Sunday, May 14, 2006

Small and large coronas

How small is a pollen corona! On 14 May, a fine circular pollen corona re-appeared in clear sky blue over Deventer. It was magnified by zooming the camera lens, but actually real proportions of this small phenomenon are disguised by doing so. Here we see a fraction of a common water droplet corona in Fractocumulus too, left in the image. It is nice to see the differences in corona proportions, by considering pollencoronas, via common cloud coronas, to Bishops' ring....

4 comments:

Les Cowley said...

Peter-Paul, the 'average diameter' of the pollen sampled and shown in your earlier posting is about 70 micron. This will give a first red ring radius of around 0.9° compared with several degrees for a water droplet corona. As your nice image already shows!

Marko Riikonen said...

Bishop's ring, which is about the size of 22° halo is not the largest corona. During the last two weeks we have had here reports of a corona of the size of 46° halo. In Chile I photographed such corona.

Peter-Paul Hattinga Verschure said...

That's great in double sense, Marko. What kind of corona is this large type ? By what is it caused ?

Marko Riikonen said...

The one that showed here about two weeks ago may have been caused by the fires in Estonia and other countries down south. The sky was hazy and weather service guys told it's because of those fires.

In Chile I was in Atacama Andes and there is no really chances for major vegetation burns. It may be related to mines, they spread huge dust clouds around the area. This was the most colorful I've seen, with blue inside and green and red on the border. Altocumulus was forming from the stuff that made the corona.

You must observe these coronas with convex mirros, othervise you may not notice them at all. Of cource, the colors are greatly diluted in photos.

We see these big coronas every summer in Finland. Jari Piikki noted that they usually occur in the end of hot weather periods. Are they all related to vegetation burns, I don't know.