Sample lecture presentation from HON 305, Global Environment, on global atmospheric and oceanic circulation.

1. Global oceanic and atmospheric
circulation
HON 305V
Dr. Andersen

2. Atmospheric circulation: Simplistic
model
● Assume:
● Earth is not rotating
● Earth's surface is
uniform
● Global influx of solar
radiation and loss of
longwave radiation
creates a gradient of
decreasing
temperature from the
equator to the poles

3. Atmospheric circulation: Spin the
planet
● If you account for Earth's rotation, Coriolis
forces cause the circulation pattern to break
up into three cells (Hadley, Ferrel, and polar)
and two jet streams (subtropical and polar) in
each hemisphere
● Notice the weirdness at the north edge of the
Ferrel cell; this collision of warm and cold air
masses produces weather fronts and cyclonic
storms
● Intertropical convergence zone (ITCZ) follows
equator exactly

4. Actual global circulation
● Doesn't match up with 3-cell model for a couple of reasons
● Air heats and cools differently over land and water
● Elevation influences air flow, higher elevation often intensifies
pressure gradients
● Effects can be seen in global climate animations from the
University of Oregon, and also in these animations from
the National Center for Atmospheric Research (NCAR).
● Atmospheric circulation
● Vertical velocities
● Temperatures

5. Actual circulation: January
● Southern hemisphere
tilted toward sun
● ITCZ south of the
equator
● Big dips of ITCZ
toward the South
Pole over major land
masses because land
heats up faster than
ocean

6. Actual circulation: July
● ITCZ shifts to the north by as much as 40 degrees
latitude as northern hemisphere tilts toward the
sun
● Land areas of North Africa and Asia warm rapidly
to form an Asiatic low-pressure zone (contrast with
high pressure in that area in January) that
becomes part of the ITCZ, drives Asian monsoon
● Southern polar zone remains cold even during
southern hemisphere summer because Antarctic
ice sheet reflects most solar radiation

7. Oceanic circulation
● Generated by:
● Winds above surface waters (thus tied to atmospheric circulation)
● Evaporation
● Sinking of cold water at high latitudes
● Coriolis forces
● Flow patterns constrained by continents bordering the three ocean
basins (Atlantic, Pacific, and Indian), forming large-scale gyres
● Each gyre has two east-west currents (at top and bottom) and two
north-south currents along edges of continents
● Flow directions determined by prevailing winds and by Coriolis forces

9. ● Sometimes the Pacific Equatorial Counter
Current intensifies, driving El Nino conditions
● Western boundary currents flow from equator to
high latitudes, tend to be narrow and fast-
moving; the deepest oceanic surface currents
● Eastern boundary currents flow from high
latitudes to the equator, tend to be broad, slow-
moving, and shallow

10. Subsurface circulation
● Subsurface circulation much slower than surface
currents
● Driven by variation in the density of sea water
● Temperature
● Salinity
● Cold saline water sinks in the North Atlantic, flows to
(and then around) Antarctica, then northward into
Indian and Pacific Oceans, where it rises and joins
surface flow
● One complete circuit estimated to take about 1000
years

11. Video here

12. GCMs: Climate modeling
● Components
● Atmosphere
● Ocean
● Land surfaces
● Cryosphere (ice and snow)
● Associated biological and chemical processes
● Simplest GCMs consider either only atmosphere
(AGCM) or only ocean (OGCM)
● Newer more sophisticated GCMs include coupled
dynamics of most major systems (AOGCM), additional
links and components added frequently

13. GCMs
● U.N. Intergovernmental Panel on Climate
Change (IPCC) predictions based on coupled
models (AOGCM)
● Overall uncertainty depends on uncertainty of
component models
● Based on Navier-Stokes equations for fluid flow
with thermodynamic terms added
● Solved numerically on computer by
constructing a 3D grid over the Earth's surface

14. GCMs and climate change
● AOGCMs used to predict future climate under
various emissions scenarios
● Atmospheric greenhouse gas concentrations
typically simply an input to the model, although
it is possible to couple an AOGCM with a global
carbon-cycle model (and possibly an economic
model of global energy portfolios)

15. GCMs: Uncertainty
● Interaction with global carbon cycle one source
of uncertainty
● Another is the role of convective processes,
which generally take place at scales smaller
than the resolution of the model grid
● Major source of uncertainty is the role of
clouds; cloud formation and response to
changed climate not as well known as you
might expect

16. GCMs: Confidence
● Models are based both on physical law
(conservation of mass, Navier-Stokes
equations) and massive amounts of data
● Ability to simulate current climate based on first
principles
● Ability to provide insight into past climates and
climatic events (such as the climate impacts of
historic volcanic eruptions)

17. ● What are the main similarities between
atmospheric and oceanic circulation?
● Are any of the results of large-scale
atmospheric circulation apparent to the casual
observer?
● Why does it rain so much in the tropics?