EPS 231: Climate Dynamics
Spring 2023
Canvas course web page for EPS 231
last updated: Tuesday 11th April, 2023, 15:49
This is:
Earth and Planetary Sciences 231: Climate Dynamics.
Instructor:
TF:
Camille Hankel, Camille_Hankel@g.harvard.edu. Office hours: Canvas course website.
Day, time:
Tuesday, Thursday, 10:30–11:45
Location:
Geological Museum, 4th floor, room 418. 24 Oxford St, Cambridge.
Office hours:
Eli: Monday/ Wednesday 1–2, please feel free to write or call me with any questions.
Electronic homework submission:
via https://www.gradescope.com/courses/408399: upload your submission as pdf following this tutorial video.
Course forum:
Please post questions regarding HW to the course forum on Ed Discussions (https://edstem.org/us/courses/30869/discussion/), you are very welcome to respond to other student questions.
Course downloads:
http://www.seas.harvard.edu/climate/eli/Courses/EPS231/Sources/
Detailed teaching notes:
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 Niņo (~4 yr period), the meridional overturning circulation and its multiple equilibria and variability (decadal and longer); meridional overturning 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 Niņo 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. The needed background in nonlinear dynamics will be covered.
Course homepage: http://www.seas.harvard.edu/climate/eli/Courses/EPS231/2023spring/
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; (students who took EPS 131 or EPS 132 and are interested in taking the course are requested to contact the instructor).
A detailed outline of the lectures, and a complete list of reference materials used in each lecture is available here. The course Supporting materials including slides, notes and code are available here.
Outline and motivation: supporting material,
Basic climate feedbacks: supporting material.
Energy balance, greenhouse, bifurcations, hysteresis and snowball
(Time permitting) Small ice cap instability
El Niņo—Southern Oscillation: supporting material.
Phenomenology: basics: Gill atmosphere; reduced gravity models, equatorial ocean waves
Coupled ocean-atmosphere dynamics
Delayed oscillator/recharge oscillator:
Irregularity: chaos, nonlinear phase locking to the seasonal cycle
Irregularity: stochastic forcing, non-normal dynamics, optimal initial conditions and stochastic optimals.
Westerly wind bursts as state-dependent stochastic forcing.
Atmospheric teleconnections, Rossby ray tracing
ENSO diversity
Meridional overturning circulation: supporting material.
Phenomenology, mixed boundary conditions, Stommel model
Stability, bifurcations, multiple equilibria, tipping points
Advective and convective feedbacks; flip flop and loop oscillations.
Stochastic forcing; linear vs nonlinear; non-normal dynamics, noise-induced transitions between steady states
D/O and Heinrich events: supporting material.
DO: AMOC flushes vs sea ice changes;
Heinrich events: binge-purge oscillator, climatic effects, synchronous collapses
Glacial cycles: supporting material.
Phenomenology
Milankovitch forcing
Ice sheets and glaciology basics: Glenn’s law, mass balance, equilibrium parabolic profile
Proposed mechanisms for glacial cycles
Phase locking to Milankovitch forcing
CO2 and the ocean carbonate system
Pliocene, 2–5Myr: supporting material.
Major two problems: “permanent El Niņo”, and the dramatic warming of mid-latitude upwelling sites.
Proxies, proxies, proxies.
Proposed ideas for explaining the “permanent El Niņo”:
Tectonic movement of Papua/ New Guinea
Opening of the central American seaway
Hurricanes and ocean mixing
Collapse of the equatorial thermocline due to enhanced N. Pacific precipitation
Atmospheric superrotation
Equable climate: supporting material.
The challenge: the existence of frost-intolerant flora and fauna (palm trees and alligators) in high-latitude mid-continental areas.
Proposed ideas:
Equator-to-pole Hadley cell
Polar stratospheric clouds
Hurricane mixing and ocean MOC
Breakup of subtropical marine stratocumulus clouds
Low clouds suppressing Arctic air formation
Convective Arctic cloud feedback
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
Review. supporting material.
Assignments from a recent time this course was taught, although not necessarily from this current year, are available here; please email if you are teaching a similar course and are interested in the solutions.
Homework assignments every 9–10 days are 50% of the final grade, and a final course project constitutes the remaining 50%. There is an option to take this course as a pass/fail with an instructor’s approval during the first week of classes. The subject of the final project would be discussed in a couple of individual meetings with students during the semester, and would ideally be related to either climate subjects, modeling approaches, nonlinear dynamics methods or data analysis covered in class, and may be related to the research project of the student. The length of the final report should be some 6–10 pages including a few figures, 12pt, in pdf format, and the expected effort is of some 6–8 days of work. Please include an abstract, an introduction with the background/ motivation, a methods section including the precise details of data sources or model versions/ configuration with relevant links, results, and discussion/ conclusions.
Collaboration policy. We strongly encourage you to discuss and work on homework problems with other students and with the teaching staff. Of course, after discussions with peers, you need to work through the problems yourself and ensure that any answers you submit for evaluation are the result of your own efforts, reflect your own understanding and are written in your own words. In the case of assignments requiring programming, you need to write and use your own code. Please appropriately cite any books, articles, websites, lectures, etc that have helped you with your work.