Workshop on Tropical Biases, 28 May 2003
CCSM CAM2 Tropical Simulation CCSM CAM2 Tropical Simulation
James J. HackJames J. Hack
National Center for Atmospheric Research National Center for Atmospheric Research Boulder, Colorado USABoulder, Colorado USA
Collaborators: Julie M. CaronJohn E. Truesdale
Workshop on Tropical Biases, 28 May 2003
CAM2 FormulationCAM2 Formulation
Significant changes to components in hydrological Significant changes to components in hydrological cyclecycle
• 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 In many ways, the tropical simulation is very similar to CCM3to CCM3
Workshop on Tropical Biases, 28 May 2003
Diabatic Forcing of the Deep TropicsDiabatic Forcing of the Deep Tropics
CAM2
Workshop on Tropical Biases, 28 May 2003
Diabatic Forcing of the Deep TropicsDiabatic Forcing of the Deep Tropics
CAM2
CAM2
Workshop on Tropical Biases, 28 May 2003
CAM2 Simulation of Tropical ClimateCAM2 Simulation of Tropical ClimateMixed bag with respect to CCM3 and observationsMixed 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 simulationImpact 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
Workshop on Tropical Biases, 28 May 2003
Precipitable WaterPrecipitable WaterCAM2 CCM3
CAM2 - NVAP CCM3 - NVAP
Workshop on Tropical Biases, 28 May 2003
Precipitable WaterPrecipitable Water
CAM2
CCM3
CAM2 - CCM3
Workshop on Tropical Biases, 28 May 2003
Moist Stability (western Pacific)Moist Stability (western Pacific)
CAM2CCM3
RAOBS
Workshop on Tropical Biases, 28 May 2003
Precipitation RatePrecipitation RateCCM3
CCM3 - Xie-Arkin
CAM2
CAM2 - Xie-Arkin
Workshop on Tropical Biases, 28 May 2003
Surface Absorbed Solar FluxSurface Absorbed Solar FluxCAM2
CCM3
CAM2 - CCM3
Workshop on Tropical Biases, 28 May 2003
Surface Stress (low level dynamical Surface Stress (low level dynamical circulation)circulation)
CAM2
CAM2 - ERS
Workshop on Tropical Biases, 28 May 2003
Tropical Variability: Madden-Julian Tropical Variability: Madden-Julian OscillationOscillation
Workshop on Tropical Biases, 28 May 2003
Tropical Variability: MJO IndexTropical Variability: MJO Index
Workshop on Tropical Biases, 28 May 2003
Steps forward?Steps forward?
Investigations of missing/incomplete processesInvestigations of missing/incomplete processes convective momentum transport as an example
Investigation of the role of horizontal/vertical Investigation of the role of horizontal/vertical
resolutionresolution climate models appear to be stuck at the 200-300 km x range
what are the issues/benefits associated with higher resolution?
Workshop on Tropical Biases, 28 May 2003
Held Eddy Diffusivity Enhancement Held Eddy Diffusivity Enhancement ExperimentExperiment
Simple linear function of cumulus mass fluxSimple linear function of cumulus mass flux• D = c • f ( Mc )
– experiment 1, c= 2– experiment 2, c=10
Workshop on Tropical Biases, 28 May 2003
Held cumulus friction experimentHeld cumulus friction experiment
Workshop on Tropical Biases, 28 May 2003
Held cumulus friction experimentHeld cumulus friction experiment
Workshop on Tropical Biases, 28 May 2003
Held cumulus friction experimentHeld cumulus friction experiment
Workshop on Tropical Biases, 28 May 2003
Tropical Variability: MJO Index (cumulus Tropical Variability: MJO Index (cumulus friction)friction)
Workshop on Tropical Biases, 28 May 2003
Cumulus momentum transportCumulus momentum transport
• example of a clear simulation sensitivity example 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
Workshop on Tropical Biases, 28 May 2003
Resolution??Resolution??
The CCM/CAM has used a T42 truncation for nearly a The CCM/CAM has used a T42 truncation for nearly a decadedecade
• 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 There is no question that increased resolution results in systematically better simulation results across a wide range of systematically better simulation results across a wide range of metricsmetrics
Workshop on Tropical Biases, 28 May 2003
Eastern Pacific Surface StressEastern Pacific Surface Stress
T42 AnomalyT42 Anomaly
Workshop on Tropical Biases, 28 May 2003
Eastern Pacific Surface StressEastern Pacific Surface Stress
T85 mountains T42 mountains
Workshop on Tropical Biases, 28 May 2003
Eastern Pacific Surface StressEastern Pacific Surface Stress
T85 T42
Workshop on Tropical Biases, 28 May 2003
High-resolution global climate simulationsHigh-resolution global climate simulations
Another practical and immediate problemAnother 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
T85Cloud parameterization doesn’t scale!
OBS
T85
Workshop on Tropical Biases, 28 May 2003
High-resolution global climate simulationsHigh-resolution global climate simulations
Question:Question:
How does the behavior of parameterized processes change with resolution?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
Workshop on Tropical Biases, 28 May 2003
Simulation Improvements in Mean MeasuresSimulation Improvements in Mean Measures
high-resolution
standard
Workshop on Tropical Biases, 28 May 2003
Simulation Improvements in Mean MeasuresSimulation Improvements in Mean Measures
CAM-CRM
Intriguing results from imbedded CRM simulations
Khairoutdinov and Randall
(2003)
Workshop on Tropical Biases, 28 May 2003
Cumulus Parameterization as an Cumulus Parameterization as an ExampleExample
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?
Workshop on Tropical Biases, 28 May 2003
Spectral characteristics of middle atmospheric time Spectral characteristics of middle atmospheric time seriesseries
Averaged up to T42
Workshop on Tropical Biases, 28 May 2003
High-resolution global climate simulationsHigh-resolution global climate simulationsResponse of Deep Tropics as function of resolutionResponse of Deep Tropics as function of resolution
Workshop on Tropical Biases, 28 May 2003
High-resolution global climate simulationsHigh-resolution global climate simulationsIdealized Response of Deep Tropics as function of resolutionIdealized Response of Deep Tropics as function of resolution
Workshop on Tropical Biases, 28 May 2003
Tropical Variability: Madden-Julian Tropical Variability: Madden-Julian OscillationOscillation
T85
Workshop on Tropical Biases, 28 May 2003
SummarySummary
• 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
Workshop on Tropical Biases, 28 May 2003
The End
Workshop on Tropical Biases, 28 May 2003
Warm Pool L.S. Temperature Forcing Time Warm Pool L.S. Temperature Forcing Time Series Series
