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  1. Global 1km resolution surface elevation data
  2. Reduce to 5 km resolution by smoothing
  3. Compute mean orography at model resolution grid points
  4. Subtract model orography (3) from 5km orography (2) grid points
  5. Compute standard deviation, slope, orientation and anisotropy for every grid box



The spectral representation of orography in the IFS, can:

  • smooth model orography and local effects can be under-identified.
  • lead to "topographic ripples" over adjacent sea/large lakes, which decay with offshore distance, and which are most prominent where there are steep-sided high mountains nearby.