A small tool to convert 2-D fields between ESG grid and Rotated grid (for analysis of wave height and 10-m wind gust in rrfs-based 3DRTMA)

[GangZhao-NOAA]

Description

The rrfs-based 3DRTMA needs to analyze the 2-D significant wave height and 10-m wind gust, which are not the prognostic variables of fv3-lam model. Instead of the Extended Schmidt Gnomonic (ESG) grid of fv3-lam model, the firs guess of these 2 variables retrieved from other sources (e.g., WW3) usually are on Rotated LatLon (RLL) grid (for NA domain) or Lambert Conformal Conic (LCC) grid (for CONUS domain). We need to convert the firstguess of these two variables from other grids to ESG grid before the GSI analysis, so that these two data could be analyzed with other FV3-lam variables together in GSI. Then after the analysis, the analysis fields are on ESG grid and need to be transferred to other grids (eg., RLL or LCC) which are recognizable to the Universal Post-Process (UPP).But those 2 variables (wave height and gust) could not be transferred to other other grids by fv3-lam model, therefore we also need to convert the analyses of the two variables back from ESG grid to other grids. This is the motivation to develop a tool to convert ESG grid to Rotated grid and vice versa for analysis of wave height and wind gust in rrfs-based 3DRTMA.

Solution

Developing FORTRAN code, which reads in 2-D field (from grib2 format firstguessfiles) on Rotated LatLon (RLL) grid, then interpolates the data to ESG grid , then append the 2-D field to the netcdf format fv3-lam firstguess file before the GSI analysis; or reads in 2-D fields (from netcdf format GSI analysis file) on ESG grid, then interpolates (and extrapolates for some points) the data to RLL grid (if this is after analysis, then better interpolates the analysis increments), then dump out the data into netcdf format files.
There are some special variable-dependent treatments: for example, the value of wave height and wind gust must be non-negative, the analysis of wave height should be set as undefined value over the land area, etc.

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[GangZhao-NOAA]

@hu5970
Hi Ming, could you please assign this issue to me? I cannot assign myself as the assignee? I am going to submit the pull request for code review and merge very soon.
Thank you!

[GangZhao-NOAA]

The code development was done and test it. It is the branch "feature/esg_conversion_rtma" in my forked repository: https://github.com/GangZhao-NOAA/rrfs_utl/tree/feature/esg_conversion_rtma