Laboratory and Numerical Study of the Peculiarities of Sea Surface Cooling in Coastal Waters

The initial phases of penetration of cold waters from the sea surface into the depth are analyzed within a study of the process of sea surface cooling. The phases of immersion of small volumes of water with negative buoyancy, reaching the bottom, and propagation along the bottom slope have been studied in laboratory experiment and numerical simulation. The interaction between two small volumes of salt water, which sequentially originate in the surface freshwater layer, during their immersion and subsequent propagation along the bottom slope is described in detail. Laboratory experiments have shown that the second of two water spots, equal in volumes and negative buoyancy, always reaches the first one during propagation along the bottom slope. A phenomenological explanation of this fact is suggested. The images of individual phases of the water-spot propagation show quite long-term stability of laminar structure of tracers inside the water spots. The simulation allows distinguishing two characteristic phases (advective and viscous) of interaction between two water spots. The experimental and simulation results allow us to suggest the general scheme of the negative-buoyancy water dynamics in coastal waters.