Waves break over Mosgiel

These spiral-like clouds (just above the power lines), photographed at Mosgiel last Saturday, are quite rare. Photo by Ruth Thompson.
These spiral-like clouds (just above the power lines), photographed at Mosgiel last Saturday, are quite rare. Photo by Ruth Thompson.
As a young girl, Ruth Thompson used to lie on the grass, stare at the sky and ''pick out the animals'' formed by the passing clouds.

Since then, she has remained a dedicated sky-watcher, and with her camera at the ready, she snaps any weird and wonderful formations that catch her eye.

Last Saturday afternoon, as she relaxed with a cup of tea in the conservatory of her Mosgiel home after a spell of gardening, she looked outside and thought ''now, that's different'', grabbed her camera and snap, we have today's photograph.

Like singer Joni Mitchell, who famously observed ''It's cloud's illusions I recall, I really don't know clouds at all'', Ruth had no idea what she had captured so asked The Wash if we could find someone who did know what the spiral-like clouds were.

We emailed her photo to Niwa meteorologist Chris Brandolino and here's what he had to say: ''Wow. A rare find! If I am not mistaken, this are Kelvin-Helmholtz Clouds.

They are rare, quite rare.

The `breaking waves' form as the result of shearing winds [changing wind speed and direction with height] at the cloud level.

A type of turbulence can develop in a layer of the cirrus cloud, which forms below an inversion [a region in the atmosphere where temperatures get warmer with height and not cooler as usually happens], thus this inversion creates a ceiling to stop the air/clouds from rising through it.

''Another way to envision is their formation is very similar to the formation of sea waves by the wind, or waves on the surface.

The wavy look is formed in the same way sea waves break where their crests are pushed ahead of their troughs [bottom] by the difference in current. In short, they are the atmospheric equivalent to breaking waves you see at the beach.

''They only last a minute or three once formed, so most don't see them - the photographer was lucky to see and capture the clouds!''Staying with Mosgiel, I can report a happy ending to yesterday's search for the owner of an old photograph found in Hagart-Alexander Dr last week by Jeanne Martin.

It belongs to Sandra Grant, who lives in that street. She mislaid it recently while sorting through some of her late husband Arthur's belongings.

Trevor Grant was one of several callers about the photograph, which showed the Grant family home ''Gladfield'' on the Mosgiel-Outram road.

Trevor says his father Douglas is in the picture and estimates he was between 1 and 2 years old, so the photo was probably taken around 1911.

Gladfield was pulled down in the mid-1980s but a previous owner, Glenda Taylor, says the barns in the background remain.

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