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Create a new Observation Filter icon and rename it to filter_obs_t2m, setting these parameters:
Data | Drop the obs.bufr icon here |
Output | Geographical Points |
Parameter | 012004 |
Note that 012004 is the code for 'Dry bulb temperature at 2m'. Confirm that the result of this icon's filtering is a set of geopoints with temperature values.
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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 the Result of a Computation for Further Interactive Use
The result of the above macro does not have to live entirely inside the macro - it can be passed back to the user interface or used as input to other icons. Do this:
- in the above macro, comment out the
plot()
command (using the hash,#
, symbol) - add a new line of code at the end:
return speed
This passes the fieldset speed
back to the user interface. Try it by right-clicking on the macro's icon and selecting examine, save or visualise. This icon can also be dropped into an existing Display Window to plot the data there. It could also be used as an input to another icon, for example a Simple Formula icon, for further processing.
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Now create a new GRIB Filter icon with these parameters:
Data | Drop the uv850.grib icon here |
Param | U |
Grid | 2.5/2.5 |
The result will be the same data interpolated onto a 2.5x2.5 degree grid. Visualise the result and apply the supplied gridpoints icon to confirm the new grid. Visualise the two fields side-by-side with coloured contour shading to also confirm that they look very similar in terms of their data values.
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Metview provides two icons, Geopoints to GRIB and GRIB to Geopoints To Grib and Grib To Geopoints for the purpose of converting between GRIB (gridded) and geopoints (scattered) formats.
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Use a Geopoints to GRIB icon to convert the geopoints result of the fc_obs_diff icon to GRIB. We now have gridded data derived from scattered points. This icon contains some parameters to help define the output grid and the interpolation process used in the conversion; it is also possible to supply a template GRIB file which will be used to define the output grid.
Extra Tasks
Computing statistics fields
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Extracting point values
There are many ways to extact extract the value of a field at a given point or set of points. Try this one - call
with the latitude and longitude of a geographical location and print the result to see which data gridpoint is closest to it.nearest_gridpoint_info
( fieldset,number,number )