Interpolation of all wave fields are affected by the changes to

  • the default interpolation method
  • the distance computation and selection of nearest points
  • the handling of missing values

In particular, the different handling of missing values in the interpolation formula leads to differences close to the coasts and ice shelves.  This is demonstrated here using the model bathymetry field and considering only the differences in the missing values in fields produced by MIR and EMOSLIB.

HRES WAM 0.125 degree reduced lat-lon grid

The model bathymetry has been interpolated from the 0.125 degree reduced lat-lon grid to regular lat-lon grids at different target resolutions using EMOSLIB and MIR and the number of missing values in the resulting fields compared (the values themselves are not considered here).

  • As expected, differences are seen around the coasts.
  • Other parameters may also show differences close to the ice shelves which may change from day-to-day.
  • For wave 2d spectra small values (below approximately 10-4) are encoded with missing values.  As a result, Wave 2d spectra  may show additional differences over sea points well away from the coasts and ice shelves.

The plots show the location of the points that differ:

  • the red dots indicate grid points where wave field produced with MIR has a missing value (indicating a land point) while while that produced with EMOSLIB has a value (indicating a sea point)
  • the blue dots indicate points where the wave field produced with EMOSLIB has a missing value (indicating a land point) while that produced with MIR has a value (indicating a sea point)

TargetStatistics of differencesGlobalEurope

Number of points different =  114
     Sea (EMOSLIB) to Land (MIR) = 49
     Land (EMOSLIB) to Sea (MIR) = 65

Percentage of points unchanged = 99.997%


Number of points different =  37
     Sea (EMOSLIB) to Land (MIR) = 14
     Land (EMOSLIB) to Sea (MIR) = 23

Percentage of points unchanged = 99.996%


Number of points different =  17
     Sea (EMOSLIB) to Land (MIR) = 8
     Land (EMOSLIB) to Sea (MIR) = 9

Percentage of points unchanged = 99.993%


Number of points different =  4
     Sea (EMOSLIB) to Land (MIR) = 3
     Land (EMOSLIB) to Sea (MIR) = 1

Percentage of points unchanged = 99.994%

  • No labels