Wind-Driven Overturning, Mixing and Upwelling in Shallow Water: A Nonhydrostatic Modeling Study

Using a nonhydrostatic numerical model, this work demonstrates that onshore winds are a principal agent of overturning and vigorous vertical mixing in nearshore water of lakes and inner continental shelves. On short (superinertial) timescales of a few hours, onshore winds create surface currents pus...

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Bibliographic Details
Published in:Journal of marine science and engineering 2017-12, Vol.5 (4), p.47
Main Author: Kämpf, Jochen
Format: Article
Language:English
Subjects:
Biogeochemical cycle
Biogeochemical cycles
Biogeochemistry
Continental shelves
Density stratification
Dynamic stability
Gravitational waves
Gravity
Gravity waves
Instability
Internal waves
Kelvin-helmholtz instability
Lakes
limnology
Mathematical models
Modelling
Nearshore water
nonhydrostatic modelling
Ocean circulation
oceanography
overturning
Pressure gradients
Shallow water
Shelf seas
Stratification
Surface currents
Tidal mixing
Undercurrents
Upwelling
Vertical mixing
Water column
Water currents
Wave reflection
Wind
Winds
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Summary:Using a nonhydrostatic numerical model, this work demonstrates that onshore winds are a principal agent of overturning and vigorous vertical mixing in nearshore water of lakes and inner continental shelves. On short (superinertial) timescales of a few hours, onshore winds create surface currents pushing water against the shore which, via the associated pressure gradient force, creates an undercurrent. The resulting overturning circulation rapidly becomes dynamically unstable due to the Kelvin-Helmholtz instability mechanism, internal gravity waves form, and vigorous vertical mixing follows. The vertical extent of the overturning cell depends on the speed of surface currents and density stratification (which is influenced by other processes such as tidal mixing). In smaller enclosed water bodies, wave reflection in conjunction with dynamical instabilities support rapid mixed-layer deepening and overturning of the entire water column. Based on these findings, the author postulates that dynamic instabilities following from onshore wind events are of fundamental importance to biogeochemical cycles and ecological processes in shelf seas and lakes.
ISSN:2077-1312
2077-1312
DOI:10.3390/jmse5040047