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Note that to generate the initial file for a specific grid (uniform resolution or RRM), the grid description file is required (a SCRIP or a .g file). For high-resolution grids, a .g grid file is preferred in order to use TempestRemap to generate high-order map file. See more in step 3.
NOTE: The procedure to generate new initial conditions has been built into into the HICCUP tool (see https://github.com/E3SM-Project/HICCUP), which is a set of flexible and robust python routines to automate and streamline the task of generating a new atmospheric initial condition for E3SM. It can use ERA5 reanlaysis data or regrid (either horizontal, vertical or both) an existing atmospheric initial condition file. HICCUP has its own surface adjustment routine that follows the original adjustment routine published by ECMWF, which was also reproduced in similar tools by Jerry Olson and Wuyin Lin. HICCUP was built with code readability and documentation as a top priority and includes some unit tests for adjustment routines. HICCUP has also successfully been used to generate initial conditions for ne1024 grids using large memory analysis nodes available at HPC centers. Development of HICCUP is ongoing and new features are planned, so any feedback or feature requests are welcome.
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The analysis data are typically provided at regular lat/lon grids. The following fields are mandatory: physical fields of PS, PHSI, T, Q, U, V, and vertical coordinate related variables, namely, P0, hyam, hybm, hyai, hybi for hybrid simga-pressure coordinate and lev and ilev for constant pressure levels. The IFS data provided by the DYAMOND initial is at full 640 gaussian grids, ifs_oper_T1279_2016080100.nc. It contains the required fields but need to be either renamed (t,q,u,v,z_2_ or converted (e.g., lhsp). It has the hybrid coordinate coefficient variables but using different vertical coordinate dimension names than the ones used to define the physical fields. NCO vertical interpolation function may have been updated to recognize such hybrid coefficient variables. The workflow as used here opt to re-define these variables using consistent vertical dimension names. The above can be done using /project/projectdirs/m2136/analysis-IC/ifs_modify.sh. The modified file is named as ifs_oper_T1279_2016080100_mod.nc. Not all variables in the file are needed for IC. A subset of it, ifs_oper_T1279_2016080100_mod_subset.nc, is used for the remaining steps. |
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