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Nacreous Clouds!!


Peter Hill


We are normally cursing the clouds, but for once they put on a very dramatic display this evening between 18:00 and 18:20.
Was sitting chatting in the lounge when I saw cloud1r, or something a bit more brighter and colourful, immediately thought of nacreous clouds, several examples of which have featured lately on
There is currently an example on at the present, taken in Norway, nacreous clouds are stratospheric phenomena and as can be seen form the shots I've posted these are not stratospheric, so no, not nacreous or " mother of pearl" clouds ,but  the poor relation, iridescent clouds as described in this extract from
Atmospheric optics
When parts of clouds are thin and have similar size droplets, diffraction can make them shine with colours like a corona. In fact, the colours are essentially corona fragments. The effect is called cloud iridescence or irisation, terms derived from Iris the Greek personification of the rainbow.

The usually delicate colours can be in almost random patches or bands at cloud edges. They are only organised into coronal rings when the droplet size is uniform right across the cloud. The bands and colours change or come and go as the cloud evolves. They occur most often in altocumulus, cirrocumulus and especially in
lenticular clouds. Iridescence is seen mostly when part of a cloud is forming because then all the droplets have a similar history and consequently have a similar size.

Sometimes iridescence can be seen far from the sun but is most frequent near to it. As for coronas, search safely by hiding the sun behind a building and, even better, also viewing the reflection of the sky in water.

Very much rarer iridescence is that of
nacreous or mother-of-pearl clouds. They can glow very brightly and are far higher than ordinary tropospheric clouds. Iridescence is also seen in rocket exhaust trails

Some of the clouds were definitely lenticular and  they gave a pretty spectacular display and the whole scene was very dynamic for some 20 mins.
Shots taken on Canon 450D , handheld, F10, Tamron 18-270mm lens, focus at infinity using manual focus, ISO400, exp 1/50",typical values, obviously changed focus for cloud3r, with uniform sky, not enough difference to auto-focus, being hand held image stabilisation on. Taken in RAW and tweaked in P.S.
Pete H

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