Transcript Slide 1

Weather & Circulation
The ocean and its currents have a major influence
on weather and climate on Earth.
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Atmosphere
• Air composed mostly of nitrogen and oxygen
– Never dry – always contains water vapor
– Air’s density determined by
• Temperature
• Water content
• Weather - The state of the atmosphere at a given time and place,
with respect to variables such as temperature, moisture, wind
velocity, and barometric pressure.
• Climate - The meteorological conditions, including temperature,
precipitation, and wind, that characteristically prevail in a particular
region.
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Greenhouse Effect
• Greenhouse effect - The atmosphere of
our Earth traps heat
– the energy from the sun also heats up
the oceans.
• 50% of radiation from the sun is
absorbed by the Earth’s surface and
then reflected back into the earth’s
atmosphere.
– Gases (carbon dioxide and water
vapor) can stop this energy from
escaping into space by keeping it here
on Earth.
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Global Warming
• Scientists have noticed that the Earth is
experiencing a warming trend.
• In the past 100 years, the Earth’s mean
global temperature has increased more
than 1 degree Farenheit and ocean
levels have risen
• Global warming is the result, the
gradual increase in Earth’s
temperature.
• Scientists measure polar ice caps to
determine if their rate of melting
continues to increase.
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Measuring the Melt
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The graph below shows total ice coverage since 1973.
As glacial ice melts, sea levels rise and ocean currents can change.
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Average temperatures in the Arctic region are rising twice as fast as they are elsewhere in the
world. Arctic ice is getting thinner, melting and rupturing.
– the largest single block of ice in the Arctic, the Ward Hunt Ice Shelf, had been around for
3,000 years before it started cracking in 2000. Within two years it had split all the way
through and is now breaking into pieces.
The polar ice cap as a whole is shrinking.
– Images from NASA satellites show that the area of permanent ice cover is contracting
at a rate of 9 percent each decade.
– If this trend continues, summers in the Arctic could become ice-free by the end of the
century.
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The melting of once-permanent ice is already affecting native people, wildlife and plants.
– When the Ward Hunt Ice Shelf splintered, the rare freshwater lake it enclosed, along
with its unique ecosystem, drained into the ocean.
– Polar bears, whales, walrus and seals are changing their feeding and migration
patterns, making it harder for native people to hunt them.
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Carbon Dioxide levels
• The amount of carbon dioxide in the atmosphere has been steadily
increasing.
• As we continue to cut down trees for paper production, we are
decreasing the plants that convert CO2 to oxygen, causing an increase
in CO2 levels.
• The burning of fossil fuels (oil, coal, etc) also adds carbon dioxide to the
environment.
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Natural Air Pollution
• Even “clean” air is not
perfectly clean.
• It contains many pollutants
from natural sources like dust,
volcanic gases and ash,
smoke from forest fires,
pollen, etc.
• Most of the air pollution
mentioned in the news is a
result of human activities.
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Natural Cycle?
• natural phenomenon - climate has gone through periods of warmth
and periods of extreme cold (often known as an Ice Age).
• Some scientists claim that the warming trend is part of a natural
cycle that will eventually reverse itself through CO2 uptake by
photosynthetic marine and terrestrial plant life.
• Others claim that the warming of Earth’s atmosphere is a real
problem that can be reduced by decreasing the use of fossil fuels
and finding alternative energy sources.
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Currents
• Ocean currents - moving water connecting major
landmasses on Earth
– global ocean currents – largest currents that move
across the ocean (like rivers that travel great distances)
– affected by
• global temperature
• freshwater glacial ice melt
• density differences due to salt concentrations and
temperature differences.
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Water’s Density
• Density is important to the currents which shape the
planet’s climate.
– Fresh water is less dense than salty water.
– Warm water has a lower density than cold water
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Effect of Salinity
• Salty water will sink while fresh water will rise because of
differences in density.
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In the Mediterranean
• The Mediterranean Sea, for example, has a higher salinity than the
Atlantic Ocean, creating a current south of Spain that moves salty
water deep into the Atlantic Ocean.
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Global Ocean Currents
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Radiant
Energy
• The sun, the source of all energy on Earth, gives off radiant energy and
influences the climate that we experience.
• Angle of Isolation - the angle at which the rays of the sun strike the
surface of the earth.
– Determines the amount of radiant (or solar) energy that reaches any
part of the planet
• Areas farthest away from the sun’s rays (the poles) receive slanted rays
with a larger angle, and are therefore less intense
– Caused by:
• The Earth’s curved surface
• the tilt of its axis
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Ocean Temperature
• The uneven heating of the Earth due to the rays of the sun
causes ocean temperatures to vary with latitude.
• The ocean is warmest at the equator.
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Coriolis Effect
• The coriolis effect - the spinning Earth causes the winds and
surface waters to move in a specific directions.
• northern hemisphere - the
currents deflect clockwise to the
east.
• southern hemisphere - currents
move in the opposite direction,
counter clockwise to the west.
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Gyres
• Gyres - giant circles created when the water moves and hits
the continent which deflect the currents
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Gulf Stream
• The gulf stream current flows from the southwestern
Atlantic to the northeastern
– it is the major factor in favorable (warm) weather on
the eastern coast of the United States.
• Benjamin Franklin was the first to chart the temperature
and speed of the gulf stream back in the 1700s.
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Subsurface Currents
• Subsurface currents - move because of differences in temperature and
salinity.
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Downwelling & Upwelling
• Downwelling - After warm water has risen to the surface, it will
eventually cool off and therefore sink again near the poles
• Upwelling - When currents rise to the surface, they bring nutrient-rich
sediments from the bottom.
• Nutrients found on the floor of the ocean (such as phosphates &
nitrates) are important for all organisms in aquatic food webs.
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Coastal
Currents
• Waves – when currents eventually meet coastal areas
– After a wave breaks on a beach, the forward momentum transports
water up the slope of a beach.
– The returning current or backwash is called the undertow.
• Currents that move parallel to the beach are called longshore currents.
• Spaces between islands off the coast of a continent, like Galveston
and South Padre, cause a rush of water called a rip current that moves
quickly out into the ocean.
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Tidal Currents
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• The movement of the moon around the Earth and it’s gravity causes
tides
– the daily rise and fall of the ocean seen along the shore.
• When a tide enters and leaves and area, the tidal change produces
swift-moving tidal currents that run parallel to the shore.
– important to aquatic food chains because they carry nutrients and
small organisms back and forth between the bays and the
offshore waters.
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Ocean Wind
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Convection currents occur in many different media
(liquid, air, magma).
Day Time
– Often, the wind around the ocean creates a sea
breeze
• due to differences in temperature of the air
over the ocean versus over land.
– Water heats up slowly, while land heats up
quickly.
– A convection current is created because the
cooler air over the ocean sinks and travels
inland while the warm air over the land rises up.
Night Time
– The opposite occurs
– land cools very quickly, but water has a very
high specific heat and takes longer to cool.
– The air over the water is warmer and wind
travels out to the ocean in the reversed
convection current.
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Humidity
• Humidity- amount of water vapor into the atmosphere
– Coastal regions often have a higher level of humidity than inland
areas because they are exposed to the moisture that evaporates from
the ocean.
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Fog & Dew
• Fog - Air saturated with moisture creating
clouds near the ground
– forms when warm, moist air makes
contact with a cold surface.
– The mirror in your bathroom often “fogs”
when warm moist air from the shower
hits the cold surface of the mirror.
• Dew - When water condenses (changes
from a vapor to a liquid) on a solid surface
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Hurricanes
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A hurricane -a coastal storm with a wind velocity exceeding 120 km/hr
Form in warm tropical seas where there is hot, moist air
– As hot, moist air rises, it cools in the upper atmosphere and condenses into
ring shaped clouds.
– During condensation, a great deal of heat energy is released, which
causes more hot air to rise even quicker.
– This whirlwind of rising air moves in a spiral direction around calm air
knows as the “eye” of a hurricane.
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El Nino
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El Nino - Oceanic warming
Begins in the western Pacific Ocean
Warm currents are normally carried northwest due to trade winds.
El Nino reverses the currents because of a decline in southeast trade
winds
• causes a change in the climate of South America (bringing floods
and stormy weather).
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La Nina
• La Nina - Unusually cold currents causing cooler surface
temperatures
• winters are cooler than normal in the northwest United states and
warmer than normal in the southeast.
• The cycles for El Nino/La Nina often last 1 to 2 years and occur
every 4 to 6 years.
• Click on the graphic to view an animation depicting the differences
between El Nino and La Nina.
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