Instructor:

Eli Tziperman

TF:

Wanying Kang, wanyingkang@g.harvard.edu

Day, time:

Tuesday, Thursday, 1:30-2:45

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

The course covers climate dynamics and climate variability phenomena and mechanisms, and provides hands-on experience running and analyzing climate models, as well as using dynamical system theory tools. The material includes 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 with Snowball Earth as an example. Climate variability: El Nino (roughly 4 yr period), 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 cores (every 1500 yr), Heinrich events involving massive collapses of ice during glacial times (every 7-10,000 yr), glacial-interglacial variability (100,000 yr) including ocean, atmospheric and ice dynamics, ocean carbonate chemistry and CO2. Warm climates, from the Pliocene’s (3-5 Myr) permanent El Nino to the Eocene (50 Myr) equable climate, and with lessons to possible surprises in a future warmer 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 these courses. Familiarity with some basic Geophysical Fluid Dynamics (the equivalent of MIT 12.800, or Harvard EPS 232) is assumed; (student who took EPS 131 or EPS 132 and are interested in taking the course are requested to contact the instructor).

Course homepage: http://www.seas.harvard.edu/climate/eli/Courses/EPS231/2019spring/

2 Textbooks

• Hartman, physical climatology
• Gill, atmosphere-ocean dynamics
• Dijkstra, nonlinear physical oceanography
• Vallis, Atmospheric and oceanic fluid dynamics, fundamentals and large-scale circulation
• Cessi, Pierrehumbert and Tziperman, Lectures on ENSO, the Thermohaline circulation, glacial cycles and climate basics, Woods Hole Oceanographic Institution

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, greenhouse, bifurcations, hysteresis and snowball
   2. (Time permitting) Small ice cap instability
3. El Nino - Southern Oscillation supporting material.
   1. Phenomenology: basics: Gill atmosphere; reduced gravity models, equatorial ocean waves
   2. Coupled ocean-atmosphere dynamics, demonstrated via the Cane-Zebiak model
   3. Delayed oscillator
   4. (Time permitting) 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, Rossby ray tracing
4. Thermohaline circulation 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:
   4. Ice sheets and glaciology basics: Glenn’s law, mass balance, equilibrium parabolic profile,
   5. Proposed mechanisms for glacial cycles
   6. Phase locking to Milankovitch forcing
   7. CO₂ and the ocean carbonate system
7. Pliocene, 2-5Myr. supporting material.
   1. Major problems: “permanent El Nino”, warming of mid-latitude upwelling sites
   2. Proxies, proxies, proxies.
   3. Proposed ideas
8. Equable climate supporting material. Proposed mechanisms:
   • Equator to pole Hadley cell
   • Polar stratospheric clouds
   • Hurricane mixing of ocean
   • Convective cloud feedback
9. Data analysis tools for observations and model output (hands-on practice in sections). supporting material.
   • EOFs
   • SVD analysis of two co-varying fields
   • Composite analysis
   • Linear inverse models, POPs
   • Spectral analysis
10. Review. supporting material.

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