circumhorizon arc

少し古いnewsになりましたが，一昨日，各地で観測されたrainbow-like phenomenonの記事です。circumhorizon arc という言い回しにロマンを感じてしまいました。これはどのような意味でしょうか。Inahoさん，どうぞ。（Starlight）

A rare rainbow-like phenomenon among thin clouds in the sky was seen over part of Japan.

The Meteorological Agency says the circumhorizon arc was visible at about 10:30 AM on Friday over Shizuoka Prefecture, central Japan, and some other areas.

The agency says it is created when refracted rays of the sun radiate out in the colors of the rainbow in thin clouds that are made up of ice grains.

The agency adds it can be observed only a few times a year, mainly in summer when the sun is high in the sky.

http://newsonjapan.com/html/newsdesk/article/112624.php#sthash.brgHwS8T.dpuf