© 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.10U.3.5
Image I.D.: 5881

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.
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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.
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