The Aso caldera is one of the world’s largest - and deepest. It thus traps cold, denser air. When warmer, wet air flies above, a phenomenon known as “sea of clouds” (unkai, 雲海) generates due to temperature inversion. Kumanichi reports that this year’s first occurred in the morning of the 14th, when the temperature of the caldera basin was -2.6°C and a warm, wet band was passing overhead.
For our photographer friends who want to capture this, choose a cold day with a southern-coming rain front approaching. - William
