Instructor:

Eli Tziperman,

TF:

Chris Horvat, horvat at fas.harvard.edu

Day, time:

Monday 2:30-4:00, Thursday, 2:30-4;

Location:

Geological Museum, 4th floor, room 418. 24 Oxford St, Cambridge.

Contents

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

1 Outline

Principles of climate dynamics, from feedbacks that maintain different mean climates, to phenomenology and mechanisms of climate variability on multiple time scales. Energy balance and climate equilibria, stability and bifurcations, Snowball Earth as an example. Climate variability: 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 age (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 7-10,000 yr), glacial-interglacial variability (100,000 yr) from relevant climate and ice dynamics to ocean carbonate chemistry and CO2. Warm climates, from the Pliocene’s (3-5 Myr) permanent El Nino to the Eocene (50 Myr) equable climate. In each case, we will discuss physical mechanisms and demonstrate them with a hierarchical modeling approach, from toy models to General Circulation Models. Needed background in nonlinear dynamics will be covered.

The course may be taken as a sequel to MIT’s Climate Physics and Chemistry (12.842) or Harvard’s introduction to climate physics (EPS 208), but can also be taken independently of that course. Familiarity with some basic Geophysical Fluid Dynamics (the equivalent of MIT 12.800, or Harvard EPS 131, EPS 132 or EPS 232) is assumed.

Course homepage: http://www.seas.harvard.edu/climate/eli/Courses/EPS231/2015spring/

2 Textbooks

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

3 Detailed syllabus

A detailed outline of the lectures, and a complete list of reference materials used in each lecture is available here. The course Supporting materials are available here. If accessing from outside campus or via the university wireless network, you will need to connect via the Harvard VPN.

1. Outline and motivation: First lecture (ppt),
2. Basic climate feedbacks. Supporting material.
   1. energy balance
   2. small ice cap instability
3. El Nino - Southern Oscillation (Cessi et al., 2001); supporting material.
   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 (section 4, eqns 11-14, Tziperman and Ioannou, 2002).
   7. Westerly wind bursts
   8. Locking to seasonal cycle
   9. Atmospheric teleconnections, Rossby ray tracing
4. Thermohaline circulation (Dijkstra, 2000); supporting material.
   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)
5. D/O and Heinrich events: supporting material.
   1. DO: THC flushes vs sea ice changes;
   2. Heinrich events: binge-purge oscillator, climatic effects, synchronous collapses
6. Glacial cycles: supporting material.
   1. Phenomenology
   2. Milankovitch forcing
   3. Ice sheets: mass balance, geometry, parabolic profile.
   4. Glaciology basics: Glenn’s law, basic solutions equilibrium profiles of ice sheets and ice shelves.
   5. Simple models of glacial cycles
   6. Phase locking to Milankovitch forcing
   7. CO₂ and the ocean carbonate system
7. Equable climate supporting material.
   • Equator to pole Hadley cell
   • Polar stratospheric clouds
   • Hurricane mixing of ocean
   • Convective cloud feedback

4 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.

5 Links

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

References