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

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

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

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

Examples of Simulation Improvements: NH Winter Land Surface Temperatures

Examples of Simulation Improvements: Tropopause Temperatures

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

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

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

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

T85 vs T42 Cloud Forcing T85 vs T42

T85 Surface Wind Stress T85 T42 Diff

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

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

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

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

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?

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?

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

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

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

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

2nd backup

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

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

Convective Cloud Fraction

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

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

Standard Physics Tuning Implications Implied ocean heat transport T85 vs T42

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

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

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

Enhanced Physics Cloud Forcing (intermediate result) T85 vs T42

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