© Kevin Boyle
Stoke-on-Trent, England, United Kingdom of Great Britain and Northern Ireland
Latitude: 53° 6' 0'' N
Longitude: 2° 12' 0'' W
19 February 2008 1749 (Local Time)
Image P/S code: P.10U.2
Image I.D.: 6046
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Polar stratospheric cloud: nitric acid and water
Polar stratospheric clouds occur only in high-latitude regions during the winter, or near winter, when temperatures in the lower and middle stratosphere fall below about –78 °C for nitric acid trihydrate clouds, –81 °C for supercooled ternary solution polar stratospheric clouds and –85 °C for ice polar stratospheric clouds (nacreous or mother-of-pearl clouds).
Nitric acid trihydrate and supercooled ternary solution polar stratospheric clouds may appear as a thin, yellowish veil, as in this picture taken during a rare occurrence over England. These types of polar stratospheric clouds do not display the bright iridescent colours of the nacreous, mother-of-pearl type of polar stratospheric cloud. Indeed, due to their diffuse appearance, nitric acid and water polar stratospheric clouds may be confused with either Cirrostratus cloud or a layer of haze.
Polar stratospheric clouds are best viewed after sunset (as in this picture) or before sunrise, during the period of civil twilight when the Sun is between about 1° and 6° below the horizon. The clouds in silhouette near the horizon are tropospheric clouds.
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© Kevin BoyleStoke-on-Trent, England, United Kingdom of Great Britain and Northern IrelandLatitude: 53° 6' 0'' NLongitude: 2° 12' 0'' W19 February 2008 1749 (Local Time)Image P/S code: P.10U.2Image I.D.: 6046
Purple light
Twilight colours are produced by the refraction, scattering or selective absorption of light rays from the Sun in the atmosphere. They can be observed in clear, cloudless air after sunset or before sunrise.
In the direction of the Sun during twilight, a glow called the purple light is sometimes seen. This appears as a segment of a large luminous disk and extends upwards from the horizon, reaching maximum luminance when the Sun is 3° or 4° below the horizon. It then descends and disappears when the Sun is about 6° below the horizon.
On very rare occasions, the top of the twilight arch may become a very noticeable vivid purple colour, more intense than any purple tinge normally seen at twilight. Such extremely visually striking instances of the purple light seem to be associated with either fine volcanic dust in the atmosphere or the occurrence of polar stratospheric clouds.
Between 17 and 20 February 2008, there were widespread observations in central and western Europe of extraordinary, intense purple twilights. This event has been linked to very low stratospheric temperatures and the formation of polar stratospheric clouds (although no polar stratospheric clouds were actually seen by the observer). The photograph here was taken in evening twilight on the 18th from a location in southern England, UK. The true vividness of the colours is difficult to capture in a photograph, but above the bright twilight arch at the top of the photograph there is a distinct purple colour to the sky.
Links in the image description will highlight features on the image. Mouse over the features for more detail.
© Stephen BurtStratfield Mortimer, near Reading, England, United Kingdom of Great Britain and Northern IrelandLatitude: 51° 22' 12'' NLongitude: 1° 2' 24'' W18 February 2008 1750 (Local Time)Camera direction: towards WSWImage P/S code: P.13.11.1Image I.D.: 5676
Purple light
Twilight colours are produced by the refraction, scattering or selective absorption of light rays from the Sun in the atmosphere. They can be observed in clear, cloudless air after sunset or before sunrise.
In the direction of the Sun during twilight, a glow called the purple light is sometimes seen. This appears as a segment of a large luminous disk and extends upwards from the horizon, reaching maximum luminance when the Sun is 3° or 4° below the horizon. It then descends and disappears when the Sun is about 6° below the horizon.
On very rare occasions, the top of the twilight arch may become a very noticeable vivid purple colour, more intense than any purple tinge normally seen at twilight. Such extremely visually striking instances of the purple light seem to be associated with either fine volcanic dust in the atmosphere or the occurrence of polar stratospheric clouds.
Between 17 and 20 February 2008, there were widespread observations in central and western Europe of extraordinary, intense purple twilights. This event has been linked to very low stratospheric temperatures and the formation of polar stratospheric clouds.
This photograph was taken in evening twilight from a location in southern England, UK. It is difficult to record the true vivid nature of the purple glow in a photograph, but a distinct purple colouration can be seen across the sky in the image. The polar stratospheric clouds likely responsible were not seen by the observer.
Links in the image description will highlight features on the image. Mouse over the features for more detail.
© Stephen BurtStratfield Mortimer, near Reading, England, United Kingdom of Great Britain and Northern IrelandLatitude: 51° 22' 12'' NLongitude: 1° 2' 24'' W19 February 2008 1748 (Local Time)Camera direction: towards WSWImage P/S code: S.13.11.1Image I.D.: 5677
Purple light
Twilight colours are produced by the refraction, scattering or selective absorption of light rays from the Sun in the atmosphere. They can be observed in clear, cloudless air after sunset or before sunrise.
In the direction of the Sun during twilight, a glow called the purple light is sometimes seen. This appears as a segment of a large luminous disk and extends upwards from the horizon, reaching maximum luminance when the Sun is 3° or 4° below the horizon. It descends and disappears when the Sun is about 6° below the horizon.
On very rare occasions, the top of the twilight arch may become a very noticeable vivid purple colour, more intense than any purple tinge normally seen at twilight. Such extremely visually striking instances of the purple light seem to be associated with either fine volcanic dust in the atmosphere or the occurrence of polar stratospheric clouds.
Between 17 and 20 February 2008, there were widespread observations in central and western Europe of extraordinary, intense purple twilights. This event has been linked to very low stratospheric temperatures and the formation of polar stratospheric clouds. This photograph of the purple light was taken in the evening on the 17th from a location in England, UK. The true vividness of the colours are difficult to capture in a photograph, but above the bright twilight arch there is a distinct purple colour to the sky.
Links in the image description will highlight features on the image. Mouse over the features for more detail.
© Kevin BoyleStoke-on-Trent, United Kingdom of Great Britain and Northern IrelandLatitude: 53° 6' 0'' NLongitude: 2° 12' 0'' W17 February 2008 1750 (Local Time)Camera direction: towards WSWImage P/S code: S.13.11.1Image I.D.: 5998