Coastal Gravity Currents: A Fog Formation Mechanism

Following the observations of the C-FOG field campaign that the interaction of a cold front and land mass under suitable conditions could lead to fog formation, laboratory and numerical studies were conducted to investigate flow hydrodynamics and turbulent mixing in a gravity current propagating over a rectangular obstacle. This is a simplified configuration of IOP 7 of the C-FOG campaign, and provided insights on mixing phenomena possible during coastal fog formation due to fronts. In the laboratory, the front was generated in a rectangular tank by lock exchange, and was allowed to interact with a solid rectangular block representing a peninsula. Time-resolved particle image velocimetry and planar laser-induced fluorescence were used for flow diagnostics, with phase alignment to remove inherent jitter of imaging. The experimental results were compared with well resolved large-eddy simulations performed using OpenFOAM. The model was validated by reproducing the time-dependent behavior of the gravity current propagation, and the numerical model was used for eliciting further details. The front-land interaction increased mixing and turbulent kinetic energy at and in the upstream of the obstacle at specific locations, generating locally enhanced mixing. These results, the measurements at C-FOG and their implications in fog formation will be discussed in this presentation.(funded by ONR grant # N00014-18-1-2472 entitled C-FOG: Toward Improving Coastal Fog Prediction)