003 008-ocean motions

Waves
1. A Wave is a rhythmic movement that carries
energy through matter or space.
2. When a wave passes through the ocean, individual
water molecules move up and down in a circular
motion but they do not move forward or backward
3. As waves approach shore, the wave length
decreases and wave height increases
4. When a wave breaks against the shore, the crest
outruns the trough and the crest collapses-this is
called a breaker (water moves forward and
backward at this point).

Waves are moving energy
• Forces cause waves to move along air/water
or within water
– Wind (most surface ocean waves)
– Movement of fluids with different densities
•Internal waves often larger than surface
waves
– Mass movement into ocean
•Splash waves

• Seafloor movement
– Tsunami or seismic sea wave
• Gravitational attraction Earth, Moon,
Sun
– Tides
• Human activities
– Wakes of ships
– Explosions

Progressive waves
• Longitudinal
– “Push-pull”
• Transverse
– Side-to-side or up-and-down
• Orbital
– Circular orbit
– Ocean surface waves

Wave characteristics
• Crest, trough
– Wave height is proportional to energy
• Wave length
• Wave height/wave length = wave
steepness
– Waves break when H/L is 1/7
• Wave period, frequency

Wave characteristics
• Wave base is 1/2 wave length
– Negligible water movement due to waves
below this depth Fig.9-6a

Deep-water wave
•Depth of water is greater than
1/2 wavelength
•Speed of wave form (celerity) is
proportional to wavelength

Shallow-water wave
• Water depth is less than 1/20 wavelength
• Friction with seafloor retards speed
• Wave speed (celerity) is proportional to depth
of water
• Orbital motion is flattened

Transitional waves
• Water depth is 1/2 to 1/20 of
wavelength
• Characteristics of deep and shallow-
water waves
• Wave speed (celerity) is proportional
to both wavelength and depth of
water

Wave equations
• Wave speed = wavelength/period
–S = L/T
• Frequency = 1/period
–F = 1/T
• Wave speed (m/s) = 1.56 x period
–S = 1.56 x T

Surface ocean waves
• Most wind-driven
• Small wind-driven waves
–Capillary waves
• Larger wind-driven waves
–Gravity waves

Sea
• Storm at sea creates waves
• Wave energy depends on
– Wind speed
– Fetch
– Duration
• Chaotic mixture of different
wavelengths and wave heights

Wave dispersion
•Longer wavelength waves
outdistance shorter wavelength
waves
•Waves travel in groups or trains
with similar characteristics
•Swell made up of waves of similar
wavelength and period

Wave interference
• Constructive
–Wave heights increase
• Destructive
–Wave heights decrease
• Mixed
–Wave heights vary in wave train
(surf beat)

Interference illustrated
Fig. 9-14

Rogue waves
• Unusually large waves
– Constructive interference
– Waves meet strong ocean current
Fig. 9-16

Shoaling waves
•Waves reach surf zone
–Wave speed decreases
–Wave length decreases
–Wave height increases
•Wave steepness 1/7, wave breaks
•Surface tension no longer able to hold
wave together

Breakers
•Spilling
–Gentle beach slope
•Plunging
–Moderately steep slope
•Surging
–Abrupt slope

Wave refraction
• Shoaling waves bend so wave fronts
approach a shore nearly parallel
Fig. 9-19a

• Wave energy
focused on
headland
• Wave energy
dispersed over
bay
Fig. 9-19b

Wave diffraction
• Wave energy
transferred
around or
behind barriers
Fig. 9-20

Wave reflection
•Waves bounce back from steep
slopes or seawalls
•Reflected wave may
constructively interfere with other
waves

Standing waves
• Two waves with same wavelength
moving in opposite directions
• Node – no vertical movement
–Greatest horizontal movement
• Antinode – greatest vertical
movement

Tsunami or seismic sea wave
• Caused by sudden changes in
volume of ocean basin
–Mainly submarine faults
–Volcanic eruptions
–Submarine landslides

Tsunami
• Very long wavelength
• Travels fast
• Raises sea level as crest shoals
–Trough causes sea level to fall
• Disastrous for infrastructure at
coasts
• Possibly much loss of life

Tsunami warning system
•Monitor seismic activity
•Monitor changes in unusual wave
activity
•Warning
–People evacuate

5. Parts of a Wave
a. Crest – highest point of a wave
b. Trough – lowest point of a wave
c. Wave Height – vertical distance
between the crest and the
trough
d. Wavelength – horizontal
distance between two crests or
two troughs

Wavelength
Wave
Height
Crest
Trough
Still Water
Wave Parts
PLEASE DRAW AND LABEL

5. Effects of Waves on Shore
a. Longshore current- As waves come into
shore, water washes up the beach at an
angle, carrying sand grains. The water and
sand then run straight back down the beach.

Types of Breaking Waves:
• Plunging breaker
• Spilling breaker
• Surging breaker
Factors that determine the position and
nature of the breaking wave:
• Slope
• Contour
• Composition
Waves approaching shore

a gradual sloping bottom generates a milder wave

• doesn't break, because it never reaches critical
wave steepness
• breaker diminishes in size and looses momentum
• Found on beach with a very steep or near vertical
slope
Surging Breaker

Sunset Beach
What type wave are these?
Waikiki

Wave Refraction- when a wave approaches an inclined surface
(shore) from an angle, the wave slows and bends, paralleling the
shoreline, creating odd surf patterns

Wave Diffraction- Propagation of a wave around an obstacle

Wave Reflection- a progressive wave striking a vertical barrier and being
reflected in the direction from where they came
The Wedge, Newport Harbor, Ca
waves

5b. Rip Current-long ridges or piles of
sand create sand bars. A break in a
sand bar allows a fast-moving narrow
stream of water through

6. Cause of Waves
a. Wind
– When wind blows across a body of water,
friction causes the water to move along with the
wind.
– Wave Height depends on –
• Wind speed
• Distance over which the wind blows
• Length of time the wind blows

6b. Earthquakes- Waves caused by
earthquakes are called Tsunamis
i. Tsunamis were once called
Tidal waves, but they have
nothing to do with the
tides.
ii. They are produced by
earthquakes and other
seismic disturbances.
That’s why they’re also
called seismic sea waves.
iii. Sudden outflow of water
then it returns much
higher

iii. Tsunamis are very long, fast
moving waves!
• They can have wavelengths of 150
miles, wave heights of 100 ft and move
as fast as 450 mph (jet speed!).

Fault displacement under water
displaces water, water moves to fill
vacuum, generating large waves.

A. Ocean water contains horizontal,
stream-like movements of water
called ocean currents.
B. Affected by weather, Earth’s
rotation, and the position of the
continents.
C. Importance:
1. moves drifting organisms from
place to place – plankton,
disperse young
2. carries eggs and larvae of
organisms that have external
fertilization
3. brings food, oxygen
4. carries away waste, pollutants
I. Currents (pgs. 84-88)

1. Surface Currents
a. Horizontal movements of ocean water caused
by wind and occurring at or near the ocean’s
surface are called surface currents.
b. Can reach depths of several hundred meters
and lengths of several thousand kilometers.
c. The Gulf Stream is one of the longest surface
currents, transporting 25 times more water
than all the rivers in the world combined.
d. Controlled by 3 factors:
 Global winds
 Continental barriers
 Coriolis Effect
D. Three Main Types

• Different winds cause
currents to flow in
different directions.
– The trade winds are
located just north and
south of the equator.
• In both hemispheres,
they push currents
westward across the
tropical latitudes.
– The westerlies are
located in the middle
latitudes.
d1. Global Winds

• The continents are another major influence on surface
currents.
– They act as barriers to these currents.
– When a surface current flows against a continent, the
current is deflected and divided.
d2. Continental Barriers

• As Earth rotates,
ocean currents and
wind belts curve.
– The curving of the
paths of ocean
currents and winds
due to Earth’s
rotation is called
the Coriolis Effect.
– The wind belts and
the Coriolis Effect
create huge circles
of moving water,
called gyres.
d3. Coriolis Effect

a. Stream-like movements of ocean water located
far below the surface are called deep currents.
b. Move much slower than surface currents.
c. Form as cold, dense water of the polar regions
sinks and flows beneath warmer ocean water.
• The density of ocean water if affected by
temperature and salinity.
– Decreasing temperature and increasing
salinity will increase the water’s density.
Cold water is more dense than warm
water!
2. Deep Currents

d. when combined with
surface currents, results in
conveyor belt movement of
water around globe

Ekman Transport
Definition – term given for the 90 degree
net transport of the surface layer due
to wind forces and Coriolis Effect.
First investigated in 1902 by

. Ekman motion theory
 In the northern hemisphere this
transport is at a 90 degree angle to the
right of the direction of the wind.
 In the southern hemisphere it occurs
at a 90 degree angle to the left of the
direction of the wind.
Ekman Spiral – Model
plotting the water layers at various
directions, speed and depth

Consequences of Ekman Transport
• Ekman affects picnocline layer
• Coastal Upwelling
– Cold surface water, high nutrients
– High phytoplankton productivity
– Great fisheries (Sahara bank, Peru)
• Coastal Downwelling
– Warm surface water, low nutrients
– Low phytoplankton
– Poor fisheries (Northern Brazil)

Pressure Gradient and Coriolis
equilibrium: Geostrophic currents

Geostrophic currents
Geostrophic currents
follow lines of equal
pressure / height

Open Ocean Surface Currents
Ekman surface transport

Open Ocean Geostrophic currents

Geostrophic currents and
continents

Upwelling and Downwelling
Convergence and Divergence
• Downwelling – Convergence
– Subtropical Gyres
– Sargasso Sea example of Geostrophic current
• Upwelling – Divergence

Oceanic Gyres
Western Boundary Currents
• Gulf Stream, Kuroshio,
Agulas currents
• Narrow (100 km)
• Deep (<2000 m)
• Swift (1.5 m/s)
• Warm
• High Volume
(50-75 Sv)
Eastern Boundary Currents
• California, Canary, Peru
currents
• Broad (1000 km)
• Shallow (<500 m)
• Sluggish (0.3 m/s)
• Cool
• Low Volume
(10-15 Sv)
1 Sverdrup = 100000 m3/s

Western Boundary Current
Intensification
Stronger Coriolis force at higher latitudes

Western Boundary Current
Intensification
Subtropical Gyres displaced to the West

Definition – upward movement of the deeper,
cooler waters toward the surface pushing surface
waters away from the shore due to the Ekman
Transport.
Description
Coriolis Effect moves water at right angles slightly
right of the direction the wind is blowing resulting in
surface currents pushing the surface waters
offshore.
When surface waters are pushed offshore, water
from below is drawn upward to replace them.
Upwelling

Caused by Waters Diverging away from a region.
Effects:-
Brings nutrient –rich waters to the surface
encouraging seaweed and phytoplankton
growth.
Moves drifting larvae long distances from their
natural habitat affecting population stability.

Downwelling
Definition – Surface waters move toward the
shore due to Ekman Transport and sink to the
bottom.
Remember: water is a fluid in constant motion; a
change in the distribution of water in one area is
accompanied by a compensating change in another
area.
Caused by a Waters Converging toward a region.

Upwelling and Downwelling
Diagram

Ekman spiral
Ekman spiral
describes the
speed and
direction of flow of
surface waters at
various depths
Factors:
Wind
Coriolis effect

Ekman transport
Ekman transport
is the overall water
movement due to
Ekman spiral
Ideal transport is
90º from the wind
Transport direction
depends on the
hemisphere

3. upwelling
a.wind blows, moves water away, causes new
water to rise up to replace it
b.brings up tiny ocean organisms, minerals,
and other nutrients from the deeper layers
of the water.

Equatorial
Upwelling
Coastal Upwelling

NB p. 19 Upwelling in the World Ocean

Look at the equator in the
Pacific Ocean.

What’s the difference between
Peru(A) and Colombia (B)?
B
A

The Monsoonal wind shifts in
Oman create very different
conditions.
August, 1999
Offshore winds: Upwelling
April, 1999
Onshore winds: Downwelling

Identifying upwelling on
satellite-derived maps
•Sea Surface Temperature
•Ocean Color

The deep water that surfaces in upwelling is cold;
by looking at Sea Surface Temperature maps we
can identify cool upwelled water versus hotter
surface water.

Upwelled water also contains nutrients (nitrate,
phosphate, silicate) and dissolved gases
(oxygen and carbon dioxide) that are not
utilized at depth because of a lack of sunlight.
Now on the surface, these nutrients and gases help to
fuel photosynthesis by small algae called
phytoplankton.

Phytoplankton photosynthesize using
specialized color pigments called chlorophyll.
Thus, “Ocean Color” maps are another way to
identify areas of upwelling. Where on this
ocean color map are high phytoplankton
concentrations?

Ecological and Economic effects
of upwelling:
• Upwelling leads to more phytoplankton
• More phytoplankton leads to more fish
• More fish lead to commercial fishing jobs
and to more seafood

Phytoplankton come in many shapes
and forms. Collectively they form
the base of oceanic food webs.
Without upwelling many of the
world’s fisheries would not thrive.

Even though upwelling areas account for
only 1% of the ocean surface, they
support 50% of the world’s fisheries.

Upwelling and Fisheries
Using this series of Sea Surface Temperature Maps from 1999, can
you determine areas/times for possible fisheries?
(Hint: Look at Peru’s coast in January and April. Look at the northwestern tip of Africa in
July and October.)
January April
July October

Equatorial Upwelling
The ocean around the equator receives the most sunlight. However, the
surface layer of the ocean around the equator shows up as a region relatively
cooler than surface layers of the surrounding oceanic regions.
Around the equator oceanic region there is such a concentration of biomass
that it can be seen from space.
What can explain these observations?
!Equatorial Upwelling!

The Physics of Equatorial Upwelling
On the earth there are trade winds that blow
in towards the equator from the northeast
starting at 30 N , and there are trade
winds which blow towards the equator
from the southeast starting at 30 S.
When these winds hit the surface of the ocean
they create an overall Ekman transport of
water perpendicular to the line of their
impact. These two trends meet at the
equator, in a region called the ITCZ
(Inter-tropical convergence zone)
Southwards is the direction of transport
perpendicular to the South East trade
wind, and northwards is the direction of
transport perpendicular to the North West
trade wind.
Therefore a continuous hole that must be
filled is created in the equatorial regions.
The hole is filled from below by an
upwelling of cool, nutrient rich water from
the bottom of the ocean. This overall
effect is called equatorial upwelling and it
is the reason for the cooling observed at
the equator.

The Chemical Consequences of
Equatorial Upwelling
This transport of water up from the
bottom of ocean brings with it
nutrients which sustain life which
have sunk down into the ocean.
Important nutrients brought up and
recycled by this continuous process
of equatorial upwelling include
carbon, nitrogen, and phosphorus.
Therefore the surface layer of the
equatorial oceanic region of the
world are especially rich in the
nutrients utilized by life, and this
region can support a greater
amount of biomass. The increase in
ability to support life is so
significant the biological layer
created by equatorial upwelling can
even be seen from space.

Coastal upwelling and
downwelling
Ekman transport moves surface water away
from shore, producing upwelling
Ekman transport moves surface water
towards shore, producing downwelling

Other examples of upwelling (Which one looks like San Diego?)

Coastal Upwelling
• Equatorward winds along a coastline lead to
offshore Ekman transport
• Mass conservation requires these waters
replaced by cold, denser waters
• Brings nutrients into surface waters creating
bloom

1. Currents can greatly
affect the climate in many
parts of the world.
– Warm-water currents:
• The Gulf Stream carries
warm water from the Tropics
to the North Atlantic Ocean.
– Cold-water currents:
For example: The California
current carries cold water
from the North Pacific Ocean
toward Mexico along the
western coast of the USA 
therefore, cooler climate
year-round than inland
states.
E. Currents and Climate

2. Every 2 to 12 years, the South Pacific
trade winds move less warm water to the
western Pacific than they usually do.
a. El Niño-Pacific Ocean trade winds slow and
almost stop which brings warmer conditions
and weak upwelling currents to the eastern
Pacific which hurts fishing in Peru
b. La Niña-winds blow stronger than normal
pushing warm water out and allowing cold
water in. A stronger upwelling occurs.

Time scales for ocean-atmosphere interaction
ATM delay:
days-weeks
ATM
response
Heating/cooling
Evaporation/precip
Momentum transfer
ATM forcing
OCN
responseOCN forcing
OCN delay:
Hours-days-decades
Boundary layer processes Equatorial Ocean
Dynamics:
ENSO, IOD
Seasonal MLvariations:
NAO?
Subtropical Gyre, Rossby
Waves, THC, MOC
Pacific/Atlantic Decadal
Variability
Tropical
cyclones
Surface waves
Diurnal Cycle
Madden-Julian
Oscillation
Tropical
Instability
Waves
days weeks Months/years Decades and beyond

Stratifikasi Temperatur Lautan

Stratifikasi Temperatur Lautan
 Surface Zone
– Mixed by wind
 Thermocline
driven waves and currents (2%)

Eckman Spiral and Transport
Figure 8-9

Edaran Termohalin Buana sebagai pemasok bahang ke
wilayah kutub, dengan lain kata
 Mengatur luasnya laut es di daerah tersebut
 Menentukan laju massa air laut dalam muncul ke permukaan
 Berperan dalam konsentrasi CO2 di atmosfir
Diduga, mencairnya lap. es dari Tanah Hijau yg tawar akan


mengganggu pembentukan massa air laut dalam. Ini
menyebabkan perubahan iklim di Eropa, yg dikenal
periode Younger Dryas.
sebagai
Waktu
2005)
Dalam
materi
transit yang diperlukan sekitar 1600 tahun (Primeau,
edaran tersebut, massa air membawa energi (bahang),
(padat, terlarut, gas) mengelilingi dunia.

Oleh karenanya: edaran ini berdampak besar terhadap iklim
dunia


ENSO
El Niño- Southern Oscillation

lah fenomen
El Niño- Southern
(ENSO)
Oscillation
El Niño ada
lautan dan atmosfer
–Sering disebut: ENSO
El Niño dari data SST
 SO diketahui dari data
curah hujan
a antara
angin dan

SEJARAH
Awal abad 20, Sir Gilbert Walker
menemukan pola hubungan
di barat dan timur pada data
muka laut kawasan pasifik.
Menyelidiki monsun di India
tekanan
tekanan
Dia menyebut pola ini sebagai
Southern Oscillation.”
“The

The Southern Oscillation
Sir Gilbert Walker
(1868-1958) Tahiti
Darwin

Southern Oscillation
(SOI)
Index
Sir Gilbert Walker
(1868-1958)

The Oceanic Connection
Jacob Bjerknes
(1897-1975)

Fase Indeks rendah biasanya
dihubungkan oleh kondisi
Late 1960s - Jacob Bjerknes
yang pertama dengan jelas
mengetahui deskripsi umur
badai di lintang sedang
–Kunci yang menghubungkan
antara perbedaan tekanan SO
dan air hangat El Niño
Bagian dari fenomena yang sama-
ENSO.

 El Nino & La Nina adalah anomali suhu
oCpermukaan laut dengan besar > 0.5
sepanjang S. Pasifik tropis
 Jika anomali tsb bertahan < 5 bln, maka
disebut sebagai KONDISI El-Nino atau La-
Nina
 Jika anomali tsb bertahan > 5 bln, maka
disebut sebagai EPISODE El-Nino atau La-
Nina

Ciri-ciri el nino
Tek. Udara naik di S. Hindia, Indonesia, dan Australia
Tek. Udara turun di Tahiti dan di seantero S. Pasifik tengah
dan timur
Jika anomali tsb bertahan > 5 bln, maka disebut sebagai
EPISODE El-Nino atau La-Nina
Angin pasat di Pasifik selatan melemah, atau mengarah ke
timur
Konveksi udara hangat dekat Peru, mengakibatkan hujan di
daerah2 padang pasir
Massa air hangat menyebar dari barat Pasifik dan S. Hindia
menuju Pasifik timur, membawa hujan, menyebabkan hujan
tinggi di daerah yang biasanya kering, dan kekeringan di
daerah yang ditinggalkan.







Kondisi Normal
Atmospheric and oceanic
disturbances in Pacific Ocean
–Tekanan udara sepanjang pasifik
ekuator lebih tinggi di bagian
–Angin pasat tenggara kuat
–Kolam air hangat di sisi barat
pasifik
–Termokilin lebih dalam di sisi
timur
barat
–Upwelling tidak terjadi di pantai
Peru

Atmospheric and oceanic disturbances
in Pacific Ocean
El Niño-Southern Oscillation (ENSO)
–Hangat (El Niño) and Dingin (La Niña)
–Tekanan Tinggi di timur pasifik melemah
–Angin Pasat melemah
–Kolam air hangat berpindah ke
–Termoklin lebih dalam di timur
–Downwelling
–Produktivitas biologi rendah
timur
pasifik
Corals particularly sensitive to warmer
seawater

Mekanisme terjadinya El-Nino
Berbagai teori yang berkembang:
Adanya lokasi hangat anomali di Pasifik timur
akan melemahkan beda suhu antara timur dan
barat, dan menyebabkan melemahnya Sirkulasi
Walker dan angin pasat (Bjerknes, 1969)
Angin pasat yang menguat akan membangun
kolom air hangat di bag. Barat, dan pelemahan
mendadak dari angin pasat akan mengalirkan
massa air hangat ke timur (Wyrtki, 1975). Tapi ini
tidak terjadi utk El-Nino 1982-83
1.
2.

Mekanisme terjadinya El-Nino-2
Recharge Oscillator: beberapa mekanisme disampaikan ttg
kolom air hangat di daerah ekuator, dan menyebar ke
lintang lebih tinggi karena El-Nino. Daerah yang lebih dingin
kemudian perlu di”charge” menjadi hangat lagi utk
beberapa tahun sebelum kejadian itu berulang
3.
Osilator di Barat Pasifik: Di barat pasifik, berbagai kondisi
cuaca dapat menyebabkan anomali angin barat, seperti
pasang siklon di utara dan selatan ekuator. Angin ini akan
melemahkan angin pasat, sebagai pemicu akhir terjadinya
El Nino
4.

Wilayah katulistiwa Pasifik dalam kondisi hampir El-Nino,
dengan berbagai variasi acak yang berdampak terjadinya El-
Nino. Pola cuaca atau kegiatan vulkanik sebagai contohnya
5.
MJO (Madden Julian Oscillation) merupakan sumber penting
terjadinya variabilitas yang menghasilkan percepetan
evolusi terjadinya El-Nino. Yaitu lewat fluktuasi angin
permukaan dan hujan di bagian barat dan tengah ekuator
Pasifik. MJO dapat menghasilkan gelombang Kelvin
ekuator. El-Nino juga dapat mempengaruhi MJO
6.

Kejadian vulkanik di daerah tropis dapat menimbulkan 3
tahun El-Nino, dan dilanjutkan dengan 3 tahun La-Nina
(Adams, Mann, dan Ammann, 2003, menggunakan data iklim
paleo)
7.
MJO (Madden Julian Oscillation) merupakan sumber penting
terjadinya variabilitas yang menghasilkan percepetan
evolusi terjadinya El-Nino. Yaitu lewat fluktuasi angin
permukaan dan hujan di bagian barat dan tengah ekuator
Pasifik. MJO dapat menghasilkan gelombang Kelvin
ekuator. El-Nino juga dapat mempengaruhi MJO
8.


 floods, mudslides
 drought, crop failure
 fires
 downpours, tornados
 cyclones
 coral reefs die
 no fish
 great fishing
 
 







el Niño—how does it affect us?

Indonesia 1997/1998
Populasi besar > 200juta
Negara Berkembang
Krismon 1997
–Kerusuhan sipil
–Perubahan pemerintahan
Habibie)
1998 (Suharto -

Deforestasi (Kalimantan
–Kebakaran ; kabut asap
kayu
Pertanian pengganti
& Sumatra)

Sawit (utama) + karet
Penting bagi ekonomi
Korporasi besar disalahkan
terhadap 80% kebakaran hutan
lahan
dan

1997 El Nino – menunda musim
hujan
–Tidak ada hujan dari mei - september
–Musim hujan terlambat 3-4 bulan
– mengurangi musim hujan (nop – mar)
Kebakaran berlanjut hingga April
1998
–Tak terkendali
–1.5 - 2 jt hektare hutan terbakar

Indian Ocean Dipole Mode
 Fenomena mirip seperti El-Nino (di S.
Pasifik) ternyata juga ditemui di S. Hindia,
yang diberi nama IDM
 Baru tahun 1999, fenomena ini ditemukan
oleh Yamagata dan Saji, yang disebut
sebagai DME (Dipole Mode Event)
 Karena ingin mengkaji musim panas yang
berlebih pada tahun 1994 di Jepang

Indian Ocean Dipole Mode-2
 Hubungan antara IDM dengan El-Nino
belum diketahui dengan pasti
 Hubungan antara keduanya tidak
sederhana
 DME dipercaya menjadi kunci untuk
menjelaskan mekanisme perubahan
iklim regional yang terjadi di S. Hindia
hingga S. Pasifik

6c. Gravitational force of the
Moon and Sun creates
Tides (pgs 96-100).
.
i. The rise and fall in sea level is
called a tide.
ii. One low-tide/high-tide cycle
takes about 12 hrs and 25 min.
iii. Tidal range is the difference in
ocean level between high-tide
and low-tide

What is the Tidal Range?
• HT = 30 ft, LT = 20 ft
• HT = 20 ft, LT = 12 ft
• HT = 50 ft, LT = 20 ft
10 ft
8 ft
30 ft

iv. Gravitational Effect of the
Moon
• Two big bulges of water form on
the Earth:
–one directly under the moon
–another on the exact opposite
side
• As the Earth spins, the bulges
follow the moon.
• These are normal daily tides

v. Gravitational Effect of the Sun
a. Spring Tides
–Earth, Moon, and Sun are lined up
and work together
–High Tides are higher and Low
Tides are lower than normal

b. Neap Tides
–Earth, Moon, and Sun form right
angles and work against each other
–High Tides are lower and Low Tides
are higher than normal

TIPE PASUT
Spring: 1 st. and 3 rd. quarters
Neap: new and full moon

Tipe pasang surut dapat
diketahui dengan pasti
dengan cara mendapatkan
bilangan/ konstanta pasut
(Tidal Constant/Form-zahl)
yang dihitung dengan
menggunakan metode
Admiralti yang merupakan
perbandingan jumlah
amplitudo komponen diurnal
terhadap amplitudo
komponen semidiurnal, yang
dinyatakan dengan :
Tabel 1. Pengelompokan Tipe Pasut
AK1 + AO1
F =
AM2 + AS2

Variations in tidal form world wide
'

NIXED TIDE
PREVAIL/NO SENIDIIJRNAL
,.
NIXED TIDE
PREVAIL/NO SENIOIIJ
HIXED TIDE
PREVAILING SENIOIIJRNAL

Komponen Harmonik dari Gaya
Pembangkit Pasut
• Gaya Pembangkit Pasut atau Pasut Ekuilibria
dapat diuraikan menjadi sekumpulan
komponen harmonik atau partial tides
Masing-masing komponen mempunyai:
– amplitudo komponen harmonik yang ditentukan
dari pasut ekuilibria
– periode komponen harmonik yang berkaitan
dengan periode dari edaran (revolusi) chandra,
bumi, dan surya
•

Komponen Harmonik dari Gaya
Pembangkit Pasut (2)
• Komponen harmonik pasut utama adalah
jenis ganda (semi-diurnal) dan tunggal
(diurnal)
Seperti yang telah disebutkankan sebelumnya,
disuatu lokasi dengan koordinat (, ) dapat
dinyatakan sebagai perjumlahan dari fungsi-
fungsi cosinus
•

Komponen Harmonik Utama Pasut
Astronomis
• Komponen M2, mewakili gaya pasut dari Chandra jika
berevolusi di bidang ekuator, dengan kecepatan rerata
dari edaran Chandra
Komponen S2, mirip seperti M2, tetapi untuk Surya
Komponen K1, mewakili efek dari perubahan deklinasi
Chandra dan Surya
Komponen N2, mewakili efek dari revolusi Chandra
yang berbentuk ellips
•
•
•

Tabel 2. Komponen/Konstanta Harmonik Pasut Utama
JENIS NAMA
KOMPONEN
PERIODA (jam) FENOMENA
Semidiurnal M2 12.24 Gravitasi bulan dengan orbit lingkaran dan sejajr ekuator bumi
S2 12.00 Gravitasi matahari dengan orbit lingkaran dan sejajr ekuator
bumi
N2 12.66 Perubahan jarak bulan ke bumi akibat lintasan yang berbentuk
elips
K2 11.97 Perubahan jarak bulan ke bumi akibat lintasan yang berbentuk
elips
Diurnal K1 23.93 Deklinasi sistem bulan dan matahari
O1 25.82 Deklinasi bulan
P1 24.07 Deklinasi matahari
Perioda panjang Mf 327.86 Variasi setengah bulanan
Mm 661.30 Variasi bulanan
Ssa 2191.43 Variasi semi tahunan
Perairan dangkal 2SM2 11.61 Interaksi bulan dan matahari
MNS2 13.13 Interaksi bulan dan matahari dgn perubahan jarak matahari
akibat lintasan berbentuk elips
MK3 8.18 Interaksi bulan dan matahari dgn perubahan jarak bulani akibat
lintasan berbentuk elips
M4 6.21 2 x kecepatan sudut M2
MS4 2.20 Interaksi M2 dan S2

Datum Referensi / Datum Vertikal
Duduk Tengah (DT) / Mean Sea Level (MSL)
adalah permukaan laut rata-rata yang merupakan suatu kedudukan yang
ditentukan melalui pengamatan air laut (pengamatan pasut) untuk
setiap jam, hari, bulan atau tahun.


Dalam survey hidrografi dikenal dua istilah DT, yaitu :
DT Harian pada umumnya ditentukan melalui pengamatan permukaan
laut setiap jam selama satu hari (dari jam 00.00 sampai dengan jam
23.00), sehingga diperoleh 24 harga hasil pengamatan.
DT Bulanan ditentukan melalui nilai rata-rata dari DT Harian untuk waktu
satu bulan. DT Bulanan ini tidak memiliki masa perubahan yang pendek
seperti DT Harian di mana hampir memperlihatkan perubahan yang
merata.
DT Tahunan ditentukan melalui nilai rata-rata dari DT Bulanan untuk
waktu satu tahun (12 bulan).
DT Sejati, merupakan muka laut rata-rata ideal yang tidak lagi
dipengaruhi oleh keadaan pasang surut, di mana pengamatan
kedudukan permukaan laut haruslah dilakukan paling sedikit selama
18,6 tahun. (Djaja, 1979)

 Perhitungan DT dapat dihitung dengan beberapa cara sesuai
dengan periode :
-
-
-
Perhitungan
Perhitungan
Perhitungan
periode
periode
periode
jangka pendek selama satu hari
satu bulan
berbulan-bulan untuk mencari
(mendapatkan) Z0 yang tepat
- Perhitungan periode bertahun-tahun untuk mengetahui
perubahan dari tahun ke tahun dan perubahan periode
jangka panjang. (Sitepu dalam Teknologi Survei Laut, 1996)
 Selain itu nilai DT dapat diperoleh dari hasil analisa harmonik
dengan metode admiralty (konstanta S0).

DT/MSL Harian dengan Perhitungan Jangka Pendek
Nilai DT /Mean Sea Level (MSL) : 69.76 = 70 cm
TinggiMukaAir(cm)
18.00
19.00
20.00
21.00
22.00
23.00
24.00
01.00
02.00
03.00
04.00
05.00
06.00
07.00
08.00
09.00
10.00
11.00
12.00
13.00
14.00
15.00
16.00
17.00
18.00
Grafik Pasang Surut Perairan Tanjung Bayam,
Kec. Tamalate, Kota Makassar
100
90
80
70
60
50 Grafik Tinggi
40 Air (cm)
30
20
10
0
Jam Pengamatan

 Muka Surutan atau Chart Datum (Zo)
adalah bidang yang terletak di bawah air rendah terendah rata-
rata surut, diukur sebesar nilai muka surutan dari DT selama
penelitian atau nilai muka surutan yang telah mengalami koreksi
musim dari DT sejati.
Perhitungan nilai muka surutan dapat dilakukan dengan
menggunakan berbagai formula, yaitu :
Defenisi dari Prancis (Lowest Predicted Low Water),
Zo = 1,2 (M2 + S2 + K2)
Defenisi
Defenisi
Defenisi
Admiralty Inggris, Zo = 1,1 (M2 + S2)
dari Pantai Timur Amerika (Mean Low Water), Z0
dari Australia (Indian Low Water Spring),
= M2
Zo = AM2 + AS2 + AK1 + AO1
( Mihardja, 1987 dalam Ongkosongo dan Suyarso, 1989 dan
Sitepu dalam Teknologi Survei Laut, 1996).

 Air Tinggi Tertinggi (ATT)
Datum pasut lain yang biasa dipakai untuk keperluan
hidrografi adalah air tinggi tertinggi, biasa disebut sebagai
datum elevasi yang didefenisikan menurut persamaan di
bawah ini :
N
S0 +  Ai
i=1
Amplitudo komponen yang dipergunakan dalam persamaan
tersebut adalah amplitudo komponen dari M2, S2, K1, dan O1.
(Mihardja dan Setiadi dalam Ongkosongo dan Suyarso, 1989)

003 008-ocean motions

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