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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 this client and report back any issues. |
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, the all existing valid MARS requests will also work when using MIR. the mars language stays the same, with the exception of some new keywords. All existing valid MARS requests will also work when using MIR.
Will I get different results?
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EMOSLIB only supports sub-area operations on regular Gaussian or lat-lon grids. MIR is capable of cropping sub-areas and frames directly on global reduced Gaussian grids, including the octahedral reduced Gaussian grid.
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This is done automatically provided both the N-S and E-W boundary limits are divisible by the corresponding increments without remainder. This represents a change in respect to EMOSLIB, which would adjust the area to fit. In the previous example, it would go to the more conventional area 90/0/-90/359.
Land-Sea Mask
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.
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" 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 an intermediate (octahedral or full ? - TBC) 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:
| 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. |
| Red | RESOL=AUTO, GRID=1.0/1.0 | Direct transformation from T1279 to 1.0/1.0, with an automatic truncation to T179 or RESOL=179. |
| Blue | RESOL=179, GRID=F90, and then GRID=1.0/1.0 | Transformation from T1279 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. |
Usage of IFS spectral transform library
While EMOSLIB has its own implementation for the transformations from spherical harmonics to grid space, MIR makes use of the spectral transform library, called Trans from the IFS model. That means MIR behaviour is more consistent to what is done in the model, and will immediately benefit from any improvements made in Trans.
Waves
Due to the differences mentioned above, the nearest neighbour method selects different points due to the difference in the computation of the distance (3D versus 2D). Different treatment of neighbouring missing values produces a smoother interpolation close to coasts.
Also, note that all "Spectra-related" parameters have been classified and are interpolated in the same way as the 2D spectra, using a nearest neighbour in MIR instead of EMOSLIB's bilinear method.
Interpolation from limited-area wave data on a regular lat-lon grid, not working with EMOSLIB, is now supported in MIR.
Rotated grids
MIR does not support the 12-point interpolation method, used by EMOSLIB for rotated grids. Therefore, the default interpolation method used is the linear. Rotated spherical harmonics are not supported in MIR or EMOSLIB.