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If you do not provide a View, then Metview will use a sensible default View. For instance, when you visualise a GRIB icon a Display Window is automatically generated showing , a default Geographical View containing a global map in a Cylindrical projection is used.
The following picture customised Geographical View shows some of these View concepts. This is a customised Geographical View showing:
- more than one globe's worth of area in a Cylindrical projection.
- data overlay control: 5 infra-red bands (Meteosat-7, Meteosat-10, GOES-13, GOES-15, MTSAT-2) and a temperature field.
- coastlines attributes (e.g. line colour, lat/long increments,...).
concepts including plot position and coloured frames.
The Geographical View 
This is the default View for plotting geographic-based data. This View was discussed previously in Customising Your Plot.
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This view is for plots that are not on a map, and will be covered in another session: Graph Plotting in Metview.
The Annotation View 
This will be covered in another session: Layout in Metview.
The Cross Section View 
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Create a new Cross Section View icon, Visualise it and drop the t_fc24.grib icon into the resulting Display Window. A default cross section along the Equator is generated.
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Create a new Average View icon, Visualise it and drop the t_fc24.grib icon into the Display Window. A default meridional average over the global area is generated. Examine Notice the horizontal axis - it only contains E/W co-ordinates, because the data values have been averaged along N/S meridional lines; for each point of longitude, there is one computed value per 2D field. With multiple fields in the vertical direction we can produce this plot.
Experiment with this icon in a similar way to how you did with the Cross Section View icon. You can use a Contouring icon, e.g. the shade icon, to style the contours of the plotting.
The Annotation View
This will be covered in another session: Layout in Metview.
The Hovmøller View 
The Hovmoeller View icon is a computation/plotting specification for Hovmøller diagrams along a specified arbitrary transect line or a rectangular area. The diagram displays a two-dimensional graph with latitude or height as one axis and time as the other.
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The Thermo View icon is a plotting specification for Thermodynamic diagram plots from a suitable GRIB or BUFR data source. In such a diagram, temperature, humidity (represented by the dew point) and wind values are displayed with respect to pressure.
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. Note that only the Tephigram diagram is currently available, although there exist other types of thermodynamic diagrams, such as Skew-T, Emagram and Stuve.
Create a new Thermo View icon
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, Visualise it and drop the tquv_pl.grib icon into the Display Window.
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A default diagram related to a geographical location [0,0] is generated.
Examine the GRIB icon to see the type of input data this 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 help the conversion to pressure levels fields.Note that only the Tephigram diagram is currently available, although there exist other types of thermodynamic diagrams, such as Skew-T, Emagram and Stuve.
To customise the curves displayed in this plot, you can apply (or edit it first) icon vdline. The changes will be applied to both lines. The ability to customise each line individually (temperature and dew point) will be available in a future release of Metview.
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To customise the wind flags displayed in the plot, do the following:create a new instance of this icon and rename it to vdwind.
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Edit it, setting the following parameters:
Wind Field Type | Flags |
Wind Flag Colour | Coral |
| Wind Flag Length | 1.3 |
Wind Flag Thickness | 2 |
Save/OK the changes and drag it into the Display Window.
Macro example
To demonstrate the use of the View concept in a Macro language, letLet's create a Macro program to analyse the vertical structure of temperature changes in time. This exercise reads two forecast steps, computes the differences and visualises the result in a Cross Section View.
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drop the t_fc24.grib icon into the Macro Editor. A variable called
t_fc24_2e_gribis assigned to the value of theread()command, which reads the GRIB data. Rename the variable to simply bet_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 - t_fc24 drop the two contouring icons, neg and pos, which will be used to show the differences.into the editor
- drop the xs_europe icon into the Macro Editoreditor
- underneath the generated code, type the following line:
| Code Block |
|---|
plot(xs_europe,diff,neg,pos) |
The says, "In the xs_europe view, plot the data field diff using the visual definitions neg and pos."
Your complete macro should look like this:
| Code Block |
|---|
t_fc96 = read("/path/to/home/metview/training/day_2/analysis views/t_fc96.grib")
t_fc24 = read("/path/to/home/metview/training/day_2/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. You can also try plotting the difference fields in a default Geographic View by simply omitting omit xs_europe from the plot() command; in this case, Metview chooses the default view for GRIB data, which is a Geographic View. The data will then be plotted on a map.
AlsoFinally, Examine the two input GRIB iconsto analyse their contentssee how the fields differ in terms of date, time and step.
View / Data Modules
Metview uses a netCDF format internally for the results of some computations (this format will be covered in the 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 icon. 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.
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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.