International Cloud Atlas Volume I Revised edition 1975
http://library.wmo.int/pmb_ged/wmo_407_en-v1.pdf
International Cloud Atlas Volume II 1987
http://library.wmo.int/pmb_ged/wmo_407_en-v2.pdf
International Cloud Atlas 2017 (site search)
https://www.wmocloudatlas.org/search-image-gallery.html
