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| Param | T | Note: sets the desired meteorological parameter to Temperature |
| Date | -3 | Note: sets the analysis base time to 3 days ago |
| Grid | 1.50/1.50 | Note: interpolates the result onto a 1.50-degree grid |
To save these settings, click the Apply button at the bottom-left of the icon editor.
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| Type | FC |
| Param | T |
| Date | -5 |
| Step | 48 |
| Grid | 1.50/1.50 |
The analysis data was valid for 3 days ago; this new icon retrieves a 48-hour forecast data generated 5 days ago, so it is also valid for 3 days ago. You don't need to separately execute and visualise the icon - if you visualise it, the data will automatically be retrieved first. The plot title will verify that this data is valid for the same date and time as the analysis data. It also contains the same set of vertical levels.
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Create a new Simple Formula icon by taking a copy from the Macros icon drawer. Rename the copy to fc_an_diff. Edit the icon, ensure that the first tab is selected (F+G) and that the operator is minus ( - ). Drop your temperature_forecast icon into the Parameter 1 box, and drop temperature_analysis into the Parameter 2 box. Save the icon and visualise it. The difference will be computed and the result plotted. Note that all 6 fields in each data icon are used in the computation - the result is a set of 6 fields. The solutions folder contains two Contouring icons which can be used to show the differences: select both pos_shade and neg_shade with the mouse and drop them both into the Display Window (see Figure 6). It is also possible to drop them one at a time, but they do not accumulate - one will replace the other.
| Figure 6 - difference plot with two contour shading icons |
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Click to enlarge |
Automating the whole procedure
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If you examine this icon now, you will see the result: a table of geo-located temperature values. When you visualise the data, you will see that the actual values are plotted as text on the screen; we can do better than this. From the solutions folder, drop the coloured_symbolsmarkers icon into the Display Window. The dark_land_sea_shading icon may also help make the points easier to see.
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| Type | Fc |
| Levtype | Sfc |
| Param | 2t |
| Date | -5 |
| Step | 48 |
| Grid | 1.50/1.50 |
The retrieved data is the 48-hour forecast made 5 days ago for 2-metre temperature.
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