Between unperceived atmosphere, a subject for phenomenology, and perceived ambiance, a matter of exact science, the appearance of ambiance has rarely been explored, despite being essential to a better grasp of the modality of scansions, emerging from the sensorimotor flow, and the exact formation of an ambiance in the making. Here we present three modes of appearance: indexed appearance experienced as a form of discovery; surprising, astonishing epiphanic appearance; and pure appearance, suspended and indeterminate. But there is a fourth atmospheric situation, one of constantly disappearing appearance. This metabolic state leads straight to the crux of the aesthetic, ontological and ethical questions which conclude this paper.