CHAPTER
MOVEMENTS OF OCEAN WATER
T
he ocean water is dynamic. Its physical wavelength of the wave, the wave breaks. The
characteristics like temperature, largest waves are found in the open oceans.
salinity, density and the external Waves continue to grow larger as they move
forces like of the sun, moon and the winds and absorb energy from the wind.
influence the movement of ocean water. The Most of the waves are caused by the wind
horizontal and vertical motions are common driving against water. When a breeze of two
in ocean water bodies. The horizontal motion knots or less blows over calm water, small
refers to the ocean currents and waves. The ripples form and grow as the wind speed
vertical motion refers to tides. Ocean currents increases until white caps appear in the
are the continuous flow of huge amount of breaking waves. Waves may travel thousands
water in a definite direction while the waves of km before rolling ashore, breaking and
are the horizontal motion of water. Water moves dissolving as surf.
ahead from one place to another through ocean A wave’s size and shape reveal its origin.
currents while the water in the waves does not Steep waves are fairly young ones and are
move, but the wave trains move ahead. The probably formed by local wind. Slow and
vertical motion refers to the rise and fall of water steady waves originate from far away places,
in the oceans and seas. Due to attraction of possibly from another hemisphere. The
the sun and the moon, the ocean water is raised maximum wave height is determined by the
up and falls down twice a day. The upwelling strength of the wind, i.e. how long it blows and
of cold water from subsurface and the sinking the area over which it blows in a single direction.
of surface water are also forms of vertical Waves travel because wind pushes the
motion of ocean water. water body in its course while gravity pulls the
crests of the waves downward. The falling water
WAVES pushes the former troughs upward, and the
Waves are actually the energy, not the water
as such, which moves across the ocean surface.
Water particles only travel in a small circle as a
wave passes. Wind provides energy to the
waves. Wind causes waves to travel in the ocean
and the energy is released on shorelines. The
motion of the surface water seldom affects the
stagnant deep bottom water of the oceans. As
a wave approaches the beach, it slows down.
This is due to the friction occurring between
the dynamic water and the sea floor. And, when
the depth of water is less than half the Figure14.1 : Motion of waves and water molecules
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, MOVEMENTS OF OCEAN WATER 117
wave moves to a new position (Figure 14.1). is less as it is farther away, the centrifugal force
The actual motion of the water beneath the causes tidal bulge on the other side (Figure
waves is circular. It indicates that things are 14.2).
carried up and forward as the wave The ‘tide-generating’ force is the difference
approaches, and down and back as it passes. between these two forces; i.e. the gravitational
attraction of the moon and the centrifugal force.
Characteristics of Waves On the surface of the earth, nearest the moon,
Wave crest and trough : The highest and pull or the attractive force of the moon is greater
lowest points of a wave are called the crest than the centrifugal force, and so there is a net
and trough respectively. force causing a bulge towards the moon. On
Wave height : It is the vertical distance the opposite side of the earth, the attractive
from the bottom of a trough to the top of force is less, as it is farther away from the moon,
a crest of a wave. the centrifugal force is dominant. Hence, there
Wave amplitude : It is one-half of the wave is a net force away from the moon. It creates
height. the second bulge away from the moon. On the
Wave period : It is merely the time interval surface of the earth, the horizontal tide
between two successive wave crests or generating forces are more important than the
troughs as they pass a fixed point. vertical forces in generating the tidal bulges.
Wavelength : It is the horizontal distance
between two successive crests.
Wave speed : It is the rate at which the
wave moves through the water, and is
measured in knots.
Wave frequency : It is the number of waves
passing a given point during a one-
second time interval.
TIDES
The periodical rise and fall of the sea level, once
or twice a day, mainly due to the attraction of
the sun and the moon, is called a tide.
Movement of water caused by meteorological
effects (winds and atmospheric pressure
changes) are called surges. Surges are not
regular like tides. The study of tides is very
complex, spatially and temporally, as it has great
variations in frequency, magnitude and height. Figure14.2 : Relation between gravitational
The moon’s gravitational pull to a great forces and tides
extent and to a lesser extent the sun’s
gravitational pull, are the major causes for the The tidal bulges on wide continental
occurrence of tides. Another factor is centrifugal shelves, have greater height. When tidal bulges
force, which is the force that acts to counter hit the mid-oceanic islands they become low.
balance the gravity. Together, the gravitational The shape of bays and estuaries along a
pull and the centrifugal force are responsible coastline can also magnify the intensity of tides.
for creating the two major tidal bulges on the Funnel-shaped bays greatly change tidal
earth. On the side of the earth facing the moon, magnitudes. When the tide is channelled
a tidal bulge occurs while on the opposite side between islands or into bays and estuaries
though the gravitational attraction of the moon they are called tidal currents.
2022-23
MOVEMENTS OF OCEAN WATER
T
he ocean water is dynamic. Its physical wavelength of the wave, the wave breaks. The
characteristics like temperature, largest waves are found in the open oceans.
salinity, density and the external Waves continue to grow larger as they move
forces like of the sun, moon and the winds and absorb energy from the wind.
influence the movement of ocean water. The Most of the waves are caused by the wind
horizontal and vertical motions are common driving against water. When a breeze of two
in ocean water bodies. The horizontal motion knots or less blows over calm water, small
refers to the ocean currents and waves. The ripples form and grow as the wind speed
vertical motion refers to tides. Ocean currents increases until white caps appear in the
are the continuous flow of huge amount of breaking waves. Waves may travel thousands
water in a definite direction while the waves of km before rolling ashore, breaking and
are the horizontal motion of water. Water moves dissolving as surf.
ahead from one place to another through ocean A wave’s size and shape reveal its origin.
currents while the water in the waves does not Steep waves are fairly young ones and are
move, but the wave trains move ahead. The probably formed by local wind. Slow and
vertical motion refers to the rise and fall of water steady waves originate from far away places,
in the oceans and seas. Due to attraction of possibly from another hemisphere. The
the sun and the moon, the ocean water is raised maximum wave height is determined by the
up and falls down twice a day. The upwelling strength of the wind, i.e. how long it blows and
of cold water from subsurface and the sinking the area over which it blows in a single direction.
of surface water are also forms of vertical Waves travel because wind pushes the
motion of ocean water. water body in its course while gravity pulls the
crests of the waves downward. The falling water
WAVES pushes the former troughs upward, and the
Waves are actually the energy, not the water
as such, which moves across the ocean surface.
Water particles only travel in a small circle as a
wave passes. Wind provides energy to the
waves. Wind causes waves to travel in the ocean
and the energy is released on shorelines. The
motion of the surface water seldom affects the
stagnant deep bottom water of the oceans. As
a wave approaches the beach, it slows down.
This is due to the friction occurring between
the dynamic water and the sea floor. And, when
the depth of water is less than half the Figure14.1 : Motion of waves and water molecules
2022-23
, MOVEMENTS OF OCEAN WATER 117
wave moves to a new position (Figure 14.1). is less as it is farther away, the centrifugal force
The actual motion of the water beneath the causes tidal bulge on the other side (Figure
waves is circular. It indicates that things are 14.2).
carried up and forward as the wave The ‘tide-generating’ force is the difference
approaches, and down and back as it passes. between these two forces; i.e. the gravitational
attraction of the moon and the centrifugal force.
Characteristics of Waves On the surface of the earth, nearest the moon,
Wave crest and trough : The highest and pull or the attractive force of the moon is greater
lowest points of a wave are called the crest than the centrifugal force, and so there is a net
and trough respectively. force causing a bulge towards the moon. On
Wave height : It is the vertical distance the opposite side of the earth, the attractive
from the bottom of a trough to the top of force is less, as it is farther away from the moon,
a crest of a wave. the centrifugal force is dominant. Hence, there
Wave amplitude : It is one-half of the wave is a net force away from the moon. It creates
height. the second bulge away from the moon. On the
Wave period : It is merely the time interval surface of the earth, the horizontal tide
between two successive wave crests or generating forces are more important than the
troughs as they pass a fixed point. vertical forces in generating the tidal bulges.
Wavelength : It is the horizontal distance
between two successive crests.
Wave speed : It is the rate at which the
wave moves through the water, and is
measured in knots.
Wave frequency : It is the number of waves
passing a given point during a one-
second time interval.
TIDES
The periodical rise and fall of the sea level, once
or twice a day, mainly due to the attraction of
the sun and the moon, is called a tide.
Movement of water caused by meteorological
effects (winds and atmospheric pressure
changes) are called surges. Surges are not
regular like tides. The study of tides is very
complex, spatially and temporally, as it has great
variations in frequency, magnitude and height. Figure14.2 : Relation between gravitational
The moon’s gravitational pull to a great forces and tides
extent and to a lesser extent the sun’s
gravitational pull, are the major causes for the The tidal bulges on wide continental
occurrence of tides. Another factor is centrifugal shelves, have greater height. When tidal bulges
force, which is the force that acts to counter hit the mid-oceanic islands they become low.
balance the gravity. Together, the gravitational The shape of bays and estuaries along a
pull and the centrifugal force are responsible coastline can also magnify the intensity of tides.
for creating the two major tidal bulges on the Funnel-shaped bays greatly change tidal
earth. On the side of the earth facing the moon, magnitudes. When the tide is channelled
a tidal bulge occurs while on the opposite side between islands or into bays and estuaries
though the gravitational attraction of the moon they are called tidal currents.
2022-23
