Formation of waves, ocean currents and tides.

1. IIUI INTERNATIONAL ISLAMICUIVERSITY ISLAMABAD
PRESENTED BY: MAHBOOBULLAH
PRESSENTEDTO : .
How waves, currents & tides are
FORMED?

2. Waves
The ocean isnever still.Whether observingfromthebeach or a boat,weexpect
to see waves on the horizon. Waves are created by energy passing through
water,causing it to movein a circular motion.However,waterdoesnot actually
travelin waves. Waves transmitenergy, not water, across the ocean and if not
obstructedby anything,they havethepotentialto travelacrossanentireocean
basin.
Waves are most commonly caused by wind. Wind-driven waves, or surface
waves, are created by the friction between wind and surface water. As wind
blows across the surface of the ocean or a lake, the continual disturbance
creates a wavecrest. These types of waves arefound globally across the open
ocean and along the coast.
More potentially hazardous waves can be caused by severe weather, like a
hurricane. The strong winds and pressure from this type of severe storm
causes storm surge, a series of long waves that are created far from shore in
deeper waterand intensifyas they movecloser to land. Other hazardouswaves
can be caused by underwater disturbances that displace large amounts of
waterquickly suchas earthquakes,landslides,orvolcanic eruptions.Thesevery
long waves arecalled tsunamis. Stormsurgeand tsunamis arenot the types of
waves you imagine crashing down on the shore. These waves roll upon the
shore like a massive sea level rise and can reach far distances inland.
The greatmajority of large breakers seen at a beach result fromdistantwinds.
Five factors influence the formation of the flow structures in wind waves:
Wind speed or strength relative to wave speed—the wind must be moving
faster than the wave crest for energy transfer

3. The uninterrupted distance of open water over which the wind blows without
significant change in direction (called the fetch)
Width of area affected by fetch (at right angle to the distance)
Wind duration — the time for which the wind has blown over the water.
Water depth
All of these factors worktogether to determinethe sizeof the water waves and
the structure of the flow within them.
The main dimensions associated with waves are:
Wave height (vertical distance from trough to crest)
Wave length (distance from crest to crest in the direction of propagation)
Waveperiod (timeintervalbetween arrivalof consecutivecrestsata stationary
point)
Wave propagation direction
A fully developed sea has the maximum wave size theoretically possible for a
wind of a specific strength, duration, and fetch. Further exposure to that
specific wind could only cause a dissipation of energy due to the breaking of
wavetops and formation of "whitecaps". Waves in a given area typically have a
rangeof heights. For weather reporting and for scientific analysis of wind wave
statistics, their characteristic height over a period of time is usually expressed
as significant wave height. This figure represents an average height of the
highest one-third of the waves in a given time period (usually chosen
somewherein the rangefrom20minutes to twelvehours),orin a specific wave
or storm system. The significant wave height is also the value a "trained
observer" (e.g. froma ship's crew) would estimatefromvisualobservation of a
sea state. Given the variability of waveheight, the largestindividual waves are

4. likely to be somewhatless than twice the reported significant waveheight for
a particular day or storm.
Currents
Ocean currents are a
continuous or
permanent movement
of ocean water. Some
ocean currents are
temporary, while
others take centuries
to complete a circle of
the globe. The friction
created when wind blow over the water surfaceproduces ocean currents. Due
to this friction, ocean currents are slower than winds. The forces that
determine the direction of these currents are gravity, wind, variation in water
density, and tides. Ocean currents play an important role in determining the
climates of many regions of the Earth. These currents also influence the
navigation and the nature and quality of marine organisms.
On the basis of temperature ocean currents are classified as warm and cold
water currents. Warmwater currents formnear theequator creating a warmer
climate near the coastlines as it travels towards the poles. Cold water currents
on the other hand formnear the poles and traveltowards theequator creating
cooler climate near the coastlines.

5. Types of Ocean Currents
There are two basic types of ocean currents: SurfaceCurrents and Deep Water
Currents.
Surface Ocean Currents
Surface ocean currents are the movement of water on or near the surfaceof
oceans. They are primarily driven by winds, resulting in horizontaland vertical
movement. These winds blow in the same direction all the time making the
water move in the same direction. Though surface currents flow in regular
patterns, they arehowever notsame. Whilesome aredeep and narrow, others
are shallow and wide measuring only 50 to 100 meters deep. Though shallow,
they are important as they influence world’s climate and weather and in
distributing heat and nutrients around the planet.
Since surfacecurrents aregenerated by wind, their patterns aredetermined by
wind direction and the Coriolis Effect. Surface currents flow clockwise in

6. Northern Hemisphere and counterclockwise in Southern Hemisphere. The
loops that are formed by the circulating currents are called gyres.
Deep currents
Deep currentsarethe movementof waterbelow thesurfaceof theocean. They
are the result of density differences in water which is controlled by the
difference in temperature and salinity. The difference in temperature and
salinity change the density of seawater. Deep water currents, therefore, are
thermohalinecurrents.Thetermthermo means heatand haline means salinity.
When water freezes into ice, it leaves behind salt making the underlying water
salty. This extremely cold, saline water is very dense and sinks to the seafloor.
This sinking is called downwelling. It helps sustain life in the depth of oceans.
Downwelling transports ocean rich surface water to deeper waters providing
oxygen-rich waters. These mixtures of water influence the decomposition in
surface waters.
When the warm water moves toward the equator, it becomes less dense and
floats to the surface. This process is called upwelling. Upwelling takes place
along the coast when the wind forces dense water from below to replace the
less dense water at the surface. During upwelling, it brings vital nutrients from
the ocean floor to the surface waters. It brings up nutrients from the ocean
floor to the surface. These nutrients collected at the bottom of the ocean
provide nutrients to planktons and support life in the equatorial oceans.
Importance of Ocean Currents to Climate
Ocean currents are the regulators of the thermal environment at the earth’s
surface. They help in exchangeof heat between the low and high latitudes. The
absence of currents would result in the temperatures being very hot at the

7. equator and severely cold towards the pole. The moderating ocean
temperaturenear the coastreduces annualcoastaltemperatures. When winds
from the warm water blow over cooler land there is large cloud and frequent
precipitation. A combination of cool currentwith descending high-pressureair
systemresults in an extremely dry coastal climate. The Gulf Stream, the North
Atlantic Drift and Northwestern Europe have a mild climate while Chile, Peru
and southwest Africa extremely dry coastal climate.
Tides
High tide (left) and low tide (right) in the Bay of
Fundy in Canada. Image credit: Wikimedia
Commons, Tttrung. Photo by Samuel Wantman.
High tides and low tides are caused by the moon. The moon's gravitationalpull
generates something called the tidal force. The tidal force causes Earth—and
its water—to bulge out on the side closest to the moon and the side farthest
from the moon. These bulges of water are high tides.
As the Earth rotates, your region of Earth passes through both of these bulges
each day. When you're in one of the bulges, you experience a high tide. When
you're not in one of the bulges, you experience a low tide. This cycle of two
high tides and two low tides occurs mostdays on mostof the coastlines of the
world.

8. This animation shows the tidal force in a view of Earth from the NorthPole. As regions ofEarth pass through the bulges,
they can experiences a high tide.
Tides are really all about gravity, and when we'retalking about the daily tides,
it's the moon's gravity that's causing them.
As Earth rotates, the moon's gravity pulls on differentparts of our planet. Even
though the moon only has about 1/100th the mass of Earth, since it's so close
to us, it has enough gravity to move things around. The moon's gravity even
pulls on the land, but not enough for anyone to tell (unless they use special,
really precise instruments).
When the moon'sgravitypulls on the waterin the oceans,however,someone's
bound to notice. Water has a much easier time moving around, and the water
wants to bulge in the direction of the moon. This is called the tidal force.
Because of the tidal force, the water on the side of the moon always wants to
bulge out toward the moon. This bulge is what wecall a high tide. As your part
of the Earth rotates into this bulge of water, you might experience a high tide.

9. An illustrationof the tidal force, viewedfrom Earth's North Pole. Water bulges toward the moonbecauseof gravitational
pull. Note: The moon is not actually this close to Earth.
Onething to note, however, is that this is justan explanation of the tidal force—
not the actual tides.Inreal life, the Earth isn't a global ocean, coveredin an even
layer of water. There are seven continents, and that land gets in the way. The
continents prevent the water from perfectly following the moon's pull. That's why in
someplaces,the differencebetween high and low tideisn't verybig,and in other
places, the difference is drastic.
The ocean also bulges out on the side of Earth opposite the moon.
If the moon's gravity is pulling the oceans toward it, how can the ocean also
bulge on the side of Earth away fromthe moon? Itdoes seem a little weird. It's
all because the tidal force is a differential force—meaning that it comes from
differences in gravity over Earth's surface. Here's how it works:

10. On the side of Earth that is directly facing the moon, the moon's gravitational
pull is the strongest. The water on that side is pulled strongly in the direction of
the moon.
On the side of Earth farthest from the moon, the moon's gravitationalpull is at
its weakest. At the center of Earth is approximately the average of the moon's
gravitational pull on the whole planet.
Arrows representthe force of the moon's gravitational pull on Earth. To getthe tidal force—the force that causes the
tides—we subtract this average gravitational pullon Earth from the gravitational pull at eachlocationon Earth.