Extremely high cirriform List of cloud types

noctilucent cloud on estonia

noctilucent clouds thin, cirriform-looking clouds, based 80 to 85 kilometres (262,000–279,000 ft) , seen in deep twilight after sunset , before sunrise.

type 1 
very tenuous; resembles cirrus.
type 2 
bands. long streaks, in parallel groups or interwoven @ small angles.

subtypes


2a 
streaks diffuse, blurred edges.
2b 
streaks sharply defined edges.






type 3
billows. spaced, parallel short streaks.

subtypes


3a 
short, straight, narrow streaks.
3b 
wave-like structures undulations.






type 4 
whirls. partial (or, more rarely, complete) rings dark centers.

subtypes


4a 
whirls possessing small angular radius of curvature, resembling light ripples on water surface.
4b 
simple curve of medium angular radius 1 or more bands.
4c 
whirls large-scale ring structures.








^ world meteorological organization, ed. (1975). noctilucent, international cloud atlas (pdf). i. p. 66. isbn 92-63-10407-7. retrieved 26 august 2014. 
^ michael gadsden & pekka parviainen (september 2006). observing noctilucent clouds (pdf). international association of geomagnetism & aeronomy. p. 9. retrieved 31 january 2011.