Climate Dynamics

EPS 231 (Spring 2007)

Instructor: Eli Tziperman,

TF: Dorian Abbot, abbot@fas.harvard.edu

Day, time & location: Mon 5:00-6:30, Wed 4:00-5:30.
Location: Geological Museum room 105, entrance floor, 24 Oxford St.

Detailed teaching notes and links to source materials, Matlab codes and more

Homework:
HW-EBM-1,
HW-ENSO-1,
HW-ENSO-2,
HW-ENSO-4,
HW-THC-2,
HW-THC-3 due April 25,

Outline

The basics of climate dynamics, from the feedbacks that maintain the mean climate to phenomenology and mechanisms of climate variability. We will cover energy balance models, climate equilibria and stability with examples from equable climate to snowball earth. Examples of climate variability to be covered are El Nino (occurring roughly every 4 yrs), the thermohaline circulation and its multiple equilibria and variability (decadal and longer); thermohaline variability as a possible explanation for the medieval warm period and the little ice ate (hundreds of years); the Dansgaard-Oeschger warming events observed in the Greenland ice core (every 1500 yr), Heinrich events involving massive collapses of ice during glacial times (every 7-10,000yr) and glacial-interglacial variability (100,000 yr). In each case, we will discuss physical mechanisms and demonstrate them with a hierarchical modeling approach, from toy models to GCMs. Needed background in nonlinear dynamics will be covered.

Familiarity with some basic Geophysical Fluid Dynamics (the equivalent of MIT 12.800, or Harvard EPS 131, EPS 132 or EPS 232), or general fluid dynamics (e.g. engineering fluid courses at Harvard) will be assumed. The course may be taken as a sequel to MIT's Climate Physics and Chemistry (12.842), but can also be taken independently of that course.

Course homepage: http://www.deas.harvard.edu/climate/eli/Courses/2007spring_b/

First lecture (ppt),

Textbooks

• Hartman, physical climatology (Hartmann, 1994)
• Gill, atmosphere-ocean dynamics (Gill, 1982)
• Dijkstra, nonlinear physical oceanography (Dijkstra, 2000)

Detailed syllabus

A detailed outline of the lectures, and a complete list of reference materials used in each lecture is available here.

1. Outline and motivation.
2. Basic climate feedbacks. Supporting material may be found here.
   1. radiation, energy balance, albedo, ice, clouds
   2. climate stability, budyko-sellers model, snowball.
3. El Nino - Southern Oscillation (Cessi et al., 2001); additional supporting material may be found here.
   1. Phenomenology: basics: Gill atmosphere; reduced gravity models, equatorial ocean waves (Dijkstra, 2000), (Gill, 1982).
   2. Coupled ocean-atmosphere dynamics, demonstrated via the Cane-Zebiak model
   3. Delayed oscillator
   4. ENSO regimes: fast SST, fast wave, mixed; recharge oscillator:
   5. Irregularity: chaos
   6. Irregularity: stochastic forcing, non normal dynamics, optimal initial conditions and stochastic optimals
   7. Westerly wind bursts
   8. Locking to seasonal cycle
   9. Atmospheric teleconnections
4. Equable climate lecture additional supporting material may be found here.
5. Thermohaline circulation (Dijkstra, 2000); additional supporting material may be found here.
   1. Phenomenology, mixed boundary conditions, Stommel model
   2. Advective and convective feedbacks; flip flop and loop oscillations.
   3. Stability, bifurcations and multiple equilibria
   4. Stochastic forcing; linear vs nonlinear; non normal dynamics, noise induced transitions between steady states
   5. Thermohaline flushes (``deep decoupling'' relaxation oscillations)
   6. Zonally averaged models and closures to 2d models.
   7. Atmospheric feedbacks
6. D/O and Heinrich events: supporting material may be found here.
   1. DO:THC flushes vs sea ice changes;
   2. Heinrich events: binge-purge oscillator, climatic effects, synchronous collapses
7. Glacial cycles: supporting material may be found here.
   1. Phenomenology
   2. Milankovitch forcing
   3. Energy balance atmosphere
   4. Ice sheets: mass balance, geometry, parabolic profile.
   5. Glaciology basics: Glenn's law, basic solutions equilibrium profiles of ice sheets and ice shelves.
   6. Simple models of glacial cycles
   7. Phase locking to Milankovitch forcing

Requirements

Homework assignments are 50% of final grade, and a final course project will constitute the remaining 50%. There is an option to take this course as a pass/fail with approval of instructor. If interested, you need to obtain this approval during the first three weeks of the course.

Links

• Woods hole summer GFD school notes on ENSO and glacial cycles,
• energy balance models

Bibliography

Cessi, P., Pierrehumbert, R., and Tziperman, E. (2001).

Lectures on enso, the thermohaline circulation, glacial cycles and climate basics.
In Balmforth, N. J., editor, Conceptual Models of the Climate. Woods Hole Oceanographic Institution, http://gfd.whoi.edu/proceedings/2001/PDFvol2001.html.

Dijkstra, H. A. (2000).

Nonlinear physical oceanography.
Kluwer Academic Publishers.

Gill, A. E. (1982).

Atmosphere-Ocean Dynamics.
Academic Press, Inc, San Diego, CA, 662pp.

Hartmann, D. (1994).

Global Physical Climatology.
Academic press, San Diego.