Tasmanian mountains create cool clouds

Ben Domensino, 31 July 2019

Tasmania's mountains created some impressive cloud formations on Wednesday.

A small spiral of cloud could be seen passing to the north of Tasmania during Wednesday, rolling from west to east across Bass Strait. This spiral was caused when air approaching Tasmania from the west was forced to pass around the state's mountainous terrain.

Image: A small cloud vortex near northern Tasmania on Wednesday.

Another small circulation of cloud could be seen off the state's east coast, briefly spinning in the opposite direction.

The formation of these 'eddies' downwind of Tasmania is a process called vortex shedding and it occurs near other mountainous islands around the world. 

Vortex shedding can lead to a bizarre cloud formation called a Kármán vortex street, or von Kármán vortices. This rare phenomena occurs when a repeating pattern of cloud vortices, or spirals, forms downwind of an island.

Image: von Kármán vorticies off Madeira and Canary Islands in 2010. Source: NASA Aqua/MODIS

Another notable feature of the clouds near Tasmania on Wednesday was that they only covered the western side of the island. This is a common effect when westerly winds pass over the state. Air rising up the western side of the state's mountains cause clouds to form, while the air flowing downslope in the state's east is too dry to cause cloud. This process is called the foehn effect and it's why western Tasmania has seen so much more rain than eastern Tasmania this month.