Geoscience Reference
In-Depth Information
2007
,
2009
,
2010
;
Black
et al.
,
2007
;
Stiassnie
et al.
,
2007
;
Vakhguelt
,
2007
;
Troitskaya
& Rybushkina
,
2008
;
Rastigejev
et al.
,
2011
;
Soloviev & Lukas
,
2010
, among others, see
also
Section 7.3.5
for a relevant discussion). Most often, these studies have been inter-
preting dynamic and thermodynamic influences of the suspended spray. As discussed in
Section 9.1.2
, the spray models in this regard can be approximately subdivided into four
groups in terms of the physics which they imply. That is, the effect of damping the near-
surface atmospheric turbulence due to suspended spume (
Barenblatt
et al.
,
2005
;
Makin
,
2005
;
Kudryavtsev & Makin
,
2010
;
Rastigejev
et al.
,
2011
), the momentum-balance effect
of the spume acceleration (
Andreas & Emanuel
,
2001
;
Andreas
,
2004
), the rain-like effect
of damping the short waves by the droplets falling back down on the wavy surface (
Andreas
,
2004
), and the thermodynamic effects of wave-induced-pressure damping by suspended
droplets (
Vakhguelt
,
2007
).
In addition to the spume models, it has been shown that aerodynamic effects can also
cause relative or even absolute reduction of the sea drag. One of such effects is the full flow
separation of strong winds over steep waves (e.g.
Donelan
et al.
,
2004
,
2006
;
Kudryavtsev
& Makin
,
2007
). Such separation causes relative reduction of the wave-induced pressure
which is then accompanied by a decreased wind-energy input to the waves and therefore
results in the wind effectively experiencing a smaller sea drag. Such a reduction depends
on a combination of high winds and steep waves and can occur at moderate wind speeds
as low as
U
10
∼
s(
Donelan
et al.
,
2006
), progressively increasing towards higher
winds. To avoid confusion, it should be mentioned again that in benign conditions the
full-flow separation and the separation due to wave breaking lead to opposite effects in
terms of the wind input and sea drag (
Donelan
et al.
,
2006
;
Babanin
et al.
,
2007b
, and
Section 8.3
).
Additionally, in the case of the full-flow separation, a part of the wave profile will now
be residing under the separated flow and thus will not contribute to the total sea drag.
This may be essential if a proportion of short waves, riding this wave, is excluded from
the wind-wave interaction or eliminated this way, because the short waves support most
of the sea drag (
Kudryavtsev & Makin
,
2007
). Qualitatively, this effect is similar to that of
the rain-like droplets mentioned above (
Andreas
,
2004
).
Another type of aerodynamic model was suggested by
Troitskaya & Rybushkina
(
2008
).
This is a quasi-linear model based on Reynolds equations closed through the eddy viscos-
ity which takes into account the viscous sublayer. Wave-induced disturbances in the air
are treated in the linear context, whereas the mean wind profile is derived by consider-
ing nonlinear wind stresses. The model is similar to that of
Jenkins
(
1992
,
1993
), but is
extended to directly incorporate the contribution of the short-wave spectrum tail, rather
than to parameterise it.
This is the only model of the sea-drag saturation which does not rely on wave breaking to
bring about features which then lead to the reduction of the drag. This original theoretical
approach required neither sea spray nor flow separation.
While being conceptually different, however, in terms of the physics which eventually
leads to drag reduction and saturation, this model is similar to the sea-spray model of the
12 m
/
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