Cloud obsession?

6 May 2019

Because I'm both a birder (who likes to take photos) and an astrophotographer, I'm always keeping an eye on the clouds.

The other day I was walking the dog in the local park. It was humid and threatening to rain, and the clouds were fairly dramatic, as the picture shows. There was a thin band of dark, mid-level cloud starting to form ahead of a rain band, but above that was a large gap, with much higher cloud behind it.

But there was a stripe across the sky, which was dark in the middle with light edges. What was it, and what caused it?

It was an aeroplane approaching Tullamarine. It had been flying in the clear area between the two cloud layers and was just descending into the thin lower layer. My guess is that the plane's wings were pushing the air immediately below it downwards into the clear air below, while vortices at the end of the plane's wings were pushing the air there upwards into the layer above.

The band of cloud must have been pretty thin for the plane to be able to knock it around like that.

Can anyone confirm this?

As I watched, a second plane came through, and it tore the clouds up in the same way. But five minutes later, it wasn't happening any more.

I suppose that for the time when it was happening the conditions for cloud formation must have been just on the very edge, or the cloud would have just reformed after the plane passed. It certainly made from a pretty dramatic sky canvas.

For astrophotography, I refer to Cloud Free Night, which provides me with predictions for a number of places that are good for sky watching, specifically Heathcote, of course. Have a play with it. You might find it useful.

Apart from the Bureau of Meteorology, I don't get as specific with bird watching. The lens I use for birding is fairly slow, which means if the sun isn't shining, it's best to leave it at home and enjoy the birds through binoculars.