by Penny Holliday
Late this afternoon we completed our most northern CTD station, just a short distance from the islands around Vestmannaeyjar off the southern coast of Iceland. We have spent the whole day steaming here after we broke off our CTD section at 61°N because of worsening weather. The forecast suggested that the northern part of our section would have better weather, so in order not to waste time being hove to in unworkable conditions, we took the decision to head north. It has worked out well because the winds are light here and conditions perfect for CTDs.
The views of land have not been quite up to the standard we became accustomed to around Greenland. The mainland of Iceland is a long way from here and remained hidden behind the low cloud and patchy fog drifting around us. The volcanic islands that we did see were rather shy and only peeked briefly out from the mist and cloud. But in contrast, the sea and sky gave us ever changing and really quite beautiful views – I’ve posted some photographs below.
We were all rather surprised to see a strange flattened rainbow on the edge of one of the fog patches – see the photograph below. If anyone can tell us what this phenomenum is called and how it forms we would be very interested to know. Please leave a comment here or send me an email (nph).
From here we are going do a few more CTD stations as we head back south along 20°W until we get to the place that we broke off the section. After doing a CTD we will commence the search for Bellatrix the glider that is waiting for us there. Gliders are small robotic devices not much bigger than the Argo floats I wrote about yesterday. However unlike floats that drift with the currents, gliders can be “driven” to particular places. Bellatrix (named after the star) has been patrolling the Extended Ellett Line for some time and we will pick her up so she can be serviced and have new batteries before her next mission. I will write more about gliders when we have recovered Bellatrix and have some photos to show you.
Images: the flat rainbow, two views of stunning clouds and light, one of the shy islands, and a reassuringly curved rainbow (all by Penny Holliday)
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- 140711 flat rainbow
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- 140711 lovely sky 1
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- 140711 lovely sky 2
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- 140711 island
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- 140711 reassuringly curved rainbow
UK OSNAP at sea 
Hi Penny, the horizontal rainbow you saw is called ‘fire rainbow’ or ‘circumhorizontal arc’: “The complete halo is a huge, multi-coloured band running parallel to the horizon with its centre beneath the sun. ” (from wikipedia http://en.wikipedia.org/wiki/Circumhorizontal_arc).
Safe travels! Marjan
I think no “fire rainbow” that I know of. But I am wondering if Marjanslaats has seen the same as your photo, and at similar latitude, and/or in similar conditions.
Is the following correct? Your mystery arc has red on the convex side. It is convex-upwards. You were seeing it in low mist at temperatures well above 0 degrees C. (I believe a “fire rainbow” is red on the concave side, is concave-upwards, and is an effect of ice crystals at high altitude.)
Am I right in thinking that your back is towards the sun, like normal rainbows including any double rainbow? (All other halos I have seen, or can find reference to, are seen when looking towards the sun.)
In general, spherical water droplets, being radially symmetrical about the incoming ray, refract light into cones of ray paths (“rainbows”). Ice, being crystalline, is capable of refracting light to a single linear direction (e.g. “sundogs”), though it may also spread into cones (“halos” and other arcs). Your “flat rainbow” looks to me like a normal rainbow, caused in water droplets that are parallel-illuminated from a direction far too near vertical to be direct from the sun. The trouble with that hypothesis is that you haven’t blogged about a strange second “sun” very high in the sky.
To get any further, it would be interesting to know the angular width of the rainbow (compared to normal, if not in numbers), the direction of viewing compared to the sun, time of day, latitude, and more about the weather conditions.
Perhaps you and Marjanslaats are onto something!
Hm! Vastly more likely to be a “rainbow”, in bowspray blowing over the ship and drifting away just above deck height through the beam of a downward pointing spotlight. Second thoughts are always less exciting.
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