Sunday 18 April 2010

Aircraft-less skies, but is the volcanic dust really visible?

Following the eruption of the Eyjafjallajoekull volcano of Iceland and the large amounts of dust it ejected into the atmosphere, airtraffic over NW Europe, including my country, has been completely halted. For four days now, this has resulted in unique airplane-less and contrail-less skies.

The sky is somewhat hazy for days here now, but is this due to the volcanic dust? Is it visible at all (as it was here after the 1991 Pinatubo eruption, causing pinkish-purple dusk skies)? Dutch news reports on Friday carried many photographs of red evening skies and red streaky clouds, purported to be the "volcanic dust". But all showed what to me looked like normal "evening red", sun-reddened cirrus clouds, and some even showed normal cumulonimbus!

I (and several Dutch astronomy and weather amateurs with me) have watched the evening skies the past days for anything unusual that could be attributed to the dust. But we failed to see anything more than what could very well be normal "evening red". Quite disappointing!

Below image was shot by me on Friday evening 16 April 2010 at about 18:29 UTC (20:29 CEST), some 10 minutes before sunset. Visible is a faint halo in the haze.

click image to enlarge

The orange is, in my opinion, normal evening red. And the halo: is it a "normal" halo in cirrus, or is it the "Ring of Bishop", due to dust?

The answer comes from a closer look. I have taken a part of the halo image, and increased the colour saturation to show the colour better. What can be seen (image below), is that the red/orange part of the spectrum is located at the inner side of the ring.

This means the ring is a halo in ice particles: in a dust-induced Bishop's ring, the red should be on the outside.

click image to enlarge

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