Fog-laden density staircases in the marine atmospheric boundary layer

The formation of a layered structure in the form vertically separated density steps (staircases) stably stratified fluids has been reported many laboratory and oceanic studies as well terrestrial atmospheric boundary layer (ABL) to lesser extent, with attribution different dynamical mechanisms. This paper presents observations structures fog-laden marine ABL, where both fog appear almost simultaneously following turbulent mixing event under nocturnal conditions. were made during C-FOG (2018) field campaign aboard research vessel using rawinsonde launches, aided by suite supporting onboard instruments. is case great practical interest because impediment staircases optical near-infrared wave propagation ABL due enhanced beam jitter attenuation fog. A new mechanism proposed explain genesis layering, wherein when fluid parcels significant buoyancy differences ( $$\Delta b$$ ) osculate regions weak turbulence (local length velocity scales, $${L}_{H}$$ $${u}_{H}$$ , respectively) devoid adequate inertial forces $$\sim {u}_{H}^{2}/{L}_{H}$$ cause stir past each other. expressed terms local bulk Richardson number criterion $$Ri= {\Delta b{L}_{H}/{u}_{H}^{2}>Ri}_{c}$$ $${Ri}_{c}$$ critical value. simple experiment an idealized (three layer) stratification known source (oscillating grid) was performed demonstrate mechanism, through combination measurements modeling it found $$\approx$$ 1.5. consistent representative previous layering atmosphere ocean localized events caused Kelvin–Helmholtz billowing.