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Ocean and Coastal Currents

GD3208-Coastal Environmental Survey

Dr.rer.nat. Wiwin Windupranata

(2)

Objectives

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Ocean Circulation

Why It is Important

• Impact all human activities on

the ocean or in the coastal area

(transportation, fishing,

mariculture, tourism and sport,

erosion and sedimentation,

water pollution, etc)

• Redistribute heat in global

climatic pattern

How is the Movement of Ocean

Waters

• Currents, Tides and Waves



(4)

Driving Factors

In shallow water (coastal

area)

• tides



the most

important

• bottom friction

• bathymetry

• fresh water discharges

from rivers

In deep water (offshore

area)

• winds



surface layer

(5)

Ocean Circulation

Magnitudes of Ocean

Currents

• the magnitude of currents

in units of sverdrups (Sv)

• 1 sv = 1,000,000 m

3/

_s

• the magnitude of the

major ocean currents range

from a few sverdrup to

over 100 sverdrup

(6)

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Atmospheric Processes

Winds flow from higher to lower

atmospheric pressure

• air pressure is the weight of the air

from Earth’s surface to the top of the

atmosphere and equals 1.04kg/cm2

(standard air pressure, one

atmosphere) at sea level

• change in pressure across a horizontal

distance is a pressure gradient

• greater the difference in pressure and

the shorter the distance between

them, the steeper the pressure

(8)

Atmospheric Processes

Global wind pattern is

controlled by the density of

atmosphere

• Density is a function of

temperature, pressure and

moisture content

• Warm air is less dense than

cold air and moist air is less

dense than dry air

• Warm air has less pressure

and cold air has more

pressure

(9)

Atmospheric Processes

Maximum Solar Heating at the

equator (over 400 Watts per

square meter) and minimum

at the poles (less than 200

Watts per square meter)

• At the equator, sunlight strikes

the earth at a nearly

perpendicular angle.

• The atmosphere absorbs a

certain fraction of the sunlight

striking the earth. Sunlight

(10)

Atmospheric Processes

Uneven solar heat

distribution

• Because air at the

equator is warmer than

air at the poles, it is less

dense

(11)

Atmospheric Processes

Uneven solar heat distribution

• three circulation cells form

between the equator and each

pole

• air sinks at both 30° latitude and

the poles; rises at about 60°

latitude, moves north and south

• due to the Coriolis effect, flow on a

sphere curves: to the right in the

northern hemisphere and to the

left in the southern hemisphere.

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Gyre

Western boundary

currents -These are

narrow, deep, fast

currents found at the

western boundaries of

ocean basins

• the Gulf Stream

• the Japan Current

• the Brazil Current

• the Agulhas Current

(16)

Gyre

Eastern boundary

currents

–

These currents

are cold, shallow and

broad, and their

boundaries are not well

defined

• the Canary Current

• the Benguela Current

• the California Current

• the West Australian

Current

(17)

Monsoon

Monsoons are patterns

of wind circulation

that change with the

season

Areas with monsoons

generally have dry

winters and wet

summers

(18)

21 Dec

20 Mar

20 Jun

(19)

(20)

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(22)

(23)

(24)

Upwelling and Downwelling

Wind induced vertical

circulation is vertical movement

induced by wind-driven

horizontal movement of water

• Upwelling is the upward motion

of water. This motion brings cold,

nutrient rich water towards the

surface

(25)

Upwelling and Downwelling

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Upwelling and Downwelling

(27)

Indonesian Throughflow

Very important in world

climates

• Due to difference of Sea Surface

Topography at Pacific and

Indian Oceans

• Global exchange of water and

heat between the Pacific and

Indian Oceans

• Influences the climate conditions

in eastern Indonesia and western

Australia

(28)

Deep Water Currents

In deep water, currents are

mainly driven by differences in

density, which is the function of

salinity, temperature and

depth

• Water at the surface is exposed

to more rapid changes in salinity

through evaporation or

precipitation and in temperature

through cooling or heating

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El Niño

Under Normal Conditions

• Easterly trade winds cause

surface waters to pile up in the

west

• Thermocline is deep in the west

and shallow in the east

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El Niño

El Niño Conditions

• Easterly trade winds are

weakening

• Thermocline is shallower in the

west and deeper in the east

compare to normal condition

• Sea level at western Pacific

drops, upwelling occurs

(32)

El Niño

Under Normal Conditions

• Satellite derived estimates of Sea

Surface Temperature during

normal (1996), El Niño

Conditions (1997), and Sea

(33)

El Niño

(34)

Thank You !!!

Dr.rer.nat. Wiwin Windupranata