Chemistry Reference
In-Depth Information
struction of a coherent film-covered surface. It is shown using the data of
Gemmerich and Hasse (1992) that a slick can easily suppress small-scale
convective motion in the surface layer. Thus the heat transport through the
sea surface is influenced by surface films, as found experimentally (Jarvis
1962).
2. Some ''simple'' case studies
In order to understand how surface slicks are formed and how they are
broken up, it is necessary to take into account a number of elementary
processes and how they work in combination. This paper does not pretend
to present anything like a complete list of these processes, nor does it have
much to say about their interaction. What is intended is a simple-minded
discussion on a few effects that are felt to be of importance to establish a
more coherent description of slicks.
In the following three case studies with simplified geometry and flow
are considered. Two of them are simple theoretical investigations using
standard hydrodynamic theory, while the third one is based on a very in-
teresting experiment carried out by Mockros and Krone (1968).
2.1. Tearing of a continuous film
Consider a piece of the ocean covered with a monolayer with film pressure
3{V
w
-
V, where V
w
and V are the surface tensions of pure water and film,
respectively. We further assume that the film is stagnant. Beneath the film,
however, there is a horizontal motion (taken to be in the x-direction) with a
corresponding boundary layer. Consequently, there is a tangential viscous
stress, W
visc
, on the film which must be balanced by a gradient in 3.
d
3
d
V
W
(1)
visc
dx
dx
We take the motion below the boundary layer to be spatially periodic with
up-welling and down-welling zones, and model the flowfield
v
just below
the boundary layer as
v
U
k
(sin
kx
,
0
kz
cos
kx
)
(2)
where
z
is the vertical coordinate (see Figure 1), and there stagnation lines
parallel to the y-axis at
kx
= 0, rS, r2S..... are assumed.
