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Fig9.3.2: The red lines show the extent of a very approximate 9km x 9km schematic grid square surrounding a grid point (flag).  This is an example of the variability of land surface within an IFS grid box illustrating the difficulty in assigning a representative roughness length for the whole surrounding grid square.  HTESSEL uses up to six "tiles" to describe the different surfaces in the square to assess fluxes of momentum (Fig 9.3.4), and also fluxes of heat and moisture.  These values are used to evaluate the forecasted parameters (temperature, wind etc) at the grid point (flag).  An HRES  An ENS meteogram for a given location is interpolated from adjacent three four grid points (flags) each derived from HTESSEL within its own surrounding grid square.  In the figure these are from adjoining grid squares that are outside of the picture.  An ENS meteogram is derived from the four grid points surrounding the station.  In this example the grid points might not include any wooded low-level grid points at all.  See Section on Selection of gridpoints for Meteograms for details.    

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