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Interpolation of winds at 1000 hPa affected by::

• use by MIR of using an  intermediate full (regular) Gaussian grid at a resolution corresponding to the target lat-lon resolution for the spectral to grid transformation followed by grid-to-grid interpolation
• use by MIR of using a more accurate truncation of the spectral series corresponding to correspond the target grid resolution to avoid ripples from aliasing effects

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• For transformations to high resolution target grids (0.1x0.1 and 0.125x0.125) for which no spectral truncation occurs
  • differences are at most +/-3.5m/s
  • differences are smaller than +/-0.5m/s for more than 99% of grid points
  These differences are due to the use of MIR making the spectral transformation to an intermediate Gaussian grid followed by grid-to-grid interpolation to the regular lat-lon grid whereas EMOSLIB transforms directly to the lat-lon target grid.
• For transformations to lower resolution target grids:
  • the maximum and minimum differences are significantly larger.
  • differences are smaller than 1 m/s for more than 80% of grid points
  • larger differences are due to sub-optimal default truncation of the spectral series used by EMOSLIB:
    • EMOSLIB uses truncation=T799 for a 0.25x0.25 where target grid compared to the theoretical  ideal used by MIR is of truncation=T719
    • EMOSLIB uses truncation=T319 for a 0.5x0.5 where target grid compared to the theoretical  ideal used by MIR is of truncation=T359
    • EMOSLIB uses truncation=T213 for a 1.0x1.0 where target grid compared to the theoretical  ideal used by MIR is of truncation=T179
    Consequently, fields produced by EMOSLIB are more affected by 'aliasing' than those produced by MIR.
• Generally, the The use of the intermediate grid with MIR generally produces smoother fields.

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