Page History

The atmospheric model uses a Reduced a Reduced Gaussian Octahedral grid.  This is triangular in nature and . NWP model values are interpolated both onto and from the grid by MIR (Meteorological Interpolation and Regridding) using .  For output purposes, MIR uses a triangular interpolation technique which:

...

.  This uses model grid point values (black points) to interpolate a value for an off-grid location (red point

...

).

Fig3.3-1: The Reduced Gaussian grid is triangular in nature.  The interpolation uses the three corner points (black points) closest to the selected location (red point) and .  It then takes a weighted average based upon the proximity of the point to the to vertices to arrive at the interpolated value.  

In deriving a A value for point P the is derived using a weighting factor apportioned to for each point A,B,C is equal to the area of the diametrically opposite triangle. Therefore the . The weighting for:

• Point A is equal to the area of triangle PBC (pink) divided by area of triangle ABC. (Weighting  = W_A).
• Point B is equal to the area of triangle PCA (cyan) divided by area of triangle ABC. (Weighting  = W_B).
• Point C is equal to the area of triangle PAB (green) divided by area of triangle ABC. (Weighting  = W_C).
• The value at point P is then the sum of these three contributions: i.e. P = (A x W_A) + (B x W_B) + (C  x W_C)

...