Morning Glory cloud

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Map of Australia, the Gulf of Carpentaria can be found in northern Australia
Map of Australia, the Gulf of Carpentaria can be found in northern Australia
Satellite photo of a Morning Glory cloud over the Gulf of Carpentaria
Satellite photo of a Morning Glory cloud over the Gulf of Carpentaria

The Morning Glory cloud is a rare meteorological phenomenon observed in Northern Australia's Gulf of Carpentaria. A Morning Glory cloud is a roll cloud that can be up to 1000 kilometers long, 1 to 2 kilometers high, and can move at speeds up to 60 kilometers per hour. The morning glory is often accompanied by sudden wind squalls, intense low-level wind shear, a rapid increase in the vertical displacement of air parcels, and a sharp pressure jump at the surface. In the front of the cloud, there is strong vertical motion that transports air up through the cloud and creates the rolling appearance, while the air in the middle and rear of the cloud becomes turbulent and sinks. The cloud can also be described as a solitary wave or a soliton, which is a wave that has a single crest and moves without changing speed or shape.

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[edit] Causes

Despite being studied extensively, the Morning Glory cloud is not clearly understood. Regardless of the complexity behind the nature of this atmospheric phenomenon, some conclusions have been made about the causes of the cloud. Through research, one of the main causes of most Morning Glory occurrences are due to 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 conditions ripe for the formation of the Morning Glory is for high humidity in the area, which provides moisture for the cloud to form and for strong sea breeze winds to be blowing the day before.

[edit] Scenario for formation

The following is a summary of the conditions that cause the Morning Glory cloud to form in the Gulf of Carpentaria. 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. 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 and forces the air to rise there and a line of clouds form over the spine of the peninsula. When night comes, the air cools and descends and at the same time a surface inversion forms over the gulf (where the air as you go up in height becomes warmer rather than cooler). 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 generates a wave or series of waves and travels across the gulf like ripples in a lake. The air rises in the front of the wave and sinks in 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 wave, and evaporates in the back... hence forming the Morning Glory cloud. The cloud lasts until the surface inversion is burned off by the heating of the day. This scenario describes the most common way in which the Morning Glory cloud forms. There are other ways in which they form, especially in rarer cases in other parts of the world, but these are far less understood. Similar phenomena also occur over the Central United States, the English Channel, over Berlin, Germany, Eastern Russia, as well as other maritime regions of Australia, but only the ones over Burketown are predictable at a certain time of year. Local weather lore in the area suggests that when the fridges frost over and the café tables' corners curl upwards at the Burkestown 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. [1]

The best vantage point to see Australia's Morning Glory is from Burketown in the remote Far North Queensland around September and October. Towns in this part of the world are small and a long way apart, and Burketown has an influx of glider and hang-glider pilots at this time of year.

Similar spectacular Morning Glory type roll clouds have also been reported to occasionally happen off the Mexican coast in the Sea of Cortez. The phenomenon has also been observed from Sable Island, a small Canadian island located 180 km southeast of Nova Scotia. In contrast to Australia’s Gulf of Carpentaria where the Morning Glory cloud is visible in the morning, the cloud has a predilection to hit the island in the early evening. Rare examples have been observed via satellite observation over the Joseph Boneparte Gulf in the Eastern Kimberley region of Australia as well as over the Arabian Sea.

[edit] References

  1. ^ The Cloudspotter's Guide, Gavin Pretor-Pinney, 2006, ISBN 0-340-89589-6

[edit] External links

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