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Now create a new Cross Section View icon. Visualise it and drop the t_anfc24.grib icon into the Display Window. A default cross section along the Equator is generated. This is an alternative way to view your data - instead of a geographical plot for instance.

Inspect the GRIB icon (right-click on it and choose examine) to see the type of input data this view View requires,

Edit the Cross Section View icon and change the transect line (coordinates along which the cross-section is calculated).- click on the Geography Tool button to bring up an editor (or type the coordinate by hand). Save your changes in the Cross Section View icon and use it to re-visualise the data with this new cross section.

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Note that you can still drag any valid Contouring icons you may have into the Display Window when visualising a cross section. For instance, apply the given shade icon. You may want to customise it and try different configurations.

Notice that a Cross Section View icon editor contains a place for an embedded Thermo Grid icon, which configures the background attributes of the thermodynamic diagram.

The Vertical Profile View    

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Create a new Vertical Profile View icon. Visualise it and drop the t_anfc24.grib icon into the Display Window. This view shows a vertical profile at a point (or averaged over an area). Experiment with this icon in a similar way to how you did with the Cross Section View icon.

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Create a new Average View icon. Visualise it and drop the t_anfc24.grib icon into the Display Window. A default meridional average over the globe cross-section is generated. Experiment with this icon in a similar way to how you did with the Cross Section View icon.

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Experiment with this icon by changing other parameters, for instance, the font style and size. Also, multiple Text Plotting icons can be placed in this View. Duplicate the note1 icon, rename it, customise it (remember to define an appropriate text box) and drag it into the Display Window.

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Examine the GRIB icon to see the sort of input data this view View requires,

Three types of Hovmøller diagrams can be produced:

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Create a new Thermo View icon. Visualise it and drop the tquv_pl.grib icon into the Display Window. A default diagram related to a geographical location [0,0] long is generated.

Inspect the GRIB icon (right-click on it and choose examine) to see the type of input data this view View requires. Fields Temperature  and Specific Humidity are mandatory and they will be used to compute the Dew Point parameter. Fieldsets U and V wind components are optional, but if given they will be used to compute the wind vectors. If the data is given in model levels then a Logarithm of Surface Pressure field must be provided too in order to convert them help the conversion to pressure levels fields.

Note that only the Tephigram diagram is currently available, although there are other types of thermodynamic diagrams, such as Skew-T, Emagram and Stuve.

Graph Plotting icon????

Macro example

To demonstrate the use of the View concept in a Macro language, let's create a program to analyse the vertical structure of temperature changes in time. This exercise reads two forecast steps, computes the differences and visualise the result in a cross section view.

Create a new Macro icon and rename it to xsdiff. Edit it and do the following:

• drop the t_fc24.grib icon into the Macro Editor. A variable called t_fc24_2e_grib is assigned to the value of the read() command, which reads the GRIB data. Rename the variable to simply be t_fc24.

• drop the t_fc96.grib icon into the Macro Editor. Rename the variable to t_fc96.

• compute the differences, e.g. diff = t_fc96.grib - t_fc24.grib

• drop the two contouring icons, neg and pos, which will be used to show the differences.

• drop the xs_europe icon into the Macro Editor
• underneath the generated code, type the following line:

plot(xs_europe,diff,neg,pos)

Your complete macro should look like this:

t_fc96 = read("/home/graphics/cgk/metview//Analysis Views/t_fc96.grib")

t_fc24 = read("/home/graphics/cgk/metview//Analysis Views/t_fc24.grib")

diff = t_fc96 - t_fc24

pos = mcont(
    legend                         : "on",
    contour_level_selection_type   : "level_list",
    contour_max_level              : 10,
    contour_min_level              : 0.1,
    contour_level_list             : [0.5,1,2,4,10],
    contour_shade                  : "on",
    contour_shade_method           : "area_fill",
    contour_shade_max_level_colour : "red",
    contour_shade_min_level_colour : "orange_yellow",
    contour_shade_colour_direction : "clockwise"
    )

neg = mcont(
    legend                         : "on",
    contour_level_selection_type   : "level_list",
    contour_max_level              : -0.5,
    contour_min_level              : -10,
    contour_shade_max_level        : -0.1,
    contour_shade_min_level        : -10,
    contour_level_list             : [-10,-4,-2,-1,-0.5],
    contour_shade                  : "on",
    contour_shade_method           : "area_fill",
    contour_shade_max_level_colour : "greenish_yellow",
    contour_shade_min_level_colour : "blue",
    contour_shade_colour_direction : "clockwise"
    )

xs_europe = mxsectview(
    line : [55,-6,43,16]
    )

plot(xs_europe,diff,neg,pos)

Now run the macro to generate the plot.

Also, inspect the two input GRIB icons (right-click on it and choose examine) to analyse their contents,

Exporting Modules Data

Metview uses a netCDF format internally for the results of some computations (this format will be covered in another session: Data Part 2). In particular, most of the previous Views (i.e. Cross Section, Vertical Profile, Average, Hovmøller and Thermo) do this, but their result data is not available to the user. Therefore, each of these Views has a corresponding Data Module view. If the intention is to simply plot the result, then the View icons are more useful. But to store the result data, the Data Module icon is required.

Create both a Vertical Profile View and a Vertical Profile Data icon and edit both to see the differences. All the parameters related to the visualisation of the result are only in the View icon, and the Data parameter exists only in the Data Module icon.

Dealing only with the Vertical Profile Data icon now, drop the supplied input GRIB icon t_fc24.grib into the Data parameter box. Set the Point to whatever you like and save the icon. Now if you right-click and Examine the icon, you will see the resulting netCDF file in the NetCDF Examiner. You can also select Save Result to save the result into a file for storage.

All of this can also be put into a macro, where the resulting netCDF variable can be further manipulated before being written to a file (or visualised).

Write a short macro, named save_vp, which computes a vertical profile from the data (use the Vertical Profile Data icon that you already set up) and writes the result to a file. To write a netcdf variable to a file, the syntax is the same as for any other data type:

write('output_file', data)

Your macro should be 3 lines long (well, 3 commands anyway) - one to read the input GRIB file, one to compute the profile and one to write the result to disk.

Data Module

Macro

Annotation View

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