Fourth Study Conference on BALTEX Scala Cinema Gudhjem

The vertical integrated dissipation rate of the surface
dissipation regime is balanced by the flux of turbulent
kinetic energy through the sea surface (but is larger than
8u*^3 according to Oakey and Elliott, 1982). This flux was
found to be not significantly different from the energy loss
of surface waves by wave breaking according to Longuett-
Higgins (1969) or Phillips (1985).
The surface dissipation regime can be described by the
3
kz
ε ( z) = ε
relation
oe
αu*
, where ε = and k is
o
3H
the characteristic wave number of the wind waves
k =
g
2
U10
. H sig is the significant wave height,
sig
u
2
*
τ
=
ρ
with the wind stress τ and the density of sea water ρ0 and the
wind velocity at 10 m height above the sea surface U 10.
Depth [m]
REYNOLDS 08/2001
0
-5
-10
-15
-20
-25
-30
Epsilon [W/kg] (color) - Temperature [°C] (contour)
31.08.2001 01.09.2001 02.09.2001 03.09.2001 04.09.2001 05.09.2001 06.09.2001 07.09.2001
Figure 2. Isopleths of dissipation of turbulent kinetic
energy (grey scale coded) and water temperature (contour
lines) during the cruise. The gaps are due to technical
problems with the stern anchor of the research vessel.
The normalised dissipation rate measured in the surface
regime is shown in Figure 3.
Figure 3. Profiles of turbulent kinetic energy dissipation
normalised with respect to depth and dissipation.
The vertical integrated turbulent dissipation during strong
buoyancy loss in autumn 2002 was not balanced by the loss
of potential energy loss through surface fluxes. There are
indications that the corresponding potential energy was
provided by differential advection due to horizontal density
gradients.
o
- 64 -
1E-004
5E-005
2E-005
1E-005
5E-006
2E-006
1E-006
5E-007
2E-007
1E-007
5E-008
2E-008
1E-008
5E-009
2E-009
1E-009
5E-010
References
Agrawal, Y. C., E. A. Terray, M. A. Donelan, P. A.
Hwang, A. J. Williams III, W. M. Drennan, K. K.
Kahma, and S. A. Kitaigorodskii, Enhanced
dissipation of kinetic energy beneth surface waves.
Nature, 359, 219-220, 1992.
Anis, A. and J. N. Moum, Surface Wave – Turbulence
Interactions: Scaling ε(z) near the sea surface. J. Phys.
Oceanogr., 25, 2025 – 2045, 1995.
Longuett-Higgins, M. S., On wave breaking and the
equilibrium spectrum of wind-generated waves. Proc.
Roy. Soc. A., 310, 151-159, 1969.
Oakey, N. S. and J. A. Elliott, Dissipation within the
surface mixed layer. J. Phys. Oceanogr., 12, 171-185,
1982.
Phillips, O. M., Spectral and statistical properties of the
equilibrium range in wind-generated gravity waves. J.
Fluid Mech. 156, 505-532, 1985
Prandke, H., K. Holtsch, and A. Stips, MITEC technology
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measuring system MSS. Tech. Rep. EUR 19733 EN,
European Commission, 2000.