Transcript ocean_10_lecture_5

Water’s Thermal Properties
• Water is solid, liquid, and gas at Earth’s surface.
• Water influences Earth’s heat budget.
Water’s Three States of Matter
Latent Heat of Vaporization = 600 calories / 1g
Latent Heat of Condensation = 600 calories / 1g
Latent Heat of Fusion= 80 calories / 1g
How much energy to sublimate?
http://www2.chemistry.msu.edu/courses/cem152/snl_cem152_SS12/pracprob/practiceexam1.html
Surface Salinity Variation by Latitude
Temperature and Density Variation With
Depth
• Pycnocline – abrupt change of density with depth
• Thermocline – abrupt change of temperature with
depth
CHAPTER 6
Air-Sea Interaction
• The atmosphere and the ocean are coupled in many
ways.
• Earth has seasons because of the tilt on its axis.
• There are three major wind belts in each hemisphere.
• The Coriolis effect influences atmosphere and ocean
behavior.
• Oceanic climate patterns are related to solar energy
distribution.
Heat Gained and Lost
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Density Variations in the Atmosphere
• Convection cell – rising
and sinking air
• Warm air rises
– Less dense
• Cool air sinks
– More dense
• Moist air rises
– Less dense
• Dry air sinks
– More dense
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Movement of the Atmosphere
• Air always flows from high to low pressure.
• Wind – moving air
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Coriolis Force varies with latitude:
Movements in the Air
• Example: a nonrotating Earth
• Air rises at equator (low
pressure)
• Air sinks at poles (high
pressure)
• Air flows from high to
low pressure
• One convection cell or
circulation cell
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Global Atmospheric Circulation
• Circulation Cells – one in each hemisphere
– Hadley Cell: 0–30 degrees latitude
– Ferrel Cell: 30–60 degrees latitude
– Polar Cell: 60–90 degrees latitude
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Global Atmospheric Circulation
• High pressure zones – descending air
– Subtropical highs – 30 degrees latitude
– Polar highs –90 degrees latitude
– Clear skies
• Low pressure zones – rising air
– Equatorial low – equator
– Subpolar lows – 60 degrees latitude
– Overcast skies with lots of precipitation
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• Circulation Cells –
one in each
hemisphere
– Polar Cell: 60–90
degrees latitude
– Ferrel Cell: 30–60
degrees latitude
– Hadley Cell: 0–30
degrees latitude
Winds
• Cyclonic flow
– Counterclockwise around a
low in Northern
Hemisphere
– Clockwise around a low in
Southern Hemisphere
• Anticyclonic flow
– Clockwise around a low in
Northern Hemisphere
– Counterclockwise around a
low in Southern
Hemisphere
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Winds and related forces around areas of low and high pressure above
the friction level in the Northern Hemisphere. Notice that the pressure
gradient force (PGF) is in red, while the Coriolis force (CF) is in blue.
Fronts
• Fronts – boundaries
between air masses
– Warm front
– Cold front
• Storms typically
develop at fronts.
• Jet Stream – may cause
unusual weather by
steering air masses.
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CHAPTER 7
Ocean Circulation
Ekman Spiral
• Surface currents move at
an angle to the wind.
• The Ekman spiral
describes speed and
direction of seawater flow
at different depths.
• Each successive layer
moves increasingly to the
right in the Northern
Hemisphere
– Coriolis effect
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Ekman Transport
• Average movement of
seawater under
influence of wind
• 90 degrees to right of
wind in Northern
hemisphere
• 90 degrees to left of
wind in Southern
hemisphere
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Geostrophic Flow
• Ekman transport piles up
water within subtropical
gyres.
• Surface water flows
downhill and to the
right.
• Geostrophic flow –
balance of Coriolis Effect
and gravitational forces
• Ideal geostrophic flow
• Friction generates actual
geostrophic flow
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Coastal Upwelling
• Ekman transport moves
surface seawater
offshore.
• Cool, nutrient-rich deep
water comes
up to replace displaced
surface waters.
• Example: U.S.
West Coast
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Coastal Downwelling
• Ekman transport moves
surface seawater
toward shore.
• Water piles up, moves
downward in water
column
• Lack of marine life
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Atmospheric-Ocean Connections in the
Pacific Ocean
• Walker Circulation Cell – normal conditions
– Air pressure across equatorial Pacific is higher in
eastern Pacific
– Strong southeast trade winds
– Pacific warm pool on western side of ocean
– Thermocline deeper on western side
– Upwelling off the coast of Peru
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Normal Conditions, Walker Circulation
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El Niño – Southern Oscillation (ENSO)
Walker Cell Circulation disrupted
• High pressure in eastern Pacific weakens
• Weaker trade winds
• Warm pool migrates eastward
• Thermocline deeper in eastern Pacific
• Downwelling
• Lower biological productivity
– Peruvian fishing suffers
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ENSO Conditions in the Pacific Ocean
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La Niña – ENSO Cool Phase
• Increased pressure difference across
equatorial Pacific
• Stronger trade winds
• Stronger upwelling in eastern Pacific
• Shallower thermocline
• Cooler than normal seawater
• Higher biological productivity
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La Niña Conditions
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Occurrence of ENSO Events
• El Niño warm phase about every
2–10 years
• Highly irregular
• Phases usually last 12–18 months
• 10,000-year sediment record of events
• ENSO may be part of Pacific Decadal
Oscillation (PDO)
– Long-term natural climate cycle
– Lasts 20–30 years
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Thermohaline Circulation
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http://en.wikipedia.org/wiki/Thermohaline_circulation
The term thermohaline circulation (THC) refers to a part of the large-scale ocean circulation that is driven by
global density gradients created by surface heat and freshwater fluxes. The adjective thermohaline derives
from thermo- referring to temperature and -haline referring to salt content, factors which together
determine the density of sea water. Wind-driven surface currents (such as the Gulf Stream) travel polewards
from the equatorial Atlantic Ocean, cooling enroute, and eventually sinking at high latitudes (forming North
Atlantic Deep Water). This dense water then flows into the ocean basins . While the bulk of it upwells in the
Southern Ocean, the oldest waters (with a transit time of around 1600 years) upwell in the North Pacific.
Extensive mixing therefore
takes place between the
ocean basins, reducing
differences between them
and making the Earth's
oceans a global system. On
their journey, the water
masses transport both
energy (in the form of heat)
and matter (solids, dissolved
substances and gases)
around the globe. As such,
the state of the circulation
has a large impact on the
climate of the Earth.
http://www.tsc.upc.edu/rslab/Passive%20Remote%20Sensing/activities/sea%20surface%20salinity
http://www.nc-climate.ncsu.edu/edu/water/water.oceancirculations