1. Ensemble Spread and Resolution in Minerva Simulations
Ben Cash and Jieshun Zhu
Minerva Project Team
Minerva Workshop, GMU/COLA,
September 16, 2013

2. Role of Resolution in Minerva Simulations
Significant Differences in Atmosphere, Ocean Components
Multiple atmosphere resolutions
64, 32, and 16 km
Single ocean resolution
1 degree, telescoping to 1/3 degree
Lower resolution than ‘low’ resolution atmospheric case in extratropics, comparable near equator
Given difference in scales, how much impact does atmospheric resolution have on ocean?
Ensemble mean SST relatively insensitive to resolution
What about higher order statistics?

3. Clear difference in ensemble spread between T639 and T319
Significance? Focus on differences in ratio of ensemble variance
Significance determined by F-test

4. Ratio of Ensemble Variance: T639 / T319 SST
May Values (May Initial Conditions)

5. Ratio of Ensemble Variance: T639 / T319 SST
June Values (May Initial Conditions)

6. Ratio of Ensemble Variance: T639 / T319 SST
July Values (May Initial Conditions)

7. Ratio of Ensemble Variance: T639 / T319 SST
August Values (May Initial Conditions)

8. Ratio of Ensemble Variance: T639 / T319 SST
September Values (May Initial Conditions)

9. Ratio of Ensemble Variance: T639 / T319 SST
October Values (May Initial Conditions)

10. Ratio of Ensemble Variance: T639 / T319 SST
November Values (May Initial Conditions)

12. Intra-ensemble variance of SST increases significantly from T319 to T639
Increase focused primarily in the tropics and subtropics
Result insensitive to choice of period or (not shown)
What about T639 to T1279?

13. Ratio of Ensemble Variance: T1279 / T639 SST
November Values (May Initial Conditions)

14. No significant change from T639 to T1279
Consistent with Athena results suggesting many processes captured successfully at T511
Suggestion of difference in tropical Atlantic, further evidence of tropical origin of difference?
Impact of these differences on overall simulation?
Are differences confined to SST?

15. Ratio of Ensemble Variance: T639 / T319 Thermocline Depth
May Values (May Initial Conditions)

16. Ratio of Ensemble Variance: T1279 / T639 Thermocline Depth
June Values (May Initial Conditions)

17. Ratio of Ensemble Variance: T1279 / T639 Thermocline Depth
July Values (May Initial Conditions)

18. Ratio of Ensemble Variance: T1279 / T639 Thermocline Depth
August Values (May Initial Conditions)

19. Ratio of Ensemble Variance: T1279 / T639 Thermocline Depth
September Values (May Initial Conditions)

20. Ratio of Ensemble Variance: T1279 / T639 Thermocline Depth
October Values (May Initial Conditions)

21. Ratio of Ensemble Variance: T1279 / T639 Thermocline Depth
November Values (May Initial Conditions)

22. Thermocline pattern much noisier
Ratio of Variances:
November SST
Thermocline pattern much noisier
Similar patterns with differences throughout tropics and subtropics
Ratio of Variances:
November Thermocline

23. What is driving these differences?
Differences are confined to the tropics and subtropics, little systematic difference in extratropics
True for both May and November starts (not shown)
Not being driven by ‘weather noise’
Scale dependent noise focused on the tropics
Precipitation?

24. Ratio of Ensemble Variance: T1279 / T319 Precipitation
May Values (May Initial Conditions)

25. Ratio of Ensemble Variance: T1279 / T319 Precipitation
June Values (May Initial Conditions)

26. Ratio of Ensemble Variance: T1279 / T319 Precipitation
July Values (May Initial Conditions)

27. Ratio of Ensemble Variance: T1279 / T319 Precipitation
August Values (May Initial Conditions)

28. Ratio of Ensemble Variance: T1279 / T319 Precipitation
September Values (May Initial Conditions)

29. Ratio of Ensemble Variance: T1279 / T319 Precipitation
October Values (May Initial Conditions)

30. Ratio of Ensemble Variance: T1279 / T319 Precipitation
November Values (May Initial Conditions)

31. Summary and Conclusions
Ensemble mean SST bias relatively insensitive to increased resolution
Ensemble variance in tropics and subtropics increases significantly from T319 to T639
Effect spans multiple ocean levels (SST, Thermocline Depth)
Tropical/Subtropical focus, resolution dependence, suggests role of convection
Pattern of precipitation variance increase consistent with ocean patterns
Ensemble variance does not increase significantly from T639 to T1279
Consistent with step-change between T159 and T511 in Athena simulations
Critical threshold between T319 and T639?

32. Meeting Logistics Dinner! Tomorrow
For those attending dinner, reservation is at 6:30pm. Let me know if you need a ride.
Tomorrow
Breakfast, lunch and break schedule as today
Discussion sessions to cover:
Summary of Day 1 results
Further analysis to be performed
Initial publications and writing responsibilities
Further experiments to be performed

33. SSTA Spread/RMSE (May ICs 1982-2011)
- Leading 7 Months