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 resolution | Statistics of differences | Histogram of differences | Global | Europe |
---|---|---|---|---|
0.1x0.1 | Maximum difference = 4200.527100 Percentage of points with absolute difference < 10.00 = 90.423% | -4201.500000 : -3437.590909 - 0 ( 0.000000%) | ||
0.125x0.125 | Maximum difference = 3884.730225 Percentage of points with absolute difference < 10.00 = 90.403% | -3885.500000 : -3179.045455 - 0 ( 0.000000%) | ||
0.25x0.25 | Maximum difference = 2986.975342 Percentage of points with absolute difference < 10.00 = 90.346% | -2987.500000 : -2444.318182 - 1 ( 0.000096%) | ||
0.5x0.5 | Maximum difference = 2871.975342 Percentage of points with absolute difference < 10.00 = 90.088% | -4143.500000 : -3390.136364 - 1 ( 0.000385%) | ||
1.0x1.0 | Maximum difference = 1291.310547 Percentage of points with absolute difference < 10.00 = 90.020% | -1725.500000 : -1411.772727 - 1 ( 0.001535%) |