Oceanic currents

Oceanic Currents
Submitted To: Sir. Salman Tariq
Atiqa Ijaz Khan Jan_2013 Weather Forecasting
Semester 7th
Session: 2009-2013
Department of Space Sciences
University of the Punjab

Ocean Currents by Atiqa Page 1
Chapter 1 Welcome to Oceanic Currents 02
Tidal Currents 02
Waves Currents 03
Long-shore Currents 04
Rip Currents 04
Upwelling Currents 05
The Coriolis Force 06
The Ekman Spiral 07
Thermo-haline Movement 07
The Global Conveyer Belt 08
Oceanic Gyres 11
Types of Oceanic Currents 12
Chapter 2 Overview of El Nino and La Nina 14
El Nino 15
La Nina 17
Cold and Warm Episodes by Seasons 18
Chapter 3 References 22

Welcome to Currents
When used in association with water, the term "current" describes the motion of the water.
Some currents you may be familiar with are the motion of rainwater as it flows down the
street, or the motion of the water in a creek, stream, or river flowing from higher elevation
to lower elevation. This motion is caused by gravity. The speed and direction (velocity) of
currents can be measured and recorded.
Tidal currents
They occur in conjunction with the rise and fall of the tide. The vertical motion of the tides
near the shore causes the water to move horizontally, creating currents. When a tidal
current moves toward the land and away from the sea, it “floods.” When it moves toward
the sea away from the land, it “ebbs.” These tidal currents that ebb and flood in opposite
directions are called “rectilinear” or “reversing” currents.
Tidal currents are the only type of current affected by the interactions of the Earth, sun,
and moon. The moon’s force is much greater than that of the sun because it is 389 times
closer to the Earth than the sun is. Tidal currents, just like tides, are affected by the different
phases of the moon. When the moon is at full or new phases, tidal current velocities are
strong and are called “spring currents.” When the moon is at first or third quarter phases,
tidal current velocities are weak and are called “neap currents.”

Waves
Coastal currents are intricately tied to winds, waves, and land formations. Winds that
blow along the shoreline—long shore winds—affect waves and, therefore, currents.

Long-shore Currents
The speed at which waves approach the shore depends on sea floor and shoreline
features and the depth of the water. As a wave moves toward the beach, different
segments of the wave encounter the beach before others, which slows these segments
down. As a result, the wave tends to bend and conform to the general shape of the
coastline. Also, waves do not typically reach the beach perfectly parallel to the
shoreline. Rather, they arrive at a slight angle, called the “angle of wave approach.”
Long-shore currents are generated when a "train" of waves reach the coastline and release
bursts of energy.
Rip Currents
As long-shore currents move on and off the beach,
“rip currents” may form around low spots or breaks
in sandbars, and also near structures such as jetties
and piers. A rip current, sometimes incorrectly called
a rip tide, is a localized current that flows away from

the shoreline toward the ocean, perpendicular or at an acute angle to the shoreline. It
usually breaks up not far from shore and is generally not more than 25 meters (80 feet)
wide.
Upwelling
Winds blowing across the ocean surface often push water away from an area. When this
occurs, water rises up from beneath the surface to replace the diverging surface water.
This process is known as “upwelling.”

The Coriolis Effect
Coastal currents are affected by local winds. Surface ocean currents, which occur on the
open ocean, are driven by a complex global wind system. To understand the effects of
winds on ocean currents, one first needs to understand the Coriolis force and the Ekman
spiral.
If the Earth did not rotate on its axis, the atmosphere would only circulate between the
poles and the equator in a simple back-and-forth pattern. Because the Earth rotates on its
axis, circulating air is deflected toward the right in the Northern Hemisphere and toward
the left in the Southern Hemisphere.
This deflection is called the Coriolis Effect.

The Ekman Spiral
The Ekman spiral, named after Swedish scientist Vagn Walfrid Ekman (1874-1954) who first
theorized it in 1902, is a consequence of the Coriolis Effect. When surface water molecules
move by the force of the wind, they, in turn, drag deeper layers of water molecules below
them. Each layer of water molecules is moved by friction from the shallower layer, and
each deeper layer moves more slowly than the layer above it, until the movement ceases
at a depth of about 100 meters (330 feet). Like the surface water, however, the deeper
water is deflected by the Coriolis Effect—to the right in the Northern Hemisphere and to
the left in the Southern Hemisphere. As a result, each successively deeper layer of water
moves more slowly to the right or left, creating a spiral effect. Because the deeper layers
of water move more slowly than the shallower layers, they tend to “twist around” and
flow opposite to the surface current.
Thermo-haline circulation
Winds drive ocean currents in the upper 100 meters of the ocean’s surface. However, ocean
currents also flow thousands of meters below the surface. These deep-ocean currents are
driven by differences in the water’s density, which is controlled by temperature (thermo)
and salinity (haline). This process is known as thermo-haline circulation.

Global Conveyor Belt
Thermo-haline circulation drives a global-scale system of currents called the “global
conveyor belt.” The conveyor belt begins on the surface of the ocean near the pole in the
North Atlantic. Here, the water is chilled by arctic temperatures. It also gets saltier because
when sea ice forms, the salt does not freeze and is left behind in the surrounding water.
The cold water is now denser, due to the added salts, and sinks toward the ocean bottom.
Surface water moves in to replace the sinking water, thus creating a current.
This deep water moves south, between the continents, past the equator, and down to the
ends of Africa and South America. The current travels around the edge of Antarctica, where
the water cools and sinks again, as it does in the North Atlantic. Thus, the conveyor belt
gets "recharged." As it moves around Antarctica, two sections split off the conveyor and
turn northward. One section moves into the Indian Ocean, the other into the Pacific
Ocean.
These two sections that split off warm up and become less dense as they travel northward
toward the equator, so that they rise to the surface (upwelling). They then loop back
southward and westward to the South Atlantic, eventually returning to the North Atlantic,
where the cycle begins again.
The conveyor belt moves at much slower speeds (a few centimeters per second) than wind-
driven or tidal currents (tens to hundreds of centimeters per second). It is estimated that
any given cubic meter of water takes about 1,000 years to complete the journey along the
global conveyor belt. In addition, the conveyor moves an immense volume of water—
more than 100 times the flow of the Amazon River (Ross, 1995).
The conveyor belt is also a vital component of the global ocean nutrient and carbon
dioxide cycles. Warm surface waters are depleted of nutrients and carbon dioxide, but they
are enriched again as they travel through the conveyor belt as deep or bottom layers. The

base of the world’s food chain depends on the cool, nutrient-rich waters that support the
growth of algae and seaweed.
Cold, salty, dense water sinks at the Earth's northern polar region and heads south along the western Atlantic
basin.
The current is "recharged" as it travels along the coast of Antarctica and picks up more cold, salty, dense
water.
The main current splits into two sections, one traveling northward into the Indian Ocean, while the other
heads up into the western Pacific.

The two branches of the current warm and rise as they travel northward, then loop back around
southward and westward.
The now-warmed surface waters continue circulating around the globe. They eventually return to the
North Atlantic where the cycle begins again.
Oceanic Gyres
Gyres are usually bounded by the shallow waters of continental shelves. There are five
major gyres in the world's oceans, which are delimited by the continents around them.

These gyres are responsible for much of the world's surface currents. As you can see in the
map above, much of the eastern coast of Africa has a current going from north to south,
part of the Indian Ocean Gyre. This current was a great problem to early European
navigators, trying to go around the Cape of Good Hope (the southern tip of Africa) to
find a trade route to India. Early sailing ships tended to hug the coast, where the currents
are strongest, and they didn't have a lot of motive power in the days of sail. Even today,
ships use these currents to save fuel, since making way against the current is costly. Debris
floating in the ocean also tends to converge in certain zones because of these currents. The
North Atlantic Garbage Patch and the Great Pacific Garbage Patch are places where a lot
of trash dumped into the oceans has aggregated.
Types of Ocean Currents
The ocean currents may be classified based on their depth as surface currents and deep
water currents:
(i) Surface currents constitute about 10 per cent of all the water in the ocean, these
waters are the upper 400 m of the ocean;
(ii) Deep water currents make up the other 90 per cent of the ocean water. These
waters move around the ocean basins due to variations in the density and gravity. Deep
waters sink into the deep ocean basins at high latitudes, where the temperatures are cold
enough to cause the density to increase.
Ocean currents can also be classified based on temperature:
(i) Cold currents bring cold water into warm water areas. These currents are usually
found on the west coast of the continents in the low and middle latitudes (true in
both hemispheres) and on the east coast in the higher latitudes in the Northern
Hemisphere;

(ii) Warm currents bring warm water into cold water areas and are usually observed
on the east coast of continents in the low and middle latitudes (true in both
hemispheres). In the northern hemisphere they are found on the west coasts of
continents in high latitudes.
Overview of El Niño and La Niña
El Niño and La Niña are complex weather patterns resulting from variations in ocean
temperatures in the Equatorial Pacific.
El Niño, warmer than average waters in the Eastern equatorial Pacific (shown in orange on the map),
affects weather around the world.
El Niño and La Niña are opposite phases of what is known as the El Niño-Southern
Oscillation (ENSO) cycle. The ENSO cycle is a scientific term that describes the fluctuations
in temperature between the ocean and atmosphere in the east-central Equatorial
Pacific (approximately between the International Date Line and 120 degrees West).

La Niña is sometimes referred to as the cold phase of ENSO and El Niño as the warm
phase of ENSO. These deviations from normal surface temperatures can have large-scale
impacts not only on ocean processes, but also on global weather and climate.
El Niño and La Niña episodes typically last nine to 12 months, but some prolonged events
may last for years. They often begin to form between June and August, reach peak strength
between December and April, and then decay between May and July of the following
year. While their periodicity can be quite irregular, El Niño and La Niña events occur about
every three to five years. Typically, El Niño occurs more frequently than La Niña.
La Niña (December 2000) El Niño (December 1997)
Sea surface temperature anomalies (°C)
El Niño
El Niño means The Little Boy, or Christ Child in Spanish. El Niño was originally
recognized by fishermen off the coast of South America in the 1600s, with the appearance
of unusually warm water in the Pacific Ocean. The name was chosen based on the time of
year (around December) during which these warm waters events tended to occur.
The term El Niño refers to the large-scale ocean-atmosphere climate interaction linked to
a periodic warming in sea surface temperatures across the central and east-central
Equatorial Pacific.

Typical El Niño effects are likely to develop over North America during the upcoming
winter season. Those include warmer-than-average temperatures over western and central
Canada, and over the western and
northern United States. Wetter-than-
average conditions are likely over
portions of the U.S. Gulf Coast and
Florida, while drier- than-average
conditions can be expected in the
Ohio Valley and the Pacific Northwest.

La Niña
La Niña means The Little Girl in Spanish. La Niña is also sometimes called El Viejo, anti-
El Niño, or simply "a cold event."
La Niña episodes represent periods of below-average sea surface temperatures across the
east-central Equatorial Pacific. Global climate La Niña impacts tend to be opposite those
of El Niño impacts. In the tropics, ocean temperature variations in La Niña also tend to be
opposite those of El Niño.
During a La Niña year, winter temperatures are warmer than normal in the Southeast and
cooler than normal in the Northwest.

Notice: Because of the high frequency filter applied to the ERSSTv3b data
(Smith et al. 2008, J.Climate), ONI values may change up to two months after
the initial "real time" value is posted. Therefore, the most recent ONI values
should be considered an estimate.
DESCRIPTION: Warm (red) and cold (blue) episodes based on a threshold of
+/- 0.5oC for the Oceanic Niño Index (ONI) [3 month running mean of
ERSST.v3b SST anomalies in the Niño 3.4 region (5oN-5oS, 120o-170oW)], based
on centered 30-year base periods updated every 5 years. For historical purposes
cold and warm episodes (blue and red colored numbers) are defined when the
threshold is met for a minimum of 5 consecutive over-lapping seasons.
Year DJF JFM FMA MAM AMJ MJJ JJA JAS ASO SON OND NDJ
1950 -1.4 -1.3 -1.2 -1.2 -1.1 -
0.9
-
0.6
-
0.5
-0.4 -0.5 -0.6 -0.7
1951 -
0.8
-0.6 -0.4 -0.2 0.0 0.4 0.6 1.0 1.1 1.2 1.1 0.9
1952 0.6 0.4 0.3 0.3 0.3 0.1 -
0.1
0.0 0.2 0.2 0.2 0.3
1953 0.5 0.6 0.6 0.7 0.7 0.7 0.7 0.7 0.8 0.8 0.8 0.8
1954 0.7 0.5 0.1 -0.4 -0.5 -
0.5
-
0.6
-
0.7
-0.8 -0.7 -0.7 -0.7
1955 -
0.7
-0.7 -0.7 -0.8 -0.8 -
0.8
-
0.8
-
0.7
-1.1 -1.4 -1.7 -1.6

1956 -1.1 -0.8 -0.6 -0.5 -0.5 -
0.5
-
0.5
-
0.6
-0.5 -0.5 -0.5 -0.5
1957 -
0.3
0.1 0.4 0.7 0.9 1.0 1.1 1.2 1.2 1.3 1.5 1.8
1958 1.8 1.6 1.2 0.9 0.7 0.6 0.5 0.3 0.3 0.4 0.5 0.6
1959 0.6 0.6 0.5 0.3 0.2 -0.1 -
0.2
-
0.3
-0.1 0.0 0.1 0.0
1960 -0.1 -0.2 -0.2 -0.1 -0.1 0.0 0.1 0.2 0.2 0.1 0.1 0.1
1961 0.0 0.0 0.0 0.1 0.3 0.4 0.2 -
0.1
-0.3 -0.3 -0.2 -0.1
1962 -
0.2
-0.3 -0.3 -0.3 -0.2 -
0.2
0.0 -
0.1
-0.2 -0.3 -0.4 -0.5
1963 -
0.4
-0.2 0.1 0.3 0.3 0.5 0.8 1.1 1.2 1.3 1.4 1.3
1964 1.1 0.6 0.1 -0.4 -0.6 -
0.6
-
0.6
-
0.7
-0.8 -0.8 -0.8 -0.8
1965 -
0.6
-0.3 0.0 0.2 0.5 0.8 1.2 1.5 1.7 1.9 1.9 1.7
1966 1.4 1.1 0.9 0.6 0.4 0.3 0.3 0.1 0.0 -0.1 -0.1 -0.2
1967 -
0.3
-0.4 -0.5 -0.4 -0.2 0.1 0.1 -
0.1
-0.3 -0.3 -0.3 -0.4
1968 -
0.6
-0.8 -0.7 -0.5 -0.2 0.1 0.4 0.5 0.5 0.6 0.8 1.0
1969 1.1 1.1 1.0 0.9 0.8 0.6 0.5 0.5 0.8 0.9 0.9 0.8
1970 0.6 0.4 0.4 0.3 0.1 -
0.2
-
0.5
-
0.7
-0.7 -0.7 -0.8 -1.0

1971 -1.2 -1.3 -1.1 -0.8 -0.7 -
0.7
-
0.7
-
0.7
-0.7 -0.8 -0.9 -0.8
1972 -
0.6
-0.3 0.1 0.4 0.6 0.8 1.1 1.4 1.6 1.9 2.1 2.1
1973 1.8 1.2 0.6 -0.1 -0.5 -
0.8
-
1.0
-
1.2
-1.3 -1.6 -1.9 -2.0
1974 -1.9 -1.6 -1.2 -1.0 -0.8 -
0.7
-
0.5
-
0.4
-0.4 -0.6 -0.8 -0.7
1975 -
0.5
-0.5 -0.6 -0.7 -0.8 -1.0 -1.1 -
1.2
-1.4 -1.5 -1.6 -1.7
1976 -1.5 -1.1 -0.7 -0.5 -0.3 -0.1 0.2 0.4 0.6 0.7 0.8 0.8
1977 0.6 0.6 0.3 0.3 0.3 0.4 0.4 0.4 0.5 0.7 0.8 0.8
1978 0.7 0.5 0.1 -0.2 -0.3 -
0.3
-
0.3
-
0.4
-0.4 -0.3 -0.1 -0.1
1979 -0.1 0.1 0.2 0.3 0.2 0.0 0.0 0.2 0.3 0.5 0.5 0.6
1980 0.5 0.4 0.3 0.3 0.4 0.4 0.3 0.1 -0.1 0.0 0.0 -0.1
1981 -
0.4
-0.6 -0.5 -0.4 -0.3 -
0.3
-
0.4
-
0.4
-0.3 -0.2 -0.2 -0.1
1982 -0.1 0.0 0.1 0.3 0.5 0.7 0.7 1.0 1.5 1.9 2.1 2.2
1983 2.2 1.9 1.5 1.2 0.9 0.6 0.2 -
0.2
-0.5 -0.8 -0.9 -0.8
1984 -
0.5
-0.3 -0.3 -0.4 -0.5 -
0.5
-
0.3
-
0.2
-0.3 -0.6 -0.9 -1.1
1985 -1.0 -0.9 -0.7 -0.7 -0.7 -
0.6
-
0.5
-
0.5
-0.5 -0.4 -0.4 -0.4

1986 -
0.5
-0.4 -0.2 -0.2 -0.1 0.0 0.3 0.5 0.7 0.9 1.1 1.2
1987 1.2 1.3 1.2 1.1 1.0 1.2 1.4 1.6 1.6 1.5 1.3 1.1
1988 0.8 0.5 0.1 -0.2 -0.8 -1.2 -
1.3
-
1.2
-1.3 -1.6 -1.9 -1.9
1989 -1.7 -1.5 -1.1 -0.8 -0.6 -
0.4
-
0.3
-
0.3
-0.3 -0.3 -0.2 -0.1
1990 0.1 0.2 0.3 0.3 0.2 0.2 0.3 0.3 0.4 0.3 0.4 0.4
1991 0.3 0.2 0.2 0.3 0.5 0.7 0.8 0.7 0.7 0.8 1.2 1.4
1992 1.6 1.5 1.4 1.2 1.0 0.7 0.3 0.0 -0.2 -0.3 -0.2 0.0
1993 0.2 0.3 0.5 0.6 0.6 0.5 0.3 0.2 0.2 0.2 0.1 0.1
1994 0.1 0.1 0.2 0.3 0.4 0.4 0.4 0.4 0.5 0.7 1.0 1.2
1995 1.0 0.8 0.6 0.3 0.2 0.0 -
0.2
-
0.4
-0.7 -0.8 -0.9 -0.9
1996 -
0.9
-0.8 -0.6 -0.4 -0.3 -
0.2
-
0.2
-
0.3
-0.3 -0.3 -0.4 -0.5
1997 -
0.5
-0.4 -0.1 0.2 0.7 1.2 1.5 1.8 2.1 2.3 2.4 2.3
1998 2.2 1.8 1.4 0.9 0.4 -
0.2
-
0.7
-
1.0
-1.2 -1.3 -1.4 -1.5
1999 -1.5 -1.3 -1.0 -0.9 -0.9 -1.0 -
1.0
-1.1 -1.1 -1.3 -1.5 -1.7
2000 -1.7 -1.5 -1.2 -0.9 -0.8 -
0.7
-
0.6
-
0.5
-0.6 -0.6 -0.8 -0.8
2001 -
0.7
-0.6 -0.5 -0.4 -0.2 -0.1 0.0 0.0 -0.1 -0.2 -0.3 -0.3

2002 -
0.2
0.0 0.1 0.3 0.5 0.7 0.8 0.8 0.9 1.2 1.3 1.3
2003 1.1 0.8 0.4 0.0 -0.2 -0.1 0.2 0.4 0.4 0.4 0.4 0.3
2004 0.3 0.2 0.1 0.1 0.2 0.3 0.5 0.7 0.8 0.7 0.7 0.7
2005 0.6 0.4 0.3 0.3 0.3 0.3 0.2 0.1 0.0 -0.2 -0.5 -0.8
2006 -
0.9
-0.7 -0.5 -0.3 0.0 0.1 0.2 0.3 0.5 0.8 1.0 1.0
2007 0.7 0.3 -0.1 -0.2 -0.3 -
0.3
-
0.4
-
0.6
-0.8 -1.1 -1.2 -1.4
2008 -1.5 -1.5 -1.2 -0.9 -0.7 -
0.5
-
0.3
-
0.2
-0.1 -0.2 -0.5 -0.7
2009 -
0.8
-0.7 -0.5 -0.2 0.2 0.4 0.5 0.6 0.8 1.1 1.4 1.6
2010 1.6 1.3 1.0 0.6 0.1 -
0.4
-
0.9
-
1.2
-1.4 -1.5 -1.5 -1.5
2011 -1.4 -1.2 -0.9 -0.6 -0.3 -
0.2
-
0.2
-
0.4
-0.6 -0.8 -1.0 -1.0
2012 -
0.9
-0.6 -0.5 -0.3 -0.2 0.0 0.1 0.4 0.5 0.6 0.2 -0.3
2013 -
0.6
-0.6 -0.4 -0.2 -0.2 -
0.3
-
0.3
-
0.3
-0.3 -0.2 -0.3 -0.4
2014 -
0.6
-0.6 -0.5 -0.2

References:
 http://oceanservice.noaa.gov/education/kits/currents/lessons/currents_tutorial.pdf
 http://oceanservice.noaa.gov/facts/ninonina.html
 http://earthobservatory.nasa.gov/Features/LaNina/
 http://kids.earth.nasa.gov/archive/nino/intro.html
 http://www.elnino.noaa.gov/lanina.html
 http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml

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