1. Workshop on Tropical Biases, 28 May 2003 CCSM CAM2 Tropical Simulation James J. Hack National Center for Atmospheric Research Boulder, Colorado USA Collaborators: Julie M. Caron John E. Truesdale

2. Workshop on Tropical Biases, 28 May 2003 CAM2 Formulation Significant changes to components in hydrological cycle CloudsClouds –prognostic formulation –generalized cloud overlap treatment RadiationRadiation –longwave water vapor absorption formulation ConvectionConvection –evaporation of precipitation mechanism In many ways, the tropical simulation is very similar to CCM3

3. Workshop on Tropical Biases, 28 May 2003 Diabatic Forcing of the Deep Tropics CAM2

4. Workshop on Tropical Biases, 28 May 2003 Diabatic Forcing of the Deep Tropics  CAM2

5. Workshop on Tropical Biases, 28 May 2003 CAM2 Simulation of Tropical Climate Mixed bag with respect to CCM3 and observations Atmospheric stateAtmospheric state –cold, but improved moisture Precipitable water distributionPrecipitable water distribution –tropical west Pacific significantly improved, tropical Atlantic still problematical Precipitation distributionPrecipitation distribution –tropical east Pacific significantly improved –greater tendency to produce double ITCZ in Pacific and Indian Oceans Eastern ocean solar energy budgetEastern ocean solar energy budget –large reductions in surface absorbed solar radiation in stratus regimes –comparable compensation in other terms of surface energy balance VariabilityVariability –continues to be very weak with respect to observations Impact on coupled simulation Biases further amplified in coupled frameworkBiases further amplified in coupled framework –e.g., double ITCZ Improvements produce little or no response in coupled systemImprovements produce little or no response in coupled system –e.g., eastern ocean SST biases

6. Workshop on Tropical Biases, 28 May 2003 Precipitable Water Precipitable Water CAM2CCM3 CAM2 - NVAP CCM3 - NVAP

7. Workshop on Tropical Biases, 28 May 2003 Precipitable Water Precipitable Water CAM2 CCM3 CAM2 - CCM3

8. Workshop on Tropical Biases, 28 May 2003 Moist Stability (western Pacific) Moist Stability (western Pacific) CAM2 CCM3 RAOBS

9. Workshop on Tropical Biases, 28 May 2003 Precipitation Rate Precipitation Rate CCM3 CCM3 - Xie-Arkin CAM2 CAM2 - Xie-Arkin

10. Workshop on Tropical Biases, 28 May 2003 Surface Absorbed Solar Flux Surface Absorbed Solar Flux CAM2 CCM3 CAM2 - CCM3

11. Workshop on Tropical Biases, 28 May 2003 Surface Stress (low level dynamical circulation) CAM2 CAM2 - ERS

12. Workshop on Tropical Biases, 28 May 2003 Tropical Variability: Madden-Julian Oscillation

13. Workshop on Tropical Biases, 28 May 2003 Tropical Variability: MJO Index

14. Workshop on Tropical Biases, 28 May 2003 Steps forward? Investigations of missing/incomplete processes l l convective momentum transport as an example Investigation of the role of horizontal/vertical resolution l l climate models appear to be stuck at the 200-300 km  x range l l what are the issues/benefits associated with higher resolution?

15. Workshop on Tropical Biases, 28 May 2003 Held Eddy Diffusivity Enhancement Experiment Simple linear function of cumulus mass flux D = c f ( M c ) –experiment 1, c= 2 –experiment 2, c=10

16. Workshop on Tropical Biases, 28 May 2003 Held cumulus friction experiment

17. Workshop on Tropical Biases, 28 May 2003 Held cumulus friction experiment

18. Workshop on Tropical Biases, 28 May 2003 Held cumulus friction experiment

19. Workshop on Tropical Biases, 28 May 2003 Tropical Variability: MJO Index (cumulus friction)

20. Workshop on Tropical Biases, 28 May 2003 Cumulus momentum transport example of a clear simulation sensitivityexample of a clear simulation sensitivity –response is not unique! –what is compensating for absence of this process? example of process-specific feature in parameterizationsexample of process-specific feature in parameterizations –lends itself to systematic investigation

21. Workshop on Tropical Biases, 28 May 2003 Resolution?? The CCM/CAM has used a T42 truncation for nearly a decade systematic biases related to resolution in any way?systematic biases related to resolution in any way? –double ITZC –eastern ocean upwelling experimentation at T85/T170 underway to address role of resolutionexperimentation at T85/T170 underway to address role of resolution –uncoupled simulations and coupled simulations –idealized simulations There is no question that increased resolution results in systematically better simulation results across a wide range of metrics

22. Workshop on Tropical Biases, 28 May 2003 Eastern Pacific Surface Stress Eastern Pacific Surface Stress T42 Anomaly

23. Workshop on Tropical Biases, 28 May 2003 Eastern Pacific Surface Stress Eastern Pacific Surface Stress T85 mountainsT42 mountains

24. Workshop on Tropical Biases, 28 May 2003 Eastern Pacific Surface Stress Eastern Pacific Surface Stress T85T42

25. Workshop on Tropical Biases, 28 May 2003 High-resolution global climate simulations Another practical and immediate problem Configure high-resolution version of CCSM CAM for global change simulations –lead to improved simulations on regional scales? –requires that behavior of parameterized processes scale to higher-resolutions T42 T85 Cloud parameterization doesn’t scale! OBS T85

26. Workshop on Tropical Biases, 28 May 2003 High-resolution global climate simulations Question: How does the behavior of parameterized processes change with resolution? Williamson, Kiehl, and Hack (1995) Changes in dynamical circulation properties as a function of resolution

27. Workshop on Tropical Biases, 28 May 2003 Simulation Improvements in Mean Measures high- resolution standard

28. Workshop on Tropical Biases, 28 May 2003 Simulation Improvements in Mean Measures CAM-CRM Intriguing results from imbedded CRM simulations Khairoutdinov and Randall (2003)

29. Workshop on Tropical Biases, 28 May 2003 Cumulus Parameterization as an Example we resolve the “large scale” and parameterize the unresolved scales What happens to the “large-scale” forcing on the parameterized physics as resolution is increased?

30. Workshop on Tropical Biases, 28 May 2003 Spectral characteristics of middle atmospheric time series Averaged up to T42

31. Workshop on Tropical Biases, 28 May 2003 High-resolution global climate simulations Response of Deep Tropics as function of resolution

32. Workshop on Tropical Biases, 28 May 2003 High-resolution global climate simulations Idealized Response of Deep Tropics as function of resolution

33. Workshop on Tropical Biases, 28 May 2003 Tropical Variability: Madden-Julian Oscillation T85

34. Workshop on Tropical Biases, 28 May 2003 Summary Continue to wrestle with longstanding systematic tropical biasesContinue to wrestle with longstanding systematic tropical biases –common to many global models of the climate system –present despite demonstrable improvements to model formulation –present despite demonstrable improvements to other simulation features Progress toward addressing these biasesProgress toward addressing these biases –seems contingent on hypothesis-driven process-oriented investigations –“system” approach –need to be exploring the adequacy of “climate modeling” resolution

35. Workshop on Tropical Biases, 28 May 2003 The End

36. Workshop on Tropical Biases, 28 May 2003 Warm Pool L.S. Temperature Forcing Time Series