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Ensemble Spread and Resolution in Minerva Simulations

Ensemble Spread and Resolution in Minerva Simulations. Ben Cash and Jieshun Zhu Minerva Project Team Minerva Workshop, GMU/ COLA, September 16, 2013. Role of Resolution in Minerva Simulations. Significant Differences in Atmosphere, Ocean Components Multiple atmosphere resolutions

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Ensemble Spread and Resolution in Minerva Simulations

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  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 2000-2011 May Values (May Initial Conditions)

  5. Ratio of Ensemble Variance: T639 / T319 SST 2000-2011 June Values (May Initial Conditions)

  6. Ratio of Ensemble Variance: T639 / T319 SST 2000-2011 July Values (May Initial Conditions)

  7. Ratio of Ensemble Variance: T639 / T319 SST 2000-2011 August Values (May Initial Conditions)

  8. Ratio of Ensemble Variance: T639 / T319 SST 2000-2011 September Values (May Initial Conditions)

  9. Ratio of Ensemble Variance: T639 / T319 SST 2000-2011 October Values (May Initial Conditions)

  10. Ratio of Ensemble Variance: T639 / T319 SST 2000-2011 November Values (May Initial Conditions)

  11. Intra-ensemble variance of SST increases significantly from T319 to T639 • Increase focused primarily in the tropics and subtropics • Result insensitive to choice of 2000-2011 period or 1980-2011 (not shown) • What about T639 to T1279?

  12. Ratio of Ensemble Variance: T1279 / T639 SST 2000-2011 November Values (May Initial Conditions)

  13. 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?

  14. Ratio of Ensemble Variance: T639 / T319 Thermocline Depth 2000-2011 May Values (May Initial Conditions)

  15. Ratio of Ensemble Variance: T1279 / T639 Thermocline Depth 2000-2011 June Values (May Initial Conditions)

  16. Ratio of Ensemble Variance: T1279 / T639 Thermocline Depth 2000-2011 July Values (May Initial Conditions)

  17. Ratio of Ensemble Variance: T1279 / T639 Thermocline Depth 2000-2011 August Values (May Initial Conditions)

  18. Ratio of Ensemble Variance: T1279 / T639 Thermocline Depth 2000-2011 September Values (May Initial Conditions)

  19. Ratio of Ensemble Variance: T1279 / T639 Thermocline Depth 2000-2011 October Values (May Initial Conditions)

  20. Ratio of Ensemble Variance: T1279 / T639 Thermocline Depth 2000-2011 November Values (May Initial Conditions)

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

  22. 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?

  23. Ratio of Ensemble Variance: T1279 / T319 Precipitation 2000-2011 May Values (May Initial Conditions)

  24. Ratio of Ensemble Variance: T1279 / T319 Precipitation 2000-2011 June Values (May Initial Conditions)

  25. Ratio of Ensemble Variance: T1279 / T319 Precipitation 2000-2011 July Values (May Initial Conditions)

  26. Ratio of Ensemble Variance: T1279 / T319 Precipitation 2000-2011 August Values (May Initial Conditions)

  27. Ratio of Ensemble Variance: T1279 / T319 Precipitation 2000-2011 September Values (May Initial Conditions)

  28. Ratio of Ensemble Variance: T1279 / T319 Precipitation 2000-2011 October Values (May Initial Conditions)

  29. Ratio of Ensemble Variance: T1279 / T319 Precipitation 2000-2011 November Values (May Initial Conditions)

  30. 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?

  31. Meeting Logistics • Dinner! • 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

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

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