1. EPS 231, Climate dynamics
Eli Tziperman; Museum building 456, 24 Oxford St. ;
TF: Lauren Kuntz
Course web page, teaching notes, downloads:
Textbooks:
Vallis: Atmospheric and oceanic fluid dynamics
Dijkstra, nonlinear physical oceanography,
Hartman, global physical climatology
Strogatz, nonlinear dynamics and chaos,
Needed background: basic Fluid dynamics/ GFD (MIT12.800, EPS 131/132/232, engineering fluid dynamics, etc)
Odyssey account: apply now! For GCM analysis experience
Requirements: HW every 9-10 days (50%); final project (50%)

2. Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
Outline
Energy balance: multiple equilibria, small ice cap instability, relevance to recent Arctic sea ice melting & Snowball Earth
El Nino: (4 yrs) delayed oscillator, stochastic & chaotic irregularity, teleconnections via stationary Rossby Waves
THC: ( yrs) Multiple equilibria, abrupt transitions, advective & convective feedbacks, variability & oscillations
Dansgaard-Oeschger & Heinrich events: ( yrs) due to THC variability and ice sheet collapses.
Glacial cycles: (105 yrs) mechanisms, Milankovitch, CO2, ice
Warm climate: (3-5x106 yrs, Pliocene), permanent El Nino
Equable climate: (50x106 yrs, Eocene) Hadley cell, hurricanes, polar stratospheric clouds, convective cloud feedback.
Tools: observations, proxy observations, hierarchy of modeling tools from conceptual (toy) models to hands-on GCM analysis.

3. EPS 231, Climate dynamics, review!

4. Energy balance, small ice cap instability
Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
Energy balance, small ice cap instability
Small ice cap instability:
Polar ice cap can only be sustained if over a minimal size roughly corresponding to present-day arctic sea ice cover.
Run away ice albedo, snowball events:
Ocean frozen to a depth of ~1km, land ice-covered for Myrs
Termination due to co2 emissions from volcanoes?
Initiation trigger?
Evolutionary consequences?
Predicted by Budyko-Sellers (1969) energy-balance toy model

5. El Nino – Southern Oscillation (ENSO)
Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
El Nino – Southern Oscillation (ENSO)
Sea surface temperature, 1997: strongest El Nino in 100 years
Mechanism: ocean waves, thermocline, SST; atmospheric heating, winds; & ocn - atm coupling

6. ENSO ENSO is irregular (nino3 SST), yet locked to seasonal cycle
Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
ENSO
ENSO is irregular (nino3 SST), yet locked to seasonal cycle
teleconnections

7. Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
ENSO
Equatorial waves
Ocean-atmosphere coupling: SST  wind  thermocline depth  SST
Delayed oscillator, role of delayed Rossby waves
Irregularity:
Transient amplification/ stochastic optimals
Chaos: quasi-periodicity route to chaos driven by seasonal cycle
Teleconnections, atmospheric RW, ray tracing, WKB
Final review

8. Thermohaline circulation (THC/MOC)
Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
Thermohaline circulation (THC/MOC)
Transport: 20 x world rivers combined. Warms Europe…?
Driven by temperature & salinity gradients + more
Can become unstable, multiple equilibria, hysteresis, … affects climate on a hundred-year time scale
A winter scene in Europe's Little Ice Age, 14th Century
Pieter Breugel the Elder.

9. THC: Little ice age, medieval warm period
Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
THC: Little ice age, medieval warm period
Norse ruins from Brattahlid, Greenland. “Eirik the Red,” exiled from Iceland for his crimes, 980 A.D., set sail and spotted “Greenland”. 1,000 Scandinavians lasted until 1480 A.D., died by starvation due to nasty winters.

10. THC/ MOC Stommel box model, multiple equilibria, hysteresis
Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
THC/ MOC
Stommel box model, multiple equilibria, hysteresis
Convective and advective thermohaline feedbacks
Variability mechanisms:
Convective oscillations, Welander’s flip-flop and friends
Advective oscillations
Self-sustained oscillations vs noise driven (transient growth, stochastic optimals)
Relaxation oscillations of the THC/ MOC
Final review

11. Dansgaard-Oeschger Events
Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
Dansgaard-Oeschger Events
DO events in Greenland ice cores:
Warmings occur every ~1500yr
~10 deg C warming
Start & end within 20 yrs!
Warmings last yrs
Mechanism:
THC + sea ice?

12. Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
Heinrich events
Ice Rafted Debris (IRD) sediment layers due to massive glacier discharges from Laurentide & other ice sheets, every 7-10,000 yr.
Occurred 20-60,000 ago
Possibly synchronous collapses/ discharges of several ice sheets
Cold/ warm periods seen in ice core record as part of a Heinrich cycle…
Mechanism: Bing/purge + THC + sea ice?
Typical sediments
Ice rafted debris

13. Dansgaard-Oeschger & Heinrich events
Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
Dansgaard-Oeschger & Heinrich events
Observations: ice cores and sediments
MOC/ THC flushes
Amplification of atmospheric response by sea ice changes
Precise clock behind DO events?
DO teleconnections
Heinrich events: basal melting and binge-purge mechanism
Final review

14. Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
Largest climate signal in past 3Myrs. Still not understood:
Mechanism/ forcing?
What caused CO2 to change?
Role of Milankovitch forcing?
Ice flow basics

15. Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
Glacial cycles, more
Why the transition from 40kyr to 100 kyr about 800kyr ago?
Ice ages during past 600,000 yrs
Last 5.5 Myr: ice ages started 2.7 Myr ago; occurred every 40 kyr until 800,000 yr & every 100 kyr since

16. Glacial cycles Observations &major problems:
Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
Glacial cycles
Observations &major problems:
100 kyr, 41 kyr, mid-Pleistocene transition, CO2 changes
Ingredients & basics:
Energy balance, ice dynamics and Glenn’s law, ice streams, calving, temperature-precipitation feedback, isostatic adjustment, geothermal heating, ocean heat transport, Milankovitch …
Mechanisms: “more theories than theoreticians”, but still some robust lessons:
Phase locking to Milankovitch as a robust feature; need for a self-sustained oscillations that’s able to phase lock
From curve fitting to falsifiable mechanisms
Integrated insolation and 41 kyr oscillations
CO2:
intro to ocean biogeochemistry
explaining glacial-interglacial CO2 variations.
Final review

17. “Permanent El Nino” during the Pliocene, 2-5Myr
Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
“Permanent El Nino” during the Pliocene, 2-5Myr
[Wara et al 2005]
[Medina Elizalde et al 2008]
 The east-west temperature gradient in the equatorial Pacific did not exist during the Pliocene (2-5 Myr ago)

18. Warm Climates: Pliocene, 2-5 Myr
Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
Warm Climates: Pliocene, 2-5 Myr
Observations & major problems:
Permanent El Nino(?)
Major warming of mid-latitude coastal upwelling sites
Proxies, proxies, proxies.
Mechanisms considered:
Thermocline collapse (deepening) due to FW flux
Tectonics: opening of central American seaway
Tectonics: island movement to block equator in west Pacific
Hurricanes and ocean mixing
Atmospheric superrotation due to meridional eddy momentum fluxes by Rossby Waves
Final review

19. Pliocene climate ideas
Open central American seaway [Steph et al 2010]
collapse equatorial thermocline w/ N. Pacific fresh water flux [Fedorov et al 2004/2006]
Move Papua/ New Guinea;
[Cane&Molnar 2001;
Hurricanes/ ocean mixing [Emanuel 2002… Fedorov et al 2010/2013]
Change easterlies via R.W. induced Superrotation

20. Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
Observations: very warm climate ~ Myr ago: deep ocean ~15C; above freezing winter temperatures at 60N, Greenland & middle of Canada (now -30C); equator to pole Temp gradient ~ 25 (now >40).
The mystery(?): Warm continental winter climate cannot be reproduced by GCMs even at very high CO2 levels
Modern Model SST
- Eocene Model SST
Eocene Proxy SST
Eocene Model SSS
Present-day like geometry
[Huber and Sloan, 2001]

21. Equable climate ideas Hurricanes and ocean mixing/ THC
Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
Equable climate ideas
Hurricanes and ocean mixing/ THC
Hurricanes and ocean mixing/ THC
Convective tropospheric cloud feedback
Polar stratospheric clouds (15-25km)

22. And thanks for a great semester…
Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
The End
Thanks Lauren!
And thanks for a great semester…
Final review

24. Let the fun begin…

25. Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate
Let’s get started…

26. Climate dynamics & physical oceanography
Eli Tziperman
Museum building 456b
The oceanography we need today…

27. Monsoon variability (~2 years)
CNN, Aug 2000: Millions of people in 3 eastern states homeless by rains; 24 cm rain in a few days; highest in 50yr.

28. Monsoons: An intersection of science and societal issues
Indian monsoons: what causes year to year variability of monsoon precipitation?
Complex relations to El Niño, Tibetan snow, atmospheric dynamics, ocean circulation...
Affects Indian agriculture, flooding, erosion, disease…
Predictability?