Over the last few days, an extraordinary event has unfolded in the skies over North Europe. The eruption of the Eyjafjallajokull volcano in Iceland has resulted in the formation of a massive ash cloud, which has had far-reaching effects on the atmosphere. This article delves into the unique atmospheric optics observed during this period and explores the fascinating details of this rare phenomenon.
One of the most striking observations during this period was the absence of contrails in the sky. Contrails, also known as vapor trails, are the visible trails of condensed water vapor left behind by aircraft engines at high altitudes. However, due to the volcanic ash present in the upper troposphere, all commercial air traffic was grounded in Holland and Great Britain. This resulted in a contrail-free sunset and a remarkably clear sky, allowing for a more pristine view of the celestial phenomena.
Contrary to some media reports, the sunsets and twilights during this period did not exhibit unusually vibrant colors. Instead, they appeared subdued, hazy, and slightly yellowish. This can be attributed to the presence of the ash particles in the troposphere, which scatter sunlight differently than the fine ash and sulfate aerosols typically found in higher regions of the atmosphere. As a result, sunsets and twilights took on a unique character, with a slightly more yellow-white twilight arch and a whitish glow near the horizon.
The ash particles emitted by the Eyjafjallajokull volcano are relatively large in size compared to those from more explosive eruptions. These larger particles are known as Mie scatterers, named after their scattering properties described by Gustav Mie. Unlike smaller Rayleigh scatterers, Mie scatterers cause light to scatter in different ways, leading to distinct optical effects. This distinction is crucial in understanding the specific atmospheric optics observed during this period.
Another captivating phenomenon witnessed during this time was the appearance of Bishop's Rings. These rings are essentially the aureole, or halo, of a large corona produced by the diffraction of light by small particles. The ash particles in the atmosphere served as the perfect medium for creating these mesmerizing rings. By diffracting sunlight, they produced an ethereal display that added to the already awe-inspiring spectacle in the sky.
The impact of the volcanic ash was not limited to sunsets alone. Observers also noted significant changes during sunrise. The morning sky exhibited a pale appearance, reminiscent of the effect caused by African dust reaching the region in late spring. The relative humidity was relatively high, ruling out the possibility of vapor or mist as the cause. This sunrise, devoid of any aircraft presence, presented a surreal experience with its quietude and the enchanting songs of nearby nightingales.
The combination of contrail-free skies, subdued sunsets and twilights, Bishop's Rings, and unique sunrises made the Eyjafjallajokull eruption an extraordinary event for atmospheric optics enthusiasts. These observations provided a rare opportunity to witness the interplay between natural phenomena and human activities in shaping our atmosphere. While volcanic eruptions can disrupt air travel and cause inconvenience, they also offer us a chance to appreciate the beauty and complexity of our planet's atmospheric dynamics.
In conclusion, the Eyjafjallajokull eruption created a spectacle in the skies that captivated observers across North Europe. From the absence of contrails to the subdued sunsets and twilights, each aspect of this event revealed a unique facet of atmospheric optics. The presence of Mie scatterers and the formation of Bishop's Rings added further intrigue to the already mesmerizing display. It serves as a reminder of the intricate interplay between natural phenomena and the atmosphere, showcasing the captivating wonders that can unfold above our heads.
Eyjafjallajokull Skies ~ Over the last few days (April 17 - later developments 1, 2) an ash cloud from the Icelandic volcano has carried over North Europe.
The top image was taken by Hans Nienhuis in The Netherlands on the evening of April 16. It is remarkable for what is does not show as well as its subtle sun pillar. �The sunset was not really reddish. There was just a faint sun pillar, like those seen so many other times. But more interesting is the clean sky around it - no contrails at all. Due to the volcanic ash in the upper troposphere all the commercial air traffic was shut down in Holland, like that in Great Britain also.
I'm not really old, but I have never seen this in my whole life, and probably will never see it again. A contrail free sunset and thus a faint sun pillar, not caused or disturbed by any anthropogenic aircraft activities. Despite it's "usual" appearance a unique view!� Aircraft over a large part of Europe were grounded.
The ash is in a number of thin layers in the troposphere and of fairly large particle size. Some is already falling out. This contrasts with the very fine ash and sulfate aerosol of larger and more explosive eruptions that circulates the planet higher in the stratosphere. The Icelandic larger particles are Mie rather than Rayleigh scatterers.
Thus � and notwithstanding lurid sunset images appearing in the media � there have not been colourful sunsets or twilights outside the normal range of their appearance. Instead, sunsets have so far been subdued, hazy and perhaps slightly yellowish. Twilights have had a slightly more yellow-white twilight arch with a whitish glow near the horizon later on.
The second image shows a Bishop�s Ring over Deventer, Holland on the morning of April 16 and imaged by Peter Paul Hattinga Verschure. These rings are essentially the aureole of a huge corona produced by diffraction by small particles.
The two lower images show Saturday�s (17th) dawn in Hungary pictured by Monika Landy-Gyebnar. �I was out to look at the sunrise. It was really pale. The effect was very similar to that of African dust when sometimes it reaches our region in late spring, Mr. Mie was doing a great job! Even the shadows had no contrast on the ground. The relative humidity was about 75%, so it could not be vapour or mist.
But besides being pale this was a really impressive sunrise. There were no planes up in the sky! No contrails, no glints of light on the aircraft, no noise, only the stunning beautiful song of some nightingales nearby.�
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"Eyjafjallajokull Skies". Atmospheric Optics. Accessed on December 10, 2023. https://atoptics.co.uk/blog/eyjafjallajokull-skies/.
"Eyjafjallajokull Skies". Atmospheric Optics, https://atoptics.co.uk/blog/eyjafjallajokull-skies/. Accessed 10 December, 2023
Eyjafjallajokull Skies. Atmospheric Optics. Retrieved from https://atoptics.co.uk/blog/eyjafjallajokull-skies/.