Main Causes of Morning Glory Cloud Occurrences

The Morning Glory cloud is a rare meteorological phenomenon consisting of a low-level atmospheric solitary wave and associated cloud, occasionally observed in different locations around the world. The wave often occurs as an amplitude-ordered series of waves forming bands of roll clouds.

Morning Glory Clouds Over Australia

The southern part of the Gulf of Carpentaria in Northern Australia is the only known location where it can be predicted and observed on a more or less regular basis due to the configuration of land and sea in the area.

 Morning Glory is likely to occur when the humidity in the area is high, which provides moisture for the cloud to form,

Causes

The Morning Glory cloud is not clearly understood because their rarity means they have little significance in terms of rainfall or climate. Regardless of the complexity behind the nature of this atmospheric phenomenon, some conclusions have been made about its causes. Through research, one of the main causes of most Morning Glory occurrences is the mesoscale circulations associated with sea breezes that develop over the peninsula and the gulf. On the large scale, Morning Glories are usually associated with frontal systems crossing central Australia and high pressure in northern Australia. Locals have noted that the Morning Glory is likely to occur when the humidity in the area is high, which provides moisture for the cloud to form, and when strong sea breezes have blown the preceding day.

Scenario for formation

Glider flying along the Morning Glory cloud formation in the Gulf of Carpentaria in northern Australia

The following is a summary of the conditions that cause the Morning Glory cloud to form in the Gulf of Carpentaria (after hypothesis of R.H.Clarke, as described in 1981). First,Cape York which is the peninsula that lies to the east of the gulf, is large enough that sea breezes develop on both sides. During the day, the breeze from the Coral Sea coast blows in from the east and the breeze from the gulf blows in from the west. The two breezes meet in the middle of the peninsula, forcing the air to rise there and form a line of clouds over the spine of the peninsula. When night comes, the air cools and descends and at the same time a surface inversion (where air temperature increases with height) forms over the gulf. The densities in this stable layer are different above and below the inversion. The air descending from the peninsula to the east goes underneath the inversion layer and this generates a series of waves or rolling cylinders which travel across the gulf. These cylinders of air roll along the underside of the inversion layer, so that the air rises at the front of the wave and sinks at the rear. In the early morning, the air is saturated enough so that the rising air in the front produces a cloud, which forms the leading edge of the cylinder, and evaporates in the back, hence forming the Morning Glory cloud. The cloud lasts until the surface inversion disappears with the heating of the day.

Burketown's Morning Glory

There are other ways in which Morning Glory clouds form, especially in rarer cases in other parts of the world, but these are far less understood.

Local weather lore in the area suggests that when the fridges frost over and the café tables' corners curl upwards at the Burketown Pub, there is enough moisture in the air for the clouds to form. Reportedly, all winds cease at ground level as the cloud passes over.
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