Open AccessEntrainment in Shallow Rotating Gravity Currents: A Modeling Study
Author(s) -
Lars Umlauf,
Lars Arneborg,
Richard Hofmeister,
Hans Burchard
Publication year - 2010
Publication title -
journal of physical oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.706
H-Index - 143
eISSN - 1520-0485
pISSN - 0022-3670
DOI - 10.1175/2010jpo4367.1
Subject(s) - froude number , gravity current , entrainment (biomusicology) , mechanics , geology , transverse plane , secondary circulation , channelized , mixing (physics) , waves and shallow water , current (fluid) , physics , flow (mathematics) , internal wave , oceanography , telecommunications , structural engineering , quantum mechanics , rhythm , acoustics , computer science , engineering
The physics of shallow gravity currents passing through a rotating channel at subcritical Froude number is investigated here with a series of idealized numerical experiments. It is found that the combined effects of friction and rotation set up a complex transverse circulation that has some crucial implications for the entrainment process. A key component of this secondary circulation is a geostrophically balanced transverse jet in the interface that laterally drains fluid from the interface. This effect is shown to result in a strong cross-channel asymmetry and a spatial separation of the entrainment process: drained interfacial fluid is partly replaced by entrained ambient fluid on the deep side of the gravity current, whereas the downward mixing of buoyant fluid occurs on the shallow side. These results, closely corresponding to recent measurements in a shallow, channelized gravity current in the western Baltic Sea, illustrate that the description of entrainment as a strictly vertical mixing process with the help of local bulk parameters like the Froude number is not generally applicable in rotating gravity currents.