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Create a new Simple Formula icon and rename it to fc_an_diff. Edit the icon, ensure that the first Formula type is selected (F+G) and that the operator is minus ( - ). Drop your temperature_forecast.grib icon into the Parameter 1 box, and drop temperature_analysis.grib into the Parameter 2 box. Save the icon and execute it. The icon should turn green, indicating the result has been computed and cached. Further operations on this icon will not re-compute the result unless either of its input icons are modified. If you simply wanted the result to be stored, you could right-click and choose save result to bring up a file save dialogue; but instead choose visualise to plot it. Note that all 6 fields in each data icon are used in the computation - the result is a set of 6 fields.
Two Contouring icons are supplied, which can be used to show the differences. Drop pos_shade and then neg_shade into the Display Window. Notice that the second one replaces the first one - this is not what we want! Select both icons with the mouse and drop them both together into the Display Window to use them both in the plot. Edit the icons to see which parameters were used to create the positive and negative shading effects. There is also a Contouring icon called rainbow_diffs - this uses Metview's ability to draw isolines of different colours rather than using shading. This can be useful if it is important to see another layer underneath the temperature.
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- apply some shading to the data with a Contouring icon, only contouring wind speeds above 20m/s
- note that we use Wind Plotting icons to modify the plotting of vector fields, but this is now a scalar field, so we use the Contouring icon
- overlay the original wind field and change the colour of the arrows to 'charcoal' with a Wind Plotting icon
- shade the land and the sea with a Coastlines icon
Returning a Computation for Further Interactive Use
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