Belcher, S. E., Grant, A. L.M., Hanley, K. E., Fox-Kemper, B., Van Roekel, L., Sullivan, P. P., Large, W. G., Brown, A., Hines, A., Calvert, D., Rutgersson, A., Pettersson, H., Bidlot, J.-R., Janssen, P. A.E.M. and Polton, J. A.
A global perspective on Langmuir turbulence in the ocean surface boundary layer.
Geophysical Research Letters, 39 (L18605).
The turbulent mixing in thin ocean surface boundary
layers (OSBL), which occupy the upper 100 m or so of the
ocean, control the exchange of heat and trace gases between
the atmosphere and ocean. Here we show that current parameterizations
of this turbulent mixing lead to systematic and
substantial errors in the depth of the OSBL in global climate
models, which then leads to biases in sea surface temperature.
One reason, we argue, is that current parameterizations are
missing key surface-wave processes that force Langmuir
turbulence that deepens the OSBL more rapidly than steady
wind forcing. Scaling arguments are presented to identify two
dimensionless parameters that measure the importance of
wave forcing against wind forcing, and against buoyancy
forcing. A global perspective on the occurrence of waveforced
turbulence is developed using re-analysis data to
compute these parameters globally. The diagnostic study
developed here suggests that turbulent energy available for
mixing the OSBL is under-estimated without forcing by
surface waves. Wave-forcing and hence Langmuir turbulence
could be important over wide areas of the ocean and in all
seasons in the Southern Ocean. We conclude that surfacewave-
forced Langmuir turbulence is an important process in
the OSBL that requires parameterization.
|Date Deposited:||05 Oct 2012 10:34|
|Last Modified:||25 Oct 2016 01:44|
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