Graphics: NCL – Example

Rainfall in the model is an accumulative field.
So in order to create rainfall tendencies over a specific time, the data from one time needs to be subtracted from the previous time.
   Example, if you have hourly output, you can create hourly tendencies by subtracting each time from the previous, or you can create 3-hourly tendencies by subtracting, say data at hour 06Z from data at hour 03Z.
 
In the case of a moving nest, you can only do this for overlapping grid points.
Care must be taken when calculating tendencies in this case, as a daily tendency will make little sense, since the nest would have moved so far in 24 hours, that the overlapping area will be very small, see the example below.
   In the plot below the box represents the location of the nest at a given time, and the colored area the overlap of the nest location from 24 hours prior. Plotting tendencies for this time, will make little sense.

 

But when looking at 3 (below left) or even 1 (below right) hour time differences, one can see that the domain movement is small enough that the overlapping regions provide lots of valuable information.
Also see movies of the overlapping areas over time for 3 hour and 1 hour time differences.