Motion in Stratified Fluids

Density stratification due to temperature or salinity variations greatly influences the flow around and the sedimentation of objects such as particles, drops, bubbles, and small organisms in the atmosphere, oceans, and lakes. Density stratification hampers the vertical flow and substantially affects the sedimentation of an isolated object, the hydrodynamic interactions between a pair of objects, and the collective behavior of suspensions in various ways, depending on the relative magnitude of stratification, inertia (advection), and viscous (diffusion) effects. This review discusses these effects and their hydrodynamic mechanisms in some commonly observed fluid-particle transport phenomena in oceans and the atmosphere. Physical understanding of these mechanisms can help us better model these phenomena and, hence, predict their geophysical, engineering, ecological, and environmental implications.