Structure and dynamics of the near-surface water layer under conditions of natural convection.

This article focuses on laboratory and numerical investigations of the submergence dynamics of density fronts formed by ensembles of jets—thermal-like structures with negative buoyancy—during surface water cooling. The study identifies three distinct stages in the deepening process, characterized by nonlinear velocity changes and vortex formation, with measured deepening velocities around 0.15 cm/s, indicating laminar convective flow (Reynolds numbers between 3 and 60). A geometric model was developed to describe the shape and scale of thermals and jets, revealing differences in volume, shape, and velocity between individual thermals and jets within ensembles. The findings suggest that turbulence observed in seawater measurements is externally induced rather than generated by free convection during surface cooling, highlighting the dominance of thermal or saline turbulence over free convection in ocean heat exchange processes.