East Asia and Western Pacific METEOROLOGY AND CLIMATE

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laboratory,
momentum flux to waves.
and obtain the wave drag which represents the portion of
an estimation for the oceanic condition.
On the basis of these results, we have made
The results in terms of the
ratio between wave-drag and wind-stress coefficients, C /C- , are
shown in Fig. 4.
This ratio, therefore, represents the fraction of
momentum flux used in producing waves at different nondimensional
2
fetches gL/U.Q, and under different wind velocities. At open sea,
only 10% of the wind stress is used for wave generation; at short
fetches, this is shown in the figure to be very different, especially
under low winds.
Interpretations of Remote Sensing Signals
Let me give you two examples in the area of marine remote sensing.
You have used the sea-surface temperature (SST) for years and in many
cases interchangeably with the subsurface temperature.
The difference
between these two temperatures is generally considered to be less than
1°C, although you realize that there is a cool skin over the sea surface,
the so-called thermal sublayer (Wu 1985b) .
We find that the
general concept about the thermal sublayer adopted from studies over
the solid surface is not applicable over the air-sea interface.
nondimensional thickness of the thermal sublayer generally expressed as
* "" $ t u * w A' does not nave a constant value, where u^ is the friction
velocity of currents and v the kinematic viscosity of water; see Fig.
5. The difference between the sea-surface and the subsurface tempera-"
ture (AT) depends also on the heat flux across the sea surface (Q) as,
The
AT - AQz//c p pu^w [2]
where c p and p are respectively the specific heat and density of
water. The sea-surface-temperature deviation is seen to vary rather
strongly with the wind velocity, especially so at low winds. This
importance should be further emphasized because most of the heat flux
in the global sense is from the tropical area, where the wind is
generally very low.
Now let us turn to another area of remote sensing, which along with
SST excite greatly the atmospheric scientists and oceanographers. It is
the mapping of the sea-surface wind velocity from space. This technique
is closely related to Bragg scattering of microwaves from ripples not