1. Update on CAM2.X Development and Future Research Directions
J. J. Hack
National Center for Atmospheric Research
Boulder, Colorado USA
On behalf of
Phil Rasch and Leo Donner, CCSM AMWG Co-Chairs

2. Outline Model biases in CAM2 Physics changes in CAM 2.X
Simulation improvements in CAM 2.X
Future directions

3. Principal CAM2/CCSM2 Biases
Warm winter land surface temperature bias
Cold tropical tropopause temperatures
Double ITCZ and extended cold tongue
Erroneous cloud response to SST changes
Deficiencies in E. Pacific surface energy budget
Underestimation of tropical variability
All work over last year aimed at reducing these biases

4. CAM 2.X Physics Changes Relative to CAM2
Moist Physics and Clouds
improved prognostic cloud water & moist processes
tighter interaction of shallow convection and cloud water
transfer of mixed phase precipitation to land surface
improved cloud parameterization
Radiation
shortwave forcing by diagnostic aerosols
updated SW scheme for H2O absorption
updated LW scheme for LW absorption and emission
Modeling Extensions
reintroduction of Slab Ocean Model (SOM)
Other
energy fixers for dynamical cores plus related diagnostics
additional diagnostic capabilities
updated boundary datasets
implementation improvements
high-resolution configuration

5. Examples of Simulation Improvements:
NH Winter Land Surface Temperatures

6. Examples of Simulation Improvements:
Tropopause Temperatures

7. Examples of Simulation Improvements:
Shortwave Response to ENSO
CAM2
CAM2.X
ERBE (ERBS)

8. Notable Simulation Changes:
Surface Insolation Changes (primarily aerosol effects)
CAM2.X
CAM2
CAM2.X-CAM2
CAM2.X - CAM2

9. High-resolution configurations
T85 spectral Eulerian configuration
workhorse for IPCC
2x2.5° Finite-Volume configuration
in process
High-resolution simulation improvements
warmer tropospheric temperatures
improvements in low-level circulation

10. T85 Zonal Annual Mean Temperatures
CAM2.X T85
CAM2.X T42
CAM2.X T85-CAM2.X T42

11. T85 vs T42 Cloud Forcing
T85 vs T42

12. T85 Surface Wind Stress
T85
T42
Diff

13. Current Assessment of High-Resolution Coupled Simulation (oceanographer’s perspective)
reductions in warm biases off the western coasts of the continents
reductions in southern ocean SST errors
improvements in the near equatorial upper-ocean temperature structures
improved semi-annual signal of equatorial Pacific SSTs
improved Pacific equatorial undercurrent (increased westward wind stress)
improved surface salinity changes in the Arctic
poleward shift of southern hemisphere storm track

14. Future Directions Return to science-driven investment
understanding, improving, and evaluating key processes in physical climate system
attack problems from a fundamental perspective
holistic focus on phenomenology that deals with nonlinear interactions of processes
accept incremental improvements based on fundamental process advancements
focus on developing a better understanding of simulation performance
evaluation of climate sensitivity, feedbacks, forcing, etc.
identify and fill holes in existing expertise for dedicated attention
boundary layer, cloud/aerosol microphysics, numerical methods
Coordinate research activities on physical climate system with activities that extend simulation capabilities
examples include aerosol, chemical, and biogeochemical modeling extensions

15. Future Directions (continued)
Extensions to modeling capabilities
Aerosol modeling
enhance/strengthen focused effort
aerosol chemistry, links to cloud microphysics (e.g., indirect effect), atmospheric chemistry
constrain process models and associated physical parameterization development
Atmospheric chemistry
enhance/strengthen ongoing efforts
e.g., interactions with ACD and external collaborators
revived CCSM working group?
quantify requirements and constraints on development of the physical climate system
Integration of offline transport modeling capability
replace MOZART and MATCH

16. Future Directions (continued)
Extensions to modeling capabilities
Middle-Atmosphere and Climate (middle atmospheric dynamics/physics)
continued development of WACCM
Upper Troposphere Lower Stratosphere (UTLS) modeling initiative
emphasis on water transport/interactions
immediate driver on development of improved numerical approximations
Biogeochemistry
support and leverage division and external efforts on carbon cycle modeling
stress treatment of boundary-layer and convective-scale transport mechanisms
e.g., mineral dust
leverage links to atmospheric chemical modeling
interactive surface processes including chemical interactions

17. Future Directions (continued)
Where would we like to be in 5 years?
highly-integrated physical parameterization package
boundary layer - moist convection - stratiform cloud processes
explore tighter linkages available w/ regard to radiation and clouds?
significantly enhanced large-scale dynamical driver(s)
2-3X increase in default horizontal resolution in each dimension
improved vertical resolution as dictated by physics, dynamics, or numerics
e.g., boundary layer, resolution of tropopause height
capability for local resolution refinement
incorporation of adaptive gridding techniques?
formally conservative transport capabilities
isentropic formulation(s)?
isotropic discretizations in spherical geometry?
non-hydrostatic formulations??
is this essential to scientific work on the proposed time scale?

18. Future Directions (continued)
Where would we like to be in 5 years?
fully-interactive aerosol modeling capabilities
links to cloud microphysics to accommodate work on indirect effect
fully interactive atmospheric chemical modeling capability
stratospheric and tropospheric formulations
necessary hooks/linkages to biogeochemical cycles
be creating hierarchy of modeling tools along the way
simplified column physics frameworks through fully-coupled system model
provides a powerful diagnostic and evaluation framework for understanding
be exploiting opportunities w/ regard to assimilation capabilities
CAPT parameterization evaluation framework
development of relationships with NASA; NCEP, others?

19. Summary
CAM2.X model driven by need to reduce some major systematic biases
Incorporates major changes to parameterized physics
Incorporates extensions to modeling and diagnostic capabilities
High-resolution configuration shows promising behavior
Strong foundation to build upon

20. END

21. Other Notable Simulation Features:
Large differences in cloud amount
CAM2.X
CAM2
CAM2.X-CAM2

22. Extension to Include Convective Cloud Fraction
Some improvements to cloud distribution and associated SWCF
Clear improvements in short wave radiative response to ENSO

23. Other Notable Simulation Features:
Large differences in cloud condensate
CAM2.X
CAM2
CAM2.X-CAM2

24. 2nd backup

25. Example of extensions to cloud scheme
Majority of CAM clouds are diagnosed as a function of relative humidity
stratocumulus cloud coverage diagnosed from Klein-Hartmann stability metric
generally limited to small areas in the eastern portion of ocean basins
remainder of cloud relative humidity dependent
moisture biases contributed to bi-modal vertical distribution of cloud
CCM3 included a cloud diagnosis based on convective mass flux
formulation employed average cloud mass flux in convective layer
vertical distribution based on random overlap assumption

26. Convective Cloud Fraction
Introduce cloud diagnostic based on local convective mass flux
cloud fraction logarithmic function of cloud mass flux

27. Convective Cloud Fraction

28. Convective Cloud Fraction
Some improvements to cloud distribution and associated SWCF
Clear improvements in short wave radiative response to ENSO

29. Second change motivated by problems with physics package at high resolution and in FV dynamical core
Inability to maintain extratropical cloud forcing at high resolution
Similar problems with cloud forcing using finite-volume dynamical core
T42
T42
T85
T85

30. Standard Physics Tuning Implications
Implied ocean heat transport
T85 vs T42

31. T85 - T42 Temperature Simulation
Deficiencies in extratropical cloud forcing fundamentally related to deficiencies in cloud fraction scheme (relative humidity clouds)
T85 - T42 Temperature Simulation

32. Provide additional source of cloud liquid water from “shallow convection” process
Shallow convection scheme designed to deal with shallow and mid-level instabilities
philosophical framework based on redistribution of water, as opposed to rainout
Applied as “cleanup procedure” following application of deep convection
Detrainment into unsaturated environment
Condensation/rainout layer

33. Detrainment of cloud liquid water to prognostic clouds from shallow convection
Explicitly calculate the minimum rainwater autoconversion
drizzle rates in trade cumulus regimes; little change to behavior
2-3 mm/day rainfall rates in deep convective regimes
Detrain remainder of required condensation to cloud water scheme
provides sufficient additional degree of freedom allowing scaling of cloud scheme
enables a more portable physics package across dynamical cores

34. Enhanced Physics Cloud Forcing (intermediate result)
T85 vs T42

35. Current Assessment of High-Resolution Coupled Simulation (oceanographer’s perspective)
reductions in the warm biases off the western coasts of the continents
enhanced upwelling in the eastern oceans
reductions in southern ocean SST errors
improvements in the near equatorial upper-ocean temperature structures
improved semi-annual signal of equatorial Pacific SSTs
improved Pacific equatorial undercurrent due to increased westward wind stress
improved surface salinity changes in the Arctic
poleward shift of southern hemisphere storm track