© Pekka Parviainen

Kustavi, Finland

Latitude: 60° 32' 42'' N

Longitude: 21° 21' 19'' E

10 August 1988 0043 (Local Time)

Image P/S code: P.10U.3.4

Image I.D.: 5795

• Images & related info Other Images Images of 1987 edition
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  Noctilucent cloud: type IVc

  The main type of noctilucent cloud in this picture is type IVc – whirls: a large-scale ring structure. In the upper left there are diffuse billows of type IIIb. In the upper right there is a complex structure of type O. There are also tropospheric clouds in the foreground.

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  © Pekka Parviainen
  Kustavi, Finland
  Latitude: 60° 32' 42'' N
  Longitude: 21° 21' 19'' E
  10 August 1988 0043 (Local Time)
  
  
  Image P/S code: P.10U.3.4
  Image I.D.: 5795
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  Noctilucent clouds

  Noctilucent clouds are seen here from an aircraft. These are high-altitude clouds that form near the mesopause during summertime and are visible to observers in mid to high latitudes when the Sun is below the horizon.

  There are bands or streaks with diffuse edges (type IIa) and there is one band with a sharply defined edge (type IIb). Short, straight and narrow billows (type IIIa) are also visible, as too are whirls with a small radius (type IVa), as seen at 4 and 5. Tropospheric clouds in the Earth's shadow appear as dark silhouettes against the background sky.

  Links in the image description will highlight features on the image. Mouse over the features for more detail.

  © Neil Gordon
  Québec J0M, Canada
  Latitude: 57° 9' 36'' N
  Longitude: 66° 1' 40'' W
  15 July 2015 0130 (Local Time)
  
  
  Camera direction: towards N
  Image P/S code: S.10
  Image I.D.: 5577
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  Noctilucent cloud

  Noctilucent clouds (NLC) are high-altitude, “night-shining” clouds that are generally only visible to observers in mid to high latitudes (approximately 50°N to 65°N or 50°S to 65°S) for a few months in summer. They occur higher than all other clouds, near the altitude of the mesopause, and are seen against the background of a dark sky when the Sun is well below the horizon, but while the clouds themselves are still illuminated by the Sun. 

  Several types of NLC appear in this picture. There is a very tenuous background veil (type I), which is faint and lacks any well-defined structure. There are also bands or streaks of cloud (type II), some of which have diffuse, blurred edges (type IIa) and some of which have sharply defined edges (type IIb). Short, straight and narrow billows (type IIIa) cross a band, which together is known as a complex structure of type P. One band is a curved whirl (type IV) and there is a bright area with a complex structure.  

  Tropospheric clouds in the Earth's shadow appear as dark silhouettes against the background sky. Noctilucent clouds, in contrast, appear brighter than the twilight sky as they are still illuminated at high altitude. A clear identifying feature of noctilucent clouds is their distinctive bluish-white colour.  

  Generally, noctilucent clouds will be seen close to the horizon. For this early morning view (in the northern hemisphere), the photographer is facing towards the north-east.

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  © Nicky Mack
  Lossiemouth, Scotland, United Kingdom of Great Britain and Northern Ireland
  Latitude: 57° 43' 12'' N
  Longitude: 3° 17' 52'' W
  18 October 2014 0315 (Local Time)
  
  
  Camera direction: towards NE
  Image P/S code: S.10
  Image I.D.: 5578
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  Noctilucent cloud

  This image shows several of the main types of noctilucent cloud: veil, bands, billows and whirls. The sky was clear with good visibility, but also with some low-level tropospheric cloud.

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  © Alan C. Tough
  Hopeman, Elgin, Scotland, United Kingdom of Great Britain and Northern Ireland
  Latitude: 57° 42' 38'' N
  Longitude: 3° 25' 38'' W
  09 June 2013 0023 (Local Time)
  
  
  Camera direction: towards NE
  Image P/S code: S.10
  Image I.D.: 5580
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  Noctilucent cloud

  This photograph shows a very bright display of noctilucent clouds. The clouds were sufficiently bright to illuminate ground features and cast faint shadows. It therefore rates as 5 on the 5-point brightness scale.

  The main types shown in the picture are type IIb – bands (streaks with sharply defined edges); type IIIa – billows (short, straight and narrow streaks); type IVa – whirls (whirls of small radius); type IVb – whirls (simple curves of 3° to 5°); and complex type O.

  Ground fog, also known as shallow fog, can be seen in the distance over the ground.

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  © Bill Ward
  Dalry, North Ayrshire, Scotland, United Kingdom of Great Britain and Northern Ireland
  Latitude: 55° 41' 7'' N
  Longitude: 4° 39' 8'' W
  03 July 2011 0115 (Local Time)
  
  
  Camera direction: towards N
  Image P/S code: S.10
  Image I.D.: 5692
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  Noctilucent cloud: type IVa

  Prominent in this picture is noctilucent cloud type IVa – whirls of small angular radius of curvature (0.1° to 0.5°). They may appear as small bright crests that look like ripples on water.

  Links in the image description will highlight features on the image. Mouse over the features for more detail.

  © Pekka Parviainen
  Turku, Finland
  Latitude: 60° 27' 6'' N
  Longitude: 22° 15' 60'' E
  28 July 1999 2335 (Local Time)
  
  
  Image P/S code: S.10
  Image I.D.: 5882