1. An organized unit of convection within a convecting layer. It is isolated by a stream surface, with ascending motion in the center and descending motion near the periphery, or vice versa. In laboratory convection, such cells (sometimes referred to as Bénard cells) are usually roughly as deep as they are wide, may take the form of squares, triangles, or hexagons, and may be laminar or turbulent and steady or oscillatory. In atmospheric boundary layer convection, this term refers to an organization of turbulent convection on horizontal scales at least as large as the depth of the convective boundary layer. In the case of cloud-topped boundary layers, convection cells may take the form of open cells, with broad, cloud-free areas of gentle descent surrounded by narrow updrafts within cumulus clouds, or may take the form of closed cells in stratocumulus clouds, characterized by narrow downdrafts at the periphery. See also cell, airmass thunderstorm, ordinary cell. 2. In the case of precipitating moist convection, refers to a distinct unit of convection, often having its own closed contours of radar reflectivity and a lifetime of roughly 20–30 minutes. Such a cell generally begins as a cumulus updraft, then develops a precipitation-driven downdraft, and finally decays as a general, cloudy area containing weak downdrafts.