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The new MARS client with the MIR interpolation library is currently in BETA, and it is meant for tests only. Do not use it for any operational purpose. You can try the new MIR-enabled MARS client with:
You are encouraged to test this new version of the MARS client and report back any issues to advisory@ecmwf.int . |
MIR stands for Meteorological Interpolation and Regridding and is a a library of routines for interpolation and regridding tool and libraryof meteorological fields. 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. See the related article in the ECMWF newsletter no.152 for a more complete description of this new library.
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Questions and Answers
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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. |
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These aspects, together with new numerical methods and ECMWF's improved understanding of user requirements, |
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have prompted ECMWF to design the new, extensible and easy-to-maintain MIR package |
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No, all existing valid MARS requests will also work when using MIR. Some new keywords will be introduced for new features such as: |
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MIR has |
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undergone 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. |
Highlights and main differences
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By default, MIR uses a linear method (based on a triangular mesh) which replaces the EMOSLIB bilinear method (based on 4 points).
MIR will also compute computes 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.
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In MIR, parameters have been classified into groups, 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 groups or parameters will use the nearest neighbour method:
- index parameters: associated to a table
- ocean wave spectra abd associated parameters: intensity as a function of discrete wavelengths
- vegetation cover ratio parameters
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Consistency with fields from dissemination
MIR will now move moves the boundaries inwards onto an underlying global grid with a point at latitude=0, longitude=0. This behaviour is a change in respect to EMOSLIB, and it brings it closer to the product generation for dissemination.
Subareas
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of reduced Gaussian grids
EMOSLIB only supports sub-area operations on regular Gaussian or lat-lon grids. MIR is capable of cropping sub-areas and frames directly on from 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 EMOSLIB would adjust the N/W/S/E boundaries to the more conventional area 90/0/-90/359.
Land-
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sea mask processing
By default, MIR does not use land-sea mask processing for any parameters. However, users will be able to specify the land-sea mask to use LSM processing for both input and output grids with a new set of MARS keywords.
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| Path | Keywords | MIR Behaviour | EMOSLIB Behaviour |
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| Red | RESOL=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 | 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 | Transformation from T1279 to the F90 full (regular) Gaussian grid (with an automatic 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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