1. Frank Bryan & Gokhan Danabasoglu NCAR
Ocean Initialization Issues for Transient Climate Change Ensemble Experiments
Frank Bryan & Gokhan Danabasoglu
NCAR

2. Assumptions & Biases
Our interest in these experiments include the simulation of the climate through the full 20th century as well as future projections.
By initialization we mean designing a sampling strategy to extract initial states from a pre-industrial control integration of the coupled system.
My comments reflect a personal research interest in the long-term behavior of the thermohaline circulation.

3. Recommendations for Transient Experiment Initialization Independent of Ensemble Size
Plan and budget for very long (1000+ year) pre-industrial control integrations sufficient to establish a period of stationary statistics that completely overlaps all planned transient integrations
Complete control integration(s) and characterize the statistics of their variability prior to starting climate change experiments.

4. Long-Term Behavior of Control MOC
Nakashiki et al (Ocean Modeling, submitted)

5. Characterize the Variability of the MOC
1990 Controls
CCSM3-T85x1
CCSM3-T42x1
CCSM2.2-T42x1
CCSM2-T42x1
CCSM3-T31x3

6. 1990 T85x1 Control MOC EOFs
17-25 years
G. Danabasoglu

7. Initializing Transient Experiments
1990 Control
1% CO2

8. 20th Century Ensemble Members and P-I Control

9. Ensemble Spread in Heat Storage
Gent et al (J. Clim., 2006)

10. Further Recommendations
Cross-WG research program over next 1.5 years to better characterize the global manifestations and physics of the MOC decadal mode.
What are the dynamical mechanisms of the decadal oscillations of the MOC?
Why does it appear to depend on model resolution?
Does the amplitude of the oscillation depend on the mean state?
What are the regional and global impacts of the variability?
What are the effects on predictability?

11. A Resource Conservative Initialization Strategy
Assuming dominant decadal mode exists:
Sample within a single oscillation period (20 to 50 years) of pre-industrial control.
Minimum 4-5 members for 20th century experiments
Consider dropping members for larger amplitude forcing and/or stabilization scenarios.
Samples phase space
Minimizes length of control run required