“Unkai” (「雲海」, literally “sea of clouds”) is a phenomenon which occurs when a cold upper atmosphere inputting downward pressure meets a damp, warmer lower atmosphere which wants to rise in a basin, causing immense condensation. The Aso caldera is quite famous for this. Our friend Yoshiko Toyama captured this gorgeous photo of the phenomenon. I don’t know how to advise our photographer readers on timing to capture this, but perhaps you should consult an elderly photographer - they seem to know when it will appear (not saying that Yoshiko-san is elderly, mind). - William