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Expanding Regridding Capabilities of the Earth System Modeling Framework

Expanding Regridding Capabilities of the Earth System Modeling Framework. Andrew Scholbrock University of Colorado – Boulder Robert Oehmke NOAA/CIRES. Outline. Introduction Background Information Incorporating LibCF Regridding into ESMF Current Status Future Work. Introduction.

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Expanding Regridding Capabilities of the Earth System Modeling Framework

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  1. Expanding Regridding Capabilities of the Earth System Modeling Framework Andrew Scholbrock University of Colorado – Boulder Robert Oehmke NOAA/CIRES

  2. Outline • Introduction • Background Information • Incorporating LibCF Regridding into ESMF • Current Status • Future Work

  3. Introduction • This project aims to allow regridding software that follows a proposed metadata standard (Gridspec) to be used within the Earth System Modeling Framework (ESMF) • As new regridding capabilities are developed they will be automatically available through ESMF

  4. ESMF • Framework developed by a multi-agency consortium [1] • Provides standard interfaces for model components • Provides standard structure for transferring data between model components • Provides a range of utilities to ease coupling • Data regridding • Data redistribution • Time management • Error handling

  5. Gridspec • Metadata convention developed at NOAA GFDL [2] • Proposed for inclusion in the Climate and Forecast (CF) [3] conventions • Gridspec represents grids as mosaics and tiles • Mosaic files contain a list of tile files and how they are connected • Tile files contain actual grid coordinate information http://www.gfdl.noaa.gov/~vb/gridstd/gridstdse2.html#x4-160002.7

  6. LibCF • Utility library developed at Unidata • Built on top of NetCDF [4] Climate and Forecast (CF) conventions • LibCF [3] includes the capability to: • Manipulate Gridspec metadata on a NetCDF file • Create Gridspec files • Regrid between different Gridspec files • LibCF is still in alpha release mode

  7. Regridding Overview • Climate and other models require coupling of modeling components (e.g. atmosphere, ocean) • Different modeling components may require different grids • e.g. different shapes or different resolutions • Regridding needs to be performed to move data between components on different grids • Steps involved in regridding: • Generate interpolation weights • Apply weights to interpolate field using a sparse matrix multiply

  8. ESMF Regridding • Methods of accessing regridding: • Online • Subroutine calls which calculate weights during a model run • Can get weights or feed directly into ESMF sparse matrix multiply • Offline • Application which generates a netCDF interpolation weight file from two netCDF grid files • Computation of weights can be done in parallel • Supported grids: • 2D meshes composed of triangles or quadrilaterals • 3D meshes composed of hexahedra • 2D/3D logically rectangular grids • Cubed sphere • Supported interpolation methods: • Bilinear • Higher order finite element patch recovery [5][6] • Conservative (beta version) • Not all combinations of the above are supported

  9. LibCF Regridding • LibCF takes Gridspec files and field data files as input to generate weights and interpolate data • If just Gridspec files are specified then only interpolation weights are generated • LibCF supports regridding between mosaics of logically rectangular grid tiles (e.g. cubed sphere, single tile logically rectangular) • Currently first order conservative interpolation methods are supported, and some specific bilinear cases

  10. Combining ESMF and LibCF • LibCF was introduced into the ESMF online regridding software. • This was somewhat awkward because LibCF requires Gridspec files as input, but ESMF online regridding holds grid descriptions in memory. • As a result, ESMF must convert its grid descriptions to Gridspec files and then have LibCF read them in. • This works, but more efficient connections could be made with regridding libraries that did not require file input.

  11. Implementation Steps:Getting Interpolation Weights • Write ESMF grids to NetCDF files • Take an existing ESMF grid and get the coordinate information out of it • Write out the coordinate information to a NetCDF file • Done using ESMF I/O functionality • Create mosaic files from the NetCDF grid • Done using LibCF’s make_mosaic function • Get interpolation weights from LibCF • Call LibCF’s regridding function through ESMF calls • Read in LibCF’s interpolation weights into ESMF • Convert interpolation data to a form that ESMF’s sparse matrix multiply can use

  12. Implementation Steps:Weight Application • Apply LibCF interpolation weights to field data using the ESMF sparse matrix multiply call • Future regrid calls to updated field data can bypass the LibCF interpolation weight generation step • This holds as long as the grids involved remain the same

  13. LibCF/ESMF Regridding Flow ESMF Destination Grid Source Grid Weight Matrix Create Mosaic Write Tile Create Weights Read Weights LibCF Regrid fregrid Source Variable Data Destination Variable Data make_mosaic File I/O Legend: NetCDF File Destination Tile Source Tile Source Mosaic Destination Mosaic Remap File API Call ESMF Data

  14. ESMF User Interface for Regridding with LibCF • Actual interface that users employ contains two steps: • ESMF_FieldRegridStore(): Provide source/destination grids and receive interpolation weights • ESMF_FieldRegrid(): Provide interpolation weights and source field data to receive interpolated field data corresponding to the destination grid • This is the same sequence of calls used for pure ESMF regridding

  15. Current Status • Can read interpolation weight information generated by LibCF into ESMF sparse matrix representation and perform a regrid. • Can write ESMF grid structures to Gridspec files • ESMF restriction: • Writing Gridpsec files from ESMF is serial and thus restricts the scaling of the final code • Intersection of LibCF/ESMF capabilities: • Only supports single tile logically rectangular grids • LibCF restriction: • Only supports first order conservative remapping for this geometry

  16. Future Work • Parallel I/O for writing Gridspec files • Switch to non-file based interface if LibCF develops one • Allow for regridding of more complicated grids including the cubed sphere

  17. References • Hill, C., C. DeLuca, V. Balaji, M. Suarez, and A. da Silva (2004). Architecture of the Earth System Modeling Framework. Computing in Science and Engineering, Volume 6, Number 1, pp. 18-28. • Balaji, V., Liang, Z. Gridspec: A Standard for the Description of Grids Used in Earth System Models. http://www.gfdl.noaa.gov/~vb/gridstd/gridstd.html • The CF Library Users Guide. http://www.unidata.ucar.edu/software/libcf/docs/libcf.html • Hartnett, E. and Rew, R., Experience with an enhanced netCDF data model and interface for scientific data access, 88th AMS Annual Meeting, 24th Conference on IIPS, 2008. • Khoei S.A., Gharehbaghi A. R. The superconvergent patch recovery technique and data transfer operators in 3d plasticity problems. Finite Elements in Analysis and Design, 43(8), 2007. • Hung K.C, Gu H., Zong Z. A modified superconvergent patch recovery method and its application to large deformation problems. Finite Elements in Analysis and Design, 40(5-6), 2004. Questions? scholbro@mail.ucar.edu

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