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Value | RESOL equivalent | Description | ||
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NONE | - | Disables the use of an intermediate grid
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AUTO | - | An intermediate FULL Gaussian grid is used, derived from the output GRID, by looking at the equivalent resolution. This is the default behaviour | ||
Onumber | Onumber | Use the specified Octahedral Gaussian grid as an intermediate grid | ||
Fnumber | Fnumber | Use the specified Full (regular) Gaussian grid as an intermediate grid | ||
Nnumber | Nnumber | Use the specified Reduced Gaussian grid as an intermediate grid | ||
OFF | OFF | reserved MARS value that resets the value inherited, effectively removing the keyword from the request. In this case results in AUTO being applied. |
Different treatment for RESOL=AV
The concept of "RESOL=AV" ("Archived Value") when going to a lower resolution is different. With MIR, RESOL=AV 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" (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.
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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 GRID, MIR will follow different paths. As a reference, the original EMOSLIB behaviour is also shown for each case:
MIR Behaviour | EMOSLIB Behaviour | ||||||||||||||||
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Path | Keywords | New keywords | MIR Behaviour | EMOSLIB Behaviour |
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Red | RESOL=AUTO, GRID=1.0/1.0 | TRUNCATION=AUTO, INTGRID=AUTO, GRID=1.0/1.0 | Default Behaviour. Transformation from T1279 to an intermediate F90 full (regular) Gaussian grid (with an automatic truncation to T179) followed by a grid-to-grid interpolation from the F90 grid to 1.0/1.0. | Default Behaviour. Direct transformation from T1279 to 1.0/1.0, with an automatic truncation to T213 according to EMOSLIB's truncation table |
Green | RESOL=AV, GRID=1.0/1.0 | TRUNCATION=NONE, INTGRID=AUTOO1280, GRID=1.0/1.0 | Transformation from T1279 to the corresponding intermediate reduced octahedral Gaussian O1280, before going to 1.0/1.0. | Direct transformation from T1279 to 1.0/1.0, with no truncation. |
Blue | RESOL=179, GRID=F90, and then GRID=1.0/1.0 | TRUNCATION=179, INTGRID=F90, GRID=1.0/1.0 | Transformation from T1279 to the F90 full (regular) Gaussian grid (with a user-specified truncation to T179) followed by a grid-to-grid interpolation from the F90 grid to 1.0/1.0. | Same as in MIR, but a separate MARS request is needed for each of the two steps. |
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