Interpolation of the surface geopotential (and hence, effectively,the orographic height) is affected by the changes to:

  • the land sea-mask processing
  • the default interpolation method
  • the distance computation and selection of nearest points


The geopotential at the surface is also provided in spectral representation as model level (levtype=ml) field, stored on model level 1.  This field is affected differently by changes to the interpolation software.  The parameter described in this page refers to the grid point surface geopotential with levtype=sfc.

HRES - O1280

The surface geopotential  has been interpolated from the O1280 reduced Gaussian grid to regular lat-lon grids at different target resolutions using EMOSLIB and MIR. 

  • For the cases shown here, differences between MIR and EMOSLIB generally lie between+/-4500 m2/s2 (+/- 460 m)
  • In general, more than 99.5% of points differ by less than +/-450 m2/s2 (+/-46 m)
  • The largest differences occur close to the coasts and in areas of steep orography where the gradient of the surface geopotential field changes most rapidly
  • Discounting differences due to land-sea mask processing, the differences between MIR and EMOSLIB generally lie between+/-1800 m2/s2 (+/-185 m) with differences for 99.5% of points being less than +/-160 m2/s2  (+/-16.5m)

The plots show the differences with the contours chosen on a logarithmic scale to enhance the smaller differences.  Differences smaller than 0.1% of the field range are not shown. Grid points where the absolute difference is greater than 25% of the maximum absolute difference are indicated with red (EMOSLIB greater than MIR) and blue (EMOSLIB less than MIR) filled circles.


Target resolutionStatistics of differencesHistogram of differencesGlobalEurope
0.1x0.1

Maximum difference = 4200.527100
Minimum difference = -2743.472900
Mean absolute difference = 6.570708
Median absolute difference = 0.527100
Standard deviation = 34.616588
RMS of differences = 34.617696

Percentage of points with absolute difference

        < 10.00 = 90.423%
        < 100.00 = 98.791%
        < 500.00 = 99.920%
        < 1000.00 = 99.987%



-4201.500000 : -3437.590909 -          0 (  0.000000%)
-3437.590909 : -2673.681818 -          2 (  0.000031%)
-2673.681818 : -1909.772727 -         20 (  0.000308%)
-1909.772727 : -1145.863636 -        225 (  0.003470%)
-1145.863636 : -381.954545 -       3618 (  0.055802%)
-381.954545 : 381.954545 -    6474512 ( 99.859831%)
  381.954545 : 1145.863636 -       4889 (  0.075406%)
 1145.863636 : 1909.772727 -        277 (  0.004272%)
 1909.772727 : 2673.681818 -         38 (  0.000586%)
  2673.681818 : 3437.590909 -         15 (  0.000231%)
 3437.590909 : 4201.500000 -          4 (  0.000062%)

0.125x0.125

Maximum difference = 3884.730225
Minimum difference = -2500.269775
Mean absolute difference = 6.497116
Median absolute difference = 0.730225
Standard deviation = 34.833189
RMS of differences = 34.834725

Percentage of points with absolute difference

        < 10.00 = 90.403%
        < 100.00 = 98.775%
        < 500.00 = 99.918%
        < 1000.00 = 99.986%

-3885.500000 : -3179.045455 -          0 (  0.000000%)
-3179.045455 : -2472.590909 -          1 (  0.000024%)
-2472.590909 : -1766.136364 -         16 (  0.000386%)
-1766.136364 : -1059.681818 -        178 (  0.004289%)
-1059.681818 : -353.227273 -       2709 (  0.065276%)
-353.227273 : 353.227273 -    4143208 ( 99.834413%)
  353.227273 : 1059.681818 -       3697 (  0.089083%)
 1059.681818 : 1766.136364 -        219 (  0.005277%)
 1766.136364 : 2472.590909 -         33 (  0.000795%)
  2472.590909 : 3179.045455 -         15 (  0.000361%)
  3179.045455 : 3885.500000 -          4 (  0.000096%)

0.25x0.25

Maximum difference = 2986.975342
Minimum difference = -2501.024658
Mean absolute difference = 6.421756
Median absolute difference = 0.024658
Standard deviation = 36.891598
RMS of differences = 36.893367

Percentage of points with absolute difference

        < 10.00 = 90.346%
        < 100.00 = 98.733%
        < 500.00 = 99.904%
        < 1000.00 = 99.984%

-2987.500000 : -2444.318182 -          1 (  0.000096%)
-2444.318182 : -1901.136364 -          4 (  0.000385%)
-1901.136364 : -1357.954545 -         23 (  0.002215%)
-1357.954545 : -814.772727 -         96 (  0.009246%)
  -814.772727 : -271.590909 -       1174 (  0.113076%)
 -271.590909 : 271.590909 -    1035253 ( 99.712302%)
   271.590909 : 814.772727 -       1501 (  0.144572%)
   814.772727 : 1357.954545 -        150 (  0.014448%)
 1357.954545 : 1901.136364 -         23 (  0.002215%)
 1901.136364 : 2444.318182 -          9 (  0.000867%)
 2444.318182 : 2987.500000 -          6 (  0.000578%)

0.5x0.5

Maximum difference = 2871.975342
Minimum difference = -4142.024658
Mean absolute difference = 7.259612
Median absolute difference = 0.024658
Standard deviation = 43.622669
RMS of differences = 43.624398

Percentage of points with absolute difference

        < 10.00 = 90.088%
        < 100.00 = 98.533%
        < 500.00 = 99.857%
        < 1000.00 = 99.975%

-4143.500000 : -3390.136364 -          1 (  0.000385%)
-3390.136364 : -2636.772727 -          0 (  0.000000%)
-2636.772727 : -1883.409091 -          3 (  0.001154%)
-1883.409091 : -1130.045455 -         20 (  0.007695%)
-1130.045455 : -376.681818 -        251 (  0.096568%)
  -376.681818 : 376.681818 -     259309 ( 99.764928%)
   376.681818 : 1130.045455 -        311 (  0.119652%)
 1130.045455 : 1883.409091 -         20 (  0.007695%)
 1883.409091 : 2636.772727 -          4 (  0.001539%)
 2636.772727 : 3390.136364 -          1 (  0.000385%)
 3390.136364 : 4143.500000 -          0 (  0.000000%)

1.0x1.0

Maximum difference = 1291.310547
Minimum difference = -1724.689453
Mean absolute difference = 7.614173
Median absolute difference = 0.689453
Standard deviation = 41.118318
RMS of differences = 41.125978

Percentage of points with absolute difference

        < 10.00 = 90.020%
        < 100.00 = 98.465%
        < 500.00 = 99.848%
        < 1000.00 = 99.988%

-1725.500000 : -1411.772727 -          1 (  0.001535%)
-1411.772727 : -1098.045455 -          1 (  0.001535%)
-1098.045455 : -784.318182 -         10 (  0.015347%)
 -784.318182 : -470.590909 -         28 (  0.042971%)
 -470.590909 : -156.863636 -        221 (  0.339165%)
 -156.863636 : 156.863636 -      64598 ( 99.137508%)
   156.863636 : 470.590909 -        230 (  0.352977%)
   470.590909 : 784.318182 -         50 (  0.076734%)
   784.318182 : 1098.045455 -         16 (  0.024555%)
 1098.045455 : 1411.772727 -          5 (  0.007673%)
 1411.772727 : 1725.500000 -          0 (  0.000000%)