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Application of a Subgrid Orography Scheme to CAM and CLM

Application of a Subgrid Orography Scheme to CAM and CLM. Steven Ghan and Tim Shippert Pacific Northwest National Lab. Ghan, S. J., X. Bian, A. G. Hunt, and A. Coleman, 2002: The thermodynamic influence of subgrid orography in a global climate model, Climate Dynamics , 20 , 31-44.

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Application of a Subgrid Orography Scheme to CAM and CLM

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  1. Application of a Subgrid Orography Scheme to CAM and CLM Steven Ghan and Tim Shippert Pacific Northwest National Lab Ghan, S. J., X. Bian, A. G. Hunt, and A. Coleman, 2002: The thermodynamic influence of subgrid orography in a global climate model, Climate Dynamics, 20, 31-44.

  2. Subgrid scheme

  3. Implementation • Applies to all column physics • clouds • radiative transfer • vertical mixing • surface physics

  4. Elevation Classification

  5. Progress • Scheme applied to CAM and CLM • Euler dycore • Finite-volume dycore (1-D and 2-D domain decomposition) • Developmental branch updated to cam2_0_2_dev55 (IPCC physics) • Bit-for-bit agreement between SP, SMP, SPMD • Restarts bit-for-bit agreement • Bit-for-bit agreement with dev trunk if subgrid scheme turned off • Energy conservation demonstrated* • Load balancing within nodes for both dycores • Load balancing between nodes for both dycores (FV 1-D only) • Runoff distributed according to elevation of river transport model surface elevation

  6. Experiments • AMIP SST • Initialize September 1977 • T42 • TOPOG run through 1983 • No TOPOG data taken from cam2_0_2_dev61_climo • 2x2.5 • TOPOG run through 1989 • No TOPOG run through 1989

  7. Evaluation

  8. temperature

  9. March snow

  10. Does the Scheme Impact the Grid Cell Mean Climate?

  11. The subgrid scheme changes the large-scale climate significantly for the FV dycore, but not the EUL dycore.

  12. Planetary Energy Balance

  13. Global Annual Mean

  14. What is Causing the FV Problem?

  15. Divergence of T and ST

  16. Computational Burden

  17. Zonal Mean Burden

  18. Global Burden

  19. Balancing the Load • Distribute elevation classes across physics chunks • Rank grid cells according to number of classes • Starting with cells with most classes, assign all classes in cell to the chunk with the least number of columns • Continue distribution until classes for all cells have been assigned to chunks • Save cell index and area corresponding to each chunk column • Distribute chunks across nodes • -Minimize dynamic-physics transpose cost by assigning chunks to node withmost dynamics grid cells from chunk • -fraction of columns assigned to same node as dynamics: 40% for T42 11 classes on 8 nodes

  20. Load Balancing Performance

  21. Code Changes • Unlike any other parameterization • All column physics applied to each elevation class • Mostly manifest at higher levels • phys_grid phys_grid_init create_chunks scatter_field_to_chunk gather_chunk_to_field • phys_types • dp_coupling • history

  22. Future Work • Extend the T42 subgrid run and run control for comparison. • Correct the FV energy imbalance and rerun FV 2x2.5. • Apply load balancing to the finite-volume implementation of the scheme, for 2D domain decomposition. • Present to CCSM LMWG for approval. • Submit proposal to CAM code review board. • Check in as permanent CAM and CLM option. • Perform simulations at higher resolution with subgrid scheme. • Perform IPCC simulations with CAM using the subgrid scheme and ocean surface conditions from CCSM simulations without the subgrid scheme. • Adapt the scheme to CCSM. • Continue to update as CCSM changes.

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