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CCSM CAM2 Tropical Simulation

CCSM CAM2 Tropical Simulation. James J. Hack National Center for Atmospheric Research Boulder, Colorado USA. Collaborators: Julie M. Caron John E. Truesdale. CAM2 Formulation. Significant changes to components in hydrological cycle Clouds prognostic formulation

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CCSM CAM2 Tropical Simulation

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

  2. CAM2 Formulation Significant changes to components in hydrological cycle • Clouds • prognostic formulation • generalized cloud overlap treatment • Radiation • longwave water vapor absorption formulation • Convection • evaporation of precipitation mechanism In many ways, the tropical simulation is very similar to CCM3

  3. Diabatic Forcing of the Deep Tropics CAM2

  4. Diabatic Forcing of the Deep Tropics  CAM2 CAM2

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

  6. Precipitable Water CAM2 CCM3 CCM3 - NVAP CAM2 - NVAP

  7. Precipitable Water CAM2 CCM3 CAM2 - CCM3

  8. Moist Stability (western Pacific) CAM2 CCM3 RAOBS

  9. Precipitation Rate CCM3 CAM2 CCM3 - Xie-Arkin CAM2 - Xie-Arkin

  10. Surface Absorbed Solar Flux CAM2 CCM3 CAM2 - CCM3

  11. Surface Stress (low level dynamical circulation) CAM2 CAM2 - ERS

  12. Tropical Variability: Madden-Julian Oscillation

  13. Tropical Variability: MJO Index

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

  15. Held Eddy Diffusivity Enhancement Experiment Simple linear function of cumulus mass flux • D = c • f ( Mc ) • experiment 1, c= 2 • experiment 2, c=10

  16. Held cumulus friction experiment

  17. Held cumulus friction experiment

  18. Held cumulus friction experiment

  19. Tropical Variability: MJO Index (cumulus friction)

  20. Cumulus momentum transport • example of a clear simulation sensitivity • response is not unique! • what is compensating for absence of this process? • example of process-specific feature in parameterizations • lends itself to systematic investigation

  21. Resolution?? The CCM/CAM has used a T42 truncation for nearly a decade • systematic biases related to resolution in any way? • double ITZC • eastern ocean upwelling • experimentation 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. Eastern Pacific Surface Stress T42 Anomaly

  23. Eastern Pacific Surface Stress T85 mountains T42 mountains

  24. Eastern Pacific Surface Stress T85 T42

  25. T85 OBS T42 T85 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 Cloud parameterization doesn’t scale!

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

  27. Simulation Improvements in Mean Measures high-resolution standard

  28. Intriguing results from imbedded CRM simulations Khairoutdinov and Randall (2003) CAM-CRM Simulation Improvements in Mean Measures

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

  30. Spectral characteristics of middle atmospheric time series Averaged up to T42

  31. High-resolution global climate simulations Response of Deep Tropics as function of resolution

  32. High-resolution global climate simulations Idealized Response of Deep Tropics as function of resolution

  33. T85 Tropical Variability: Madden-Julian Oscillation

  34. Summary • Continue 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 biases • seems contingent on hypothesis-driven process-oriented investigations • “system” approach • need to be exploring the adequacy of “climate modeling” resolution

  35. The End

  36. Warm Pool L.S. Temperature Forcing Time Series

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