According to the “Morris Dictionary of Word and Phrase Origins,” the phrase is based on U.S. Weather Service terminology. This theory holds that cloud types are numbered, and that “cloud nine” is the designation given to “cumulonimbus” clouds, the highest-flying clouds around, making them an apt metaphor for being “on top of the world.” When “you’re on cloud nine” you feel wonderful ! Like nothing else is really very important. (Reference: wiki.answers)
At 30,000 feet, i am really on cloud 9.
The plane just landed in Manila. The feeling of excitement, extreme joy, to be back home again and be with my loved ones, this is my true definition of being on CLOUD 9.
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my sweetpainteddreams 
I saw a similar view today on my way to Texas. The clouds were beautiful like in your photos. Indeed it was cloud 9… Thanks!