SEA SURFACE FORECASTING
The task of forecasting various elements of the sea
surface is the responsibility of senior Aerographers
Mates filling a variety of billets.
Aboard carriers, sea condition forecasts for flight
operations, refueling, or underway replenishment must
be provided on a routine basis. Staffs of larger facilities
will generally provide surf forecasts for amphibious
operations, while at air stations that support search and
rescue (SAR) units, you maybe called upon to provide
forecasts of sea conditions and surface currents.
Therefore, it is important that you be familiar with these
elements and be able to provide forecasts as necessary.
In this chapter, we will discuss sea surface
characteristics and the forecasting of sea waves, swell
waves, surf, and surface currents. Now lets consider
sea surface characteristics.
SEA SURFACE CHARACTERISTICS
LEARNING OBJECTIVES: Describe the basic
principles of ocean waves. List and describe
the properties that all waves have in common.
Define additional terms used in sea surface
forecasting. Explain wave spectrum in terms of
wave frequency, energy, and wind speed.
To accurately forecast sea conditions it is necessary
to understand the process of wave development, the
action that takes place as the energy moves, and to have
an understanding of the various properties of waves.
In this section, we will discuss this background
information and the terminology used. A complete
understanding of these terms is necessary to produce the
most usable and accurate sea condition forecast.
BASIC PRINCIPLES OF OCEAN WAVES
Ocean waves are advancing crests and troughs of
water propagated by the force of the wind. When winds
start to blow, the frictional effect of the wind on the water
creates ripples that form more or less regular arcs of long
radii. As the wind continues to blow, the ripples increase
in height and become waves.
A wave is visible evidence of energy moving in an
undulating motion through a medium, such as water. As
the energy moves through the water, there is little mass
motion of the water in the direction of travel of the wave.
This can best be illustrated by tying one end of a rope to
a pole or other stationary object. When the free end of
the rope is whipped up and down, a series of waves
moves along the rope toward the stationary end. There
is no mass motion of the rope toward the stationary end,
only the energy traveling through the medium, in this
case the rope.
A sine wave is a true rhythmic progression. The
curve along the centerline can be inverted and
superimposed upon the curve below the centerline. The
amplitude of the crest is equal to the amplitude of the
trough, and the height is twice that of the amplitude.
Sine waves are a theoretical concept seldom observed
in reality. They are used primarily in theoretical
groundwork so that other properties of sine waves may
be applied to other types of waves such as ocean waves.
Principles of other types of waves are modified
according to the extent of deviation of their properties
from those of sine waves.
Waves that have been created by the local wind are
known as sea waves. These waves are still under the
influence of the local wind and are still in the generating
area. They are composed of an infinite number of sine
waves superimposed on each other, and for this reason
they have a large spectrum, or range of frequencies.
Sea waves are very irregular in appearance. This
irregularity applies to almost all their properties. The
reason for this is twofold: first, the wind in the
generating area (fetch) is irregular both in direction and
speed; second, the many different frequencies of waves
generated have different speeds. Figure 6-1 is a typical
illustration of sea waves. The waves found in this aerial
photograph are irregular in direction, wave length, and
As the waves leave the generating area (fetch) and
no longer come under the influence of the generating
winds they become swell waves. Because swell waves
are no longer receiving energy from the wind, their
spectrum of frequencies is smaller than that of sea
waves. Swell waves are also smoother and more regular