Tuesday, 15 February 2011

Another elliptical halo

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Two posts and and three days back there was an elliptical halo in the sky and today ellipse appeared again. It had been a cold night with down to -30° C, and during the daytime as the thin cloud cleared and sun started shining more strongly, also crystal glitter in the air increased. Couple of times I looked out and saw only pillar and poorly defined subsun, but last check came also with faint elliptical halo. Above are different versions of the photos, stacked 13 frame average and lighten images and two single images. Heavily usmed average stack seems to indicate two slightly separate elliptical halos.

This formed in crystals precipitating from very low, almost invisible cloud layer. Temperature at Tampere stations ranged from -15 to -20° C at the time of the observation, the coldest being at Siilinkari on the lake Näsijärvi. I am not sure if heat plant plumes had anything to do with this. The connection was not obvious, at least.

Edit 15 February: Eetu Saarti saw much better ellipse in Kangasala the same day.

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