© Mark Zalcik

Namao, Alberta, Canada

Latitude: 53° 43' 2'' N

Longitude: 113° 29' 39'' W

26 June 2014 2343 (Local Time)
Camera direction: towards NW

Image P/S code: P.10U.3.5

Image I.D.: 5687

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  Noctilucent cloud: complex structure

  Often in displays of noctilucent cloud, several forms may be seen simultaneously. It is not unusual, therefore, for two or more intersecting or overlapping groups to give rise to complex structures such as bright knots or net-like structures, or types that do not fit the standard classifications. This picture, taken just before midnight from the Edmonton area of Alberta, Canada, shows one such complex display of noctilucent cloud. The central part of the display had a peculiar billow-like appearance with a number of lacunosus holes.

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

  © Mark Zalcik
  Namao, Alberta, Canada
  Latitude: 53° 43' 2'' N
  Longitude: 113° 29' 39'' W
  26 June 2014 2343 (Local Time)
  
  
  Camera direction: towards NW
  Image P/S code: P.10U.3.5
  Image I.D.: 5687
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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.

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

  © 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: complex structure

  Often in displays of noctilucent cloud, several forms may be seen simultaneously. It is not unusual, therefore, for two or more intersecting or overlapping groups to give rise to complex structures (for example, bright knots or net-like structures) or types that do not fit the standard classifications.

  This picture, taken during evening twilight just east of the city of the Edmonton in Alberta, Canada, shows one such complex display of noctilucent cloud. The display was the brightest the observer had seen in 35 years of observing noctilucent cloud and clearly rated as 5 on the 5-point brightness scale. In general, it may be classed as type O, but there is the suggestion of a large-scale ring structure (type IVc) that is essentially a large oval of noctilucent cloud visible in the upper left part of the image.

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

  © Mark Zalcik
  Clover Bar area, Edmonton, Alberta, Canada
  Latitude: 53° 34' 40'' N
  Longitude: 113° 20' 37'' W
  03 July 2005 0000 (Local Time)
  
  
  Camera direction: towards NW
  Image P/S code: S.10
  Image I.D.: 5582
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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.

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

  © 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: complex type O

  This photograph shows a form of noctilucent cloud that does not fit into types I to IV. This is complex type O.

  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
  16 July 1978 2125 (Local Time)
  
  
  Image P/S code: S.10
  Image I.D.: 5794
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  Noctilucent cloud: type P

  In some displays of noctilucent cloud, two or more forms may be seen simultaneously, and it is not unusual for two types to intersect. In this picture, billows cross bands to form the complex structure of type P.  

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

  © Pekka Parviainen
  Kustavi, Finland
  Latitude: 60° 32' 42'' N
  Longitude: 21° 21' 19'' E
  26 July 1989 2312 (Local Time)
  
  
  Image P/S code: S.10
  Image I.D.: 5880
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  Noctilucent cloud: type S

  In some displays of noctilucent cloud, two or more forms may be seen simultaneously, and it is not unusual for types to intersect with each other. In this picture, bands cross billows to form bright knots (type S) at 3 and 4.

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

  © Pekka Parviainen
  Kustavi, Finland
  Latitude: 60° 32' 42'' N
  Longitude: 21° 21' 19'' E
  12 July 2005 2154 (Local Time)
  
  
  Image P/S code: S.10
  Image I.D.: 5881