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Spectral to grid point transformations
Concept of "RESOL=AV" ("Archived Value") when when going to a lower resolution is different. With MIR, RESOL=AV specifies specifies that the transformation is made first to the corresponding octahedral reduced Gaussian grid (i.e., T1279 → O1280 or T639 → O640) followed by grid point interpolation to the user-specified grid.
Default truncation values for "RESOL=AUTO" ("autoresol"Automatic Truncation) have also changed. MIR uses a formula to truncate the spectral series to correspond to the equivalent linear Gaussian grid, replacing the fixed table used in EMOSLIB. Transformations to regular latitude-longitude grids then use an intermediate full (regular) Gaussian grid.
This diagram illustrates an example transformation going from T1279 to a regular lat-lon 1.0/1.0 grid. Depending on the values of RESOL and and GRID, MIR will follow different paths. As a reference, also the original EMOSLIB behaviour is shown for each case:
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