Download Ocean Currents

Ocean Currents
• Ocean Density
Energy in = energy out
Half of solar radiation
reaches Earth
The atmosphere is
transparent to
shortwave but absorbs
longwave radiation
(greenhouse effect)
The atmosphere is
heated from the bottom
by longwave radiation
and convection
Climatic Variation & Seasons on Earth
I. Uneven heating of Earth’s surface causes predictable latitudinal variation
in climate. Why? - Angle of incidence… equator vs. poles
North Pole
Equator
Earth
South Pole
Thus, radiation is more intense near the equator compared to the poles.
For this reason, it’s warmer near the equator than at the poles.
Uneven heating of Earth’s surface causes atmospheric circulation
Greater heating at equator than poles
1. sun’s rays hit more directly
2. less atmosphere to penetrate
Therefore
1. Net gain of energy at equator
2. Net loss of energy at poles
II. What about seasons? Why do we have them?
Earth’s distance from the sun varies throughout the
year – doesn’t that cause the seasons?
Tilt!
Because of the tilt of Earth’s axis, the amount of radiation received by
Northern and Southern Hemispheres varies seasonally
A. Northern Hemisphere has summer when it tilts toward the sun,
winter when it tilts away
B. Southern Hemisphere has summer when it tilts toward the sun,
winter when it tilts away
Earth’s Seasons
I.
Tilt of the Earth’s axis towards or away from the sun creates the seasons
When the north pole tilts toward the
sun, it gets more radiation – more warmth
during the summer
When the north pole tilts toward the
sun, the south pole tilts away
So when it’s summer in the north,
it’s winter in the south
SUMMER (Northern Hemisphere)
WINTER (Southern Hemisphere)
Earth’s Seasons
I.
Tilt of the Earth’s axis towards or away from the sun creates the seasons
When the north pole tilts away
from the sun, it gets less radiation –
So it’s colder during the winter
When the north pole tilts away from the
sun, the south pole tilts toward it…
When it’s winter in the north,
it’s summer in the south
WINTER (Northern Hemisphere)
SUMMER (Southern Hemisphere)
Air rises and falls
in Hadley, Ferrel, and
Polar cells
(vertical circulation)
Circulation cells
explain global
distribution of
rainfall
Earth’s rotation
determines
wind direction
(horizontal circulation,
Coriolis force)
High heat capacity of water and ocean currents buffer
ocean temperatures
Land temperatures fluctuate more, especially in higher
latitudes
These differences in surface energy balance influence air
movements, and create prevailing winds
• Salinity – The difference
in the salinity of hot and
cold water drives the
currents. The higher the
salinity of the water, the
more dense the water is.
• Density - the state or
quality of compactness;
closely set or crowded
condition.
• Water Mass – Area of
different salinity density
in the ocean.
In January…
At 30º N & S, air descends more strongly over cold ocean than over land
At 60 º N & S, air descends more strongly over cold land than over ocean
These pressure gradients create geographic variation in prevailing winds
In summer at 60 º N & S, air descends over cold ocean (high pressure)
and rises over warm land (low pressure)
Cool equator-ward flow of air on W coast of continents
Warm poleward flow of air on E coasts of continents
Ocean currents are similar to wind patterns:
1. Driven by Coriolis forces
2. Driven by winds
Ocean currents move 40% of “excess heat” from equator to poles
Driven by circulation of deep ocean waters
Deepwater formation occurs near Greenland and in Antarctic
60% of heat transport is carried by
atmosphere through storms that
move along pressure gradients
The Pacific Ocean strongly influences the climate system because
It is the largest ocean basin
Normal ocean current and wind direction in central Pacific is easterly
Winds and surface water
• Wind blowing over the ocean can move it due
to frictional drag.
• Waves create necessary roughness for wind to
couple with water.
• One “rule of thumb” holds that wind blowing
for 12 hrs at 100 cm per sec will produce a 2
cm per sec current (about 2% of the wind
speed)
Top-down drag
• Wind acts only on the surface water layer.
• This layer will also drag the underlying water,
but with less force.
• Consequently, there is a diminution of speed
downward.
• Direction of movement is also influenced by
the Coriolis Effect and Ekman Spiral
Geostrophic Flow
Surface currents generally mirror average planetary
atmospheric circulation patterns