Transcript Temperature - Harvard University

Introduction to physical oceanography & climate
EPS 131
Times: Monday, Thursday 2:30-4:00;
Location: University Museum, 24 Oxford - 105 (Daly Seminar Room)
Eli Tziperman
Museum building 456, 24 Oxford St
Tel: (617) 384-8381; [email protected]
Office hours: Tuesday 1:30-3, Thursday 1-2
TF: Chris Horvat, [email protected]
Tel, office: , office hours: please see course web page.
Please feel free to write/ call/ visit us…
Announcements, notes, homework, solutions:
http://isites.harvard.edu/k95675
EPS131 logistics
Course requirements: Best 90% of quasi-weekly homework (40% of
grade); 2 class presentations (30%); Final (possibly a take home,
30%). Woods Hole field trip.
Needed preparation: APM 21a,b/ Math 21a,b; Physics 15/12,AP50; no
programming preparation expected, Matlab will be introduced & used
Matlab Intro sessions: Please see course web page
Textbook(s): Knauss, introduction to physical oceanography, 2nd edition,
1996, Also useful: The open university team: (1) Ocean circulation,
2nd ed, 2002; (2) Waves, tides and shallow water processes, 2nd ed,
2002. (3) Kundo & Cohen, Fluid mechanics. 2nd ed ’02; (4) Stewart,
on-line physical oceanography book.
Course web page: homework, announcements, student presentations …
http://isites.harvard.edu/k95675
Teaching notes with links to on-line sources for lectures:
http://www.seas.harvard.edu/climate/eli/Courses/EPS131/2014spring/teac
hing-notes-intro-physical-oceanogr.pdf
temperature, salinity | currents, Coriolis | waves | observations | climate
Outline
 The basics, what we observe:
 Solar forcing  ocean temperature, salinity
 Solar forcing  winds  Currents, Coriolis force
 Winds + continents  Gulf stream,
 Variability of ocean circulation, rings, eddies
 Waves: from beach waves to tides & Tsunamis
 How we observe: Ships, satellites, airplanes, moorings, current
meters, buoys, floats, sound waves...
 Oceans and climate: Monsoons, Thermohaline circulation; El Nino;
abrupt climate change, glacial cycles; global warming, …
 How we try to understand it all: From theory to data analysis; From
pencil/ paper to super computers
temperature, salinity | currents, Coriolis | waves | observations | climate
Temperature
http://www.applet-magic.com/insolation.htm
Solar
radiation as
function of
latitude and
month
leads to cold high latitudes, warm tropics:
Horizontal map of sea surface temperature
temperature, salinity | currents, Coriolis | waves | observations | climate
Temperature
Mixed layer
Vertical
temperature
profile
Thermocline
Are both evidence of a meridional circulation
North-South Section. Bottom temperature is near 0 deg even at Equator
temperature, salinity | currents, Coriolis | waves | observations | climate
Salinity
?? kg salt/meter cubed
Evaporation, precipitation, ice melt…
lead to salinity variations in space and time:
And also indicates the presence of a
large-scale meridional circulation:
Salinity along Atlantic ocean, vertical axis exaggerated by 1000s
temperature, salinity | currents, Coriolis | waves | observations | climate
Sun also drives winds which force a horizontal
ocean circulation (wind-driven gyres)
…drive global circulation circulation
Global winds…
schematic of wind-driven ocean gyres
temperature, salinity | currents, Coriolis | waves | observations | climate
Coriolis force
(J. Marshall, MIT)
Ocean currents
are dramatically
affected by Earth
rotation &
resulting Coriolis
force
Toilet Bowl Water Twirls
Clockwise?
Coriolis force is to right
of motion in north
hemisphere; left in
south
temperature, salinity | currents, Coriolis | waves | observations | climate
Coriolis force, Coastal Upwelling and fisheries
Currents driven by winds & diverted by
Coriolis force, transport water away
from shore. Deep, cold water upwells to
compensate.
The rising water is rich in nutrients,
attract plankton & create rich fisheries.
Temperature and chlorophyll
concentrations along the
California coast
temperature, salinity | currents, Coriolis | waves | observations | climate
Coriolis force, highs/lows, ocean surface “topography”
• Air/water does not flow from high
to low pressure…
• Instead, Coriolis force causes
flow along equal pressure lines
• Surface height difference across
width of Gulf Stream (50km) is
~one meter (!)
temperature, salinity | currents, Coriolis | waves | observations | climate
Gulf Stream/ Kuroshio: western boundary currents
(Strong western vs weaker eastern boundary currents)
Note east-west
Asymmetry!
1753-1774, deputy
postmaster general,
North America
Cold California
Current: 2M m3/sec;
0.1m/s
Warm Gulf Stream:
150 M m3 /sec, 1- His cousin’s map of a
feature known for 250 yr
2m/s
temperature, salinity | currents, Coriolis | waves | observations | climate
Ocean Eddies
●
●
●
1970s: ocean is continuously changing
There is turbulence in the ocean on all
scales from mm to 100s km. The large
turbulent features are “eddies”
Similar to weather systems, but X10
smaller; move/ change slower (weeks &
months instead of days)
Chlorophyll-a from ocean color,
SeaWIFS, East Australia Current
Temperature, US east coast
temperature, salinity | currents, Coriolis | waves | observations | climate
Waves, Tides, Tsunami
surface waves
internal waves
planetary waves (of jet stream)
temperature, salinity | currents, Coriolis | waves | observations | climate
Waves, Tides, Tsunami
●
causes?
●
why two a day?
●
why large in some
places & small in
others?
Mont-Saint-Michel (town of Normandy - France)
temperature, salinity | currents, Coriolis | waves | observations | climate
Waves, Tides, Tsunami
• caused by undersea
earthquakes, landfalls
• propagate as undetectable
low-amplitude surface waves
• speed= gH  200m / sec  400mph
• slow down and height
increases to 10s m when
approaching shallow coast.
2004; http://www.thelivingmoon.com
1992, Indonesia, 3-4m waves
TOPEX
Observing the oceans
temperature, salinity | currents, Coriolis | waves | observations | climate
Ships, satellites,
moorings, floats
Challenger, 1870s
World Ocean Circulation
Experiment, 1990s
(EPS131 field trip to WHOI @ cape
code during the term…)
temperature, salinity | currents, Coriolis | waves | observations | climate
Ships, satellites,
moorings, floats
Satellites observe surface
temperature, salinity, height,
winds, waves, ice, chlorophyll &
more; not ocean interior…
Altimeter: radar measuring
ocean surface height
temperature, salinity | currents, Coriolis | waves | observations | climate
Ships, satellites,
moorings, floats
temperature, salinity | currents, Coriolis | waves | observations | climate
TOPEX
Ships, satellites,
moorings, floats
Argo
float
Argo floats that
delivered data during
past 30 days
Argo floats cycle between 2000m and
surface every 10 days & drift with currents
Climate!
●
Thermohaline circulation
●
Abrupt climate change
●
El Nino
●
Future climate change
temperature, salinity | currents, Coriolis | waves | observations | climate
Thermohaline circulation & Global climate
●
THC carries 20M meter cubed of water
per second (all rivers combined: 1M)
●
Carries a significant part of the heat transport
from the equator to the pole
●
Driven by temperature differences, “braked” by salinity
●
May vary on a time scales of decades, affecting European climate
●
Its past variations may have caused abrupt climate change. “Day
after tomorrow…”
temperature, salinity | currents, Coriolis | waves | observations | climate
The THC and past climate
Europe's Little Ice Age, 14th
Century; Pieter Breugel the Elder.
Norse ruins from
Brattahlid, Greenland.
“Eirik the Red,” exiled from
Iceland for his crimes, 980
A.D., set sail and spotted
“Greenland”. 1,000
Scandinavians lasted until
1480 A.D., died by
starvation due to nasty
winters.
temperature, salinity | currents, Coriolis | waves | observations | climate
Abrupt past climate change
(due to thermohaline circulation changes?)
Global warming D/O & Heinrich events
Amplitude
0.75C
Duration of change 100 years
10C
20 years
temperature, salinity | currents, Coriolis | waves | observations | climate
El Nino
Observed sea surface
temperature anomaly during 1997
event
Observed sea surface
temperature during 1982 & 1997
temperature, salinity | currents, Coriolis | waves | observations | climate
Observations: is El Nino changing?
Nino 3 SST
30
29
28
oC
• Period 3-6 years
27
26
• Irregular cycle
difficult to predict
25
24
23
1900
• Recent changes
due to global
warming or decadal
variability?
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
1970
1980
1990
2000
Nino 3 SST
30
29
28
oC
27
26
25
24
23
1900
1910
1920
1930
1940
1950
1960
Back to the future
temperature, salinity | currents, Coriolis | waves | observations | climate
Ocean’s role in global warming
●
●
Sea level rise
Abrupt climate change: sea ice;
THC
●
Absorbing ½ of emitted CO2
●
Ocean acidification
temperature, salinity | currents, Coriolis | waves | observations | climate
Summary
 The basics, what we observe:
 Solar forcing  ocean temperature, salinity
 Solar forcing  winds  Currents, Coriolis force
 Winds + continents  Gulf stream,
 Variability of ocean circulation, rings, eddies
 Waves: from beach waves to tides & Tsunamis
 How we observe: Ships, satellites, airplanes, moorings, current
meters, buoys, floats, sound waves...
 Oceans and climate: Monsoons, Thermohaline circulation; El Nino;
abrupt climate change, glacial cycles; global warming, …
 How we try to understand it all: From theory to data analysis; From
pencil/ paper to super computers