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A Subgrid Orography Scheme: Ready for Prime Time

A Subgrid Orography Scheme: Ready for Prime Time. 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. Subgrid scheme.

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A Subgrid Orography Scheme: Ready for Prime Time

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  1. A Subgrid Orography Scheme:Ready for Prime Time 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 • Developmental branch updated to cam3.2.41 • 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 to within 0.01 Wm-2 • Load balancing within nodes for both dycores • Load balancing between nodes for both dycores (IJHPCA, 2005) • Runoff distributed according to elevation of river transport model surface elevation • AMIP simulations at T42 and 2˚x2.5º resolution • Detailed evaluation in eight regions (J. Climate, 2006a) • IPCC A1B simulation 1977-2100 at 2˚x2.5˚ resolution (J. Climate, 2006b)

  6. Experiments • AMIP SST • Initialize September 1977 • Run through 1989 • T42 • TOPOG 11 elevation classes • No TOPOG • 2x2.5 • TOPOG 11 elevation classes • No TOPOG • 1x1.25 • No TOPOG • IPCC A1B • 2x2.5 • TOPOG 11 elevation classes • 1977-2100

  7. Evaluation

  8. temperature

  9. March Snow

  10. Precipitation in other regions

  11. Does the Scheme Impact the Grid Cell Mean Climate? Precipitation at 2x2.5 resolution

  12. Surface Air Temperature 2x2.5

  13. Zonal and Annual Mean

  14. Planetary Energy Balance

  15. Global Annual Mean

  16. Computational Burden

  17. Zonal Mean Burden

  18. 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

  19. Summary • The subgrid scheme provides valuable regional detail at a modest computational cost. • It produces some biases, largely due to neglect of rainshadow. • Its biases can be ameliorated by reducing grid size to 50-100 km. • It produces little impact on grid cell means of most fields, except for snow water. • It can be treated as an option with minimal retuning.

  20. Future Work • Update to support CCSM and hi-res CLM: • pass elevation class fields through the coupler • optional online mapping of atmosphere fields to CLM grid • Present to LMWG for approval. • Submit proposal to SSC. • Merge on to developmental trunk. • Continue to maintain as CCSM changes.

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