind the leading wave, respectively.
Morning Glory clouds are visible manifestations of atmospheric solitary waves. As illustrated in Figure 3(b), in the case of Morning Glory clouds the waves propagate on the sharp interface between a layer of moist air, brought in by sea breezes the night before, and the much drier ambient air that sits above it. As the wave travels, cloud is created continuously in the up-draught along the leading edge as moist air is lifted to the condensation level, where it forms cloud; the cloud subsequently evaporates on the down-draft at the trailing edge of the wave, as it descends below the condensation level. This process provides a striking means of visualizing a solitary wave, all courtesy of Mother Nature.