Transcript Phys. 102: Introduction to Astronomy

SOAR 2005
Ocean Circulation and Heat
Transport
Coriolis Force: All moving objects are
deflected
to their
right in
northern
hemisphere
to their left
in southern
hemisphere
Coriolis Force
Northern Hemisphere
Southern Hemisphere
Moving objects
deflected to their own
right.
Moving objects
deflected to their own
left.
Tropical Cyclone Olyvia
L
L
Hurricane Isabel
Storms rotate
counterclockwise
Storms rotate
clockwise
Energy Transfer
 Convection – hot stuff moves
 Conduction – hot stuff heats neighbors
 Radiation – heat moves as IR radiation
Properties of Water
 General properties
 Stable (hard to tear apart)
 Versatile solvent (universal solvent)
 Polar properties
 Give rise to surface tension
 Capillary action
 Responds to electric fields
 Solid floats in the liquid
 Ponds freeze on top, ice insulates water!
 Water most dense as liquid at 4C
Heat Properties of Water
High latent heats
 1 calorie = 4.186 Joules
 High Heat Capacity
High energy gain/loss to change temperature
Energy Transfer by Water
 Specific Heat
 Energy absorbed or
released to change temp.
Raising 1 kg of
water 1°C
absorbs 4,168
Joules
1 kg
10 cm
square
cube of
water
Substance
Specific Heat
(Joule/K/kg)
Air (50C)
1050
Iron or Steel
460
Lead
130
Glass
840
Quartz
762
Granite
804
Sandstone
1088
Shale
712
Soil (average)
1050
Wood (average)
1680
Ice
2100
Steam
2050
Water
4168
4000 Joules ≈ energy to lift 400 kg or 900 lb 1 m
Energy Transfer by Water
 Latent Heat
Specific Heat (Joule/kg)
 Energy absorbed or
Substance
released to change phase
vaporization
Evaporating 1 kg
of water
absorbs
2,257,000Joules
1 kg
fusion
Alcohol
879,000
109,000
Water
2,257,000
333,500
10 cm
square
cube of
water
2,257,000 Joules ≈ energy to lift 225,700 kg or 507,000 lb 1 m
Energy Transfer by Water
Latent heat effects weather
Evaporating water
absorbs energy from
water, cooling it.
Condensing water
releases energy to
air, heating it.
Energy Budget
 Insolation
 Sun’s incident energy drives air motions
(energy from deep interior adds a tiny bit)
 Distribution of Sunlight
 Reflection from clouds, landscape
 Absorption by atmosphere
 Absorption by surface
 Albedo = ratio of sunlight reflected
 Earth: 0.367
 Moon: 0.113
 Mars: 0.15
 Venus: 0.84
Insolation: 1,373 W/m2
Most solar energy comes in as
light (shortwave radiation)
30% Reflected by
atmosphere
20% Absorbed by
atmosphere
50% Absorbed by
Earth’s surface
Energy Flow from Surface
7% conducted to air
23% transferred by water
20% radiated
as IR
(longwave)
% of total
insolation
Energy Absorbed by Atmosphere
% of total
insolation
20% from Sun
7% conducted from surface
23% transferred by water
8% radiated by surface
Complete Energy Budget
Temperature Controls
 Sunlight heats land, water, air
 Land warms, heats air
 Air circulates
 Convection cells
 warms -> expands -> rises
 cools -> contracts -> sinks
 Water circulates
 Currents driven by wind & Earth rotation
 Water temperature increases SLOWLY
 Large energy change needed for small temp. change
Atmospheric Circulation
Sunlight heats ground
Ground heats air , drives convection from
subsolar latitude
Subsolar latitude
is 0º on the
equinoxes
Maximum Insolation
Subsolar latitude
is 23.5º N/S on
the solstices
Moist air rising
 stormy
Dry air falling
 Arid
Moist air rising
 stormy
Dry air falling
 Arid
Pressure Zones
Pressure
Zones:
air motion
is vertical
so there is
little wind!
Winds
named
for
direction
they are
from
Windless
zones
names vary
Wind Zones
Easterlies
Polar Front
Westerlies
Horse Latitudes
NE Trades
Doldrums
SE Trades
Horse Latitudes
Westerlies
Polar Front
Easterlies
Oceans’ Impact on Climate
 Most common compound on Earth
 Covers 71% of surface area
 Land area on Earth = surface on Mars
 1.36 billion km3 (326 million mk3)
 70% of us by weight
 Major constituent of most plants & animals
 Originated from
 Outgasing of Volcanos (continues)
 Bombardment by comets (much reduced)
 Present volume established 2 by ago
 Quantity in equilibrium
Location of Water
 Southern Hemisphere
 Moderates climate
Westerlies
Easterlies
 Earth closest to sun in
January (southern summer)
 Antarctica surrounded
 Strong winds, currents
 Isolates Antarctic High
 within “polar vortex”
 Traps CFC’s, Destroys ozone
Pacific Ocean
 Covers ½ the Earth
 Navigated by Polynesians
and Chinese in ancient times?
Mosaic of Antarctica from
Galileo spacecraft
Location of Water
 Oceans 97.22%




Pacific
Atlantic
Indian
Arctic
48%
28%
20%
4%
4280 km
3930
3960
1205
Percentage of freshwater
(14 kft) deep
(13 kft)
(13 kft)
( 4 kft)
Percentage of
surface water
Properties of Water
Present as solid, liquid, gas on Earth
Gas & solid on Mars & most places
Solid and liquid (?) on Europa
Polar molecule H2O
Oxygen
8 p+, 8 no, 8e-
Hydrogen
1 p+, 1 e-
e- tend to hang
around Oxygen
Making that side
negative
Surface Currents
 Mapped by rubber duckies, bottles
World Surface Currents
 Driven by wind, Coriolis, continents
 Distribute heat from equator toward poles
Surface Currents: Pacific
Some flow into arctic ocean
Oya Siwo:
cold
current
soutward
past Asia
North Pacific
Drift brings
warm water
eastward
California
current
brings cold
water south
Kuro Siwo
warm
current to
north
Cold Peruvian
current brings
fish toward
shore
East
Australian
warm
current to
south
West Wind Drift circles Antarctcia
Surface Currents: Atlantic
COLD
Labrador
current drives
subsurface
currents
COLD Canaries
current past
Africa
West Wind
Drift
dominates
south Atlantic
currents
Gulf Stream
feeds North
Atlantic Drift,
dominates
north Atlantic
currents
Brazilian &
Benguela
currents
circle south
Atlantic
Gyres: Circular Currents
North Atlantic
Gyre
Turning and turning in the widening gyre
The falcon cannot hear the falconer;
Things fall apart; the centre cannot hold;
William Butler Yeats,
The Second Coming
Gyres
 Circular currents
 Eckman transport “mounds” water
 pushes water  to surface current
 Coriolis deflection balances gravity
Sea Level isn’t level!
Sea Level
 Sea level varies due to
 changes in local gravity (subsurface structure)
 currents (Eckman transport)
 Mean Sea Level
 Monitored by satellites
Low
Residuals = departure
from normal
High
Click for
Quicktime
Movie of Sea
surface height
and
temperature.
Regional Surface Currents
 Equatorial Currents
 Drive upwelling in east, spreading in west
Water deflects N & S due to
continents & Coriolis
Currents driven
by trade winds
Water leaving shore pulls water up
from below: upwelling
Regional Current Variations
 ENSO – El Niño Southern Oscillation
 Trade winds & equatorial currents slacken
Normal trade winds push
warm surface water to
Asia allowing upwelling of
cold, nutrient-rich, water
near South America
Slackened trade winds allow
warm water to slosh east,
stopping upwelling of nutrientrich water
Currents & Ocean Life
 Nutrients
 compounds of nitrogen, silicon, phosphorous
 minerals  carried by upwelling cold water
 Phytoplankton
 Fish food (bottom of the food chain)
 CO2 sink (absorb ½ Earth’s CO2)
 Some toxic (algae blooms, “red tides”)
 Fish
 Prefer living in warmer water
 Best fishing where cold & warm water meet!
 eg. The Outer Banks
Trigger unknown
Sea Surface
Temperature
monitored for
signs of building
El Niño
1997-98 El Niño
building
fading ……
ENSO
Regional Current Variations
 PDO – Pacific Decadal Oscillation
 Discovered in 1996 by Steven Hare researching
connection between Alaska Salmon & Pacific climate
 Warm (+) = Warm equatorial waters
In positive phase since April 2001
 Cool (-) = Warm water at high latitudes
Regional Current Variations
 PDO – Pacific Decadal Oscillation
 Currently in Positive phase (since April 2001)
 Fisheries in northeast pacific very productive
Regional Current Variations
 Gulf Stream
 Keeps Europe warm!!
 Drives worldwide currents
Deep Ocean Currents
 Thermohaline circulation
 Density of sea water
 increases with salinity
 decreases with temperature
Cold, salty water
sinks to bottom.
 Evaporation
 decreases water surface
temperature
 increases salinity
 Gulf Stream
Warm surface
water gets colder
and saltier than
subsurface water.
 warm surface water evaporates in N. Atlantic
cools, increases salinity ⇒ sinks to bottom
North Atlantic Downwelling
 Gulf Stream
 Bring warm water north … keep Europe warm!
 Cools, salinates, sinks, pulling more north
North Atlantic Downwelling
 Gulf stream waters sink to bottom
 Flow South along ocean bottom
 Drives Deep water circulation
Deep Ocean Circulation
 Great Conveyor Belt moving HEAT
 circuit takes about 2000 years
Deep Ocean Circulation
 Great Conveyor Belt moving HEAT
 circuit takes about 2000 years
Deep Ocean Circulation
 Great Conveyor Belt moving HEAT
 circuit takes about 2000 years
Ocean Conveyor Belt
 Can shut Down with too much fresh water
Thermohaline
Shutdown?
13,400 years ago Lake
Iroquois drained
through lake
Champlain and Hudson
Valley into Atlantic
Jeffrey Donnelly, WHOI,
December 2004, “Catastrophic
Flooding from Ancient Lake May
Have Triggered Cold Period ”
Thermohaline
Shutdown?
13,300 years ago Lake
Candona formed from
remnant of Lake
Iroquois
Jeffrey Donnelly, WHOI,
December 2004, “Catastrophic
Flooding from Ancient Lake May
Have Triggered Cold Period ”
Thermohaline
Shutdown?
13,100 years ago Lake
Candona increases as
glacier continues
retreating
Jeffrey Donnelly, WHOI,
December 2004, “Catastrophic
Flooding from Ancient Lake May
Have Triggered Cold Period ”
Thermohaline
Shutdown?
13,000 years ago Lake
Candona drains
through St. Lawrence
Valley, seawater
intrudes as Champlain
Sea
Jeffrey Donnelly, WHOI,
December 2004, “Catastrophic
Flooding from Ancient Lake May
Have Triggered Cold Period ”
Thermohaline Shutdown
 Gulf Stream stops warming Europe
 Europe cools dramatically
Lake Iroquois draining through Hudson Valley:
Intra-Alleroid Cold Period
Lake Candona draining
through St. Lawrence
Valley: Younger Dryas
Ocean Changes
 Temperature rising
 Cause of more and
more powerful
hurricanes?
The oceans have absorbed
about 30 times more heat than
the atmosphere since 1955
Oceans
Atmosphere
18.2 x 1022 J
6.6 x 1021 J
Curry, WHOI, OCCI
Ocean Changes
 Salinity
 Decreasing
in north
Atlantic
cf. Curry, WHOI, OCCI
 Salinity
Ocean Changes
 Decreasing at high latitude
 Increasing at low latitude
“ … deep waters have become less salty in critical North Atlantic
locations, where salty, dense waters sink to drive the global
ocean circulation system... ”
 Salinity
Ocean Changes
 Decreasing at high latitude
 Increasing at low latitude
“Global warming may be intensifying evaporation, adding
more fresh water vapor to the atmosphere and leaving
tropical oceans relatively saltier.”