Relative buoyancy dominates thermal-like flow interaction along an incline

This paper describes laboratory investigations of the motion between two fixed volumes of dense fluid (surge-type gravity currents) with different salt concentrations that interact above an incline in the presence of ambient stratification. The experiments include both large and small density contrasts between the interacting surges. Initially, the propagation of each fluid mass assumes a thermal-like nature. but then the lower density surge is quickly caught up by the denser fluid flow because of its higher velocity. There are two key process regarding the surge interaction. With a large density contrasting the fluid volumes, the denser flow moves to the front of the current as an intrusion with no mixing. With a small density difference, pronounced mixing occurs between the surges with the development of a homogeneous underflow. A simple energy parameterization is developed to evaluate the source conditions under which the different flow dynamics develop.