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The standard deviation, slope, orientation and anisotropy of the surface in each grid box can be important for assessment of sub-grid scale local wind effects, solar heating etc.  These are not yet included directly in the atmospheric models.  However, in mountainous areas the upscaled orography is supplemented by fields describing some characteristics of the sub-grid orography (sub-grid scale slope, orientation and anisotropy of the orography - GRIB fields are available for use by forecasters locally).  This allows better parameterisation of the effects of gravity waves and better representation of flow-dependent blocking of the airflow (e.g. cold air drainage trapped in valleys can effectively raise the local orography).  

Compare HRES model orography model orography used by HRES and ENS (resolution 9km),  ENS model orography (up to Day 15, resolution 18km), and  extended-range ENS model orography (used beyond Day15, resolution 36km).  

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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

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