Not Aussie dust, just our big nor'west arch

RED MASS: This stunning satellite shot highlights the nor'west arch that has blown out to the east of the South Island over the sea.

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It might look like the red Australian dust that blanketed Christchurch on Monday, but this stunning satellite shot taken that afternoon is actually highlighting the nor'west arch that has blown out to the east of the South Island over the sea.

Landcare Research remote sensing scientist David Pairman said "unfortunately" he doubted the red mass was anything other than thick cloud.

"I don't think it's dust to be honest. There may well be dust mixed in there, but usually dust is pretty thin and hard to pick unless it is a really thick layer."

The red tinge to the cloud mass was not a true colour but a thermal band that related to cloud temperatures of a certain coldness, which allowed weather forecasters to see how thick, and high, a cloud band was.

"That is showing up red because the cloud is quite high," he said.

- © Fairfax NZ News