How can I set the values of a field to zero over a given area? - Metview FAQ

How can I set the values of a field to zero over a given area?

Step-by-step guide

You need to use the mask() macro function. Let us suppose that the field is stored in fieldset g. Then the macro code goes like this:

1. #Define a mask for the area (Southern Hemisphere in this case). It contains 
   #1s for the points within the area and 0s for points outside the area.
   
   mask_sh=mask(g,[0,-180,-90,180])
   
   #We take the "inverse" of this mask and multiply the original field with it.
   #Now, r contains the original values from g outside the mask area, and
   #0s inside the mask area.
   
   r=g*(1-mask_sh)

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