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MIR stands for Meteorological Interpolation and Regridding and is a interpolation and regridding tool and library. This new piece of software is replacing the veteran EMOSLIB when it comes to perform those operations in MARS. Beyond this, MIR’s flexible design facilitates scalability improvements and additional features. These include efficiency gains, a high degree of user configurability, and support for a wider range of grids than in the current package.
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You can try the new MIR-enabled MARS client with:
You are encouraged to try test this new version of the MARS client and report back any issues to advisory@ecmwf.int. |
Questions and Answers
Why are you changing?
The EMOSLIB interpolation package was written in the 1980s and much has changed since then: the model grid resolution has steadily increased, a variety of grid types have been introduced, and many new parameters have been added over the years, often associated with different processing requirements. Both software and hardware technologies, such as programming languages, design paradigms, supporting libraries and hardware architectures, have evolved significantly. Together with new numerical methods and ECMWF's improved understanding of user requirements, all these aspects have prompted ECMWF to design the new, extensible and easy-to-maintain MIR package
Do I need to change my MARS requests?
No, all existing valid MARS requests will also work when using MIR. the mars language stays the same, with the exception of some new keywords. Some new keywords have been introduced for new features such as:
- The usage of an intermediate grid when transforming from Spectral Harmonics to lat-lon grids,
- Custom Land-Sea Mask processing.
TODO: add links to the actual new keywords once they have been agreed.
Will I get different results?
MIR has gone through a thorough validation process and tests to ensure its quality and correctness. However, since the implementations and strategies used in both packages are different, you may see some differences when using MIR instead of EMOSLIB. How significant those differences will be will depend on each specific case.
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MIR will also compute distance in 3D whereas EMOSLIB computes distances on the 2D lat-lon grid. Consequently, different nearest points may be selected for the interpolation methods, and the nearest neighbour method should improve as a result.
Parameter
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classification
In MIR, parameters have been classified into groups, or "classes", which which have an associated default interpolation method. As a result some parameters will now have a significantly different default interpolation method compared to EMOSLIB. Most parameters will use the default linear method in MIR, while some specific classes groups will use a different the nearest neighbour method:
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- index parameters: associated to a table
- spectra parameters: intensity as a function of discrete wavelengths
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- vegetation cover ratio parameters
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- All the rest
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| Unlike EMOSLIB, MIR does not use any special processing for precipitation fields like EMOSLIB. |
Sub-areas
MIR brings a number of improvements in the sub-area and cropping operations.
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By default, MIR does not use land-sea mask processing for any parameters. However, users can specify the land-sea mask to use LSM processing for both input and output grids.
TODO: describe the new MARS keyword once it has been agreed
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Note that as a consequence, MIR does not apply land-sea mask processing when using the nearest neighbour method, which was the case in EMOSLIB. |
Spectral to grid point transformations
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" ("autoresol") 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 uses use an intermediate (octahedral or full ? - TBCfull (regular) Gaussian grid (TBC).
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, also the original EMOSLIB behaviour is described for each case:
| Path | Keywords | MIR Behaviour | EMOSLIB Behaviour |
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| Green | RESOL=AV, 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. |
| Red | RESOL=AUTO, GRID=1.0/1.0 | Transformation from T1279 to the 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. | Direct transformation from T1279 to 1.0/1.0, with an automatic truncation |
| to T213 according to EMOSLIB's truncation table | |||
| Blue | RESOL=179, GRID=F90, and then GRID=1.0/1.0 TODO: use the new keyword once it has been agreed | Transformation from T1279 to the 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. | Same as in MIR, but a separate MARS request is needed for each of the two steps. |
Usage of IFS spectral transform library
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