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Preparations

First start Metview; at ECMWF, the command to use is metview (see Metview at ECMWF for details of Metview versions). You should see the main Metview desktop popping up.

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and save it in your $HOME/metview directory. You should see it appear on your main Metview desktop, from where you can right-click on it, then choose execute to extract the files. You should now (after a few seconds) see a flexta_tutorial folder which contains the solutions and also some additional icons required by these exercises. You will work in the flextra_tutorial folder so open it up. You should see the following contents:

About FLEXTRA

What is FLEXTRA?

FLEXTRA is an atmospheric trajectory model used by a large user community. It can be driven by meteorological input data from a variety of global and regional models including ECMWF analyses and forecasts.

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About the Metview interface

Metview provides a high level interface to prepare input data for FLEXTRA, run FLEXTRA and visualise the resulting output files. The interface was developed and tested with version 5.0 of FLEXTRA, which is using GRIB API to handle GRIB2 fields.

The input file generation and visualisation do not require the existence of a FLEXTRA executable. However, FLEXTRA itself can be only run if an executable is present. The path to the FLEXTRA executable can be specified for Metview at installation time by setting the --with-flextra switch for configure. However, this path can be overridden at Metview start-up via the MV_FLEXTRA_EXE environment variable.

FLEXTRA is controlled through a set of parameter files which are all generated automatically by Metview in the background. The only exception is file AVAILABLE which can optionally be provided by the users (see Part 3 for details).

The Input Data

The input data needed to run the examples of this tutorial is already prepared for you and located in the directory as follows:

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This dataset was generated through the Metview FLEXTRA interface. Appendix A explains how it works and helps prepare your own dataset if it is needed.

Running FLEXTRA

In this exercise we will see how to compute trajectories with FLEXTRA in NORMAL run mode. In NORMAL mode we can generate a group of trajectories starting from the same point but at different times. Please open folder 'normal' inside folder 'flextra_tutorial' to start the work.

The FLEXTRA Run Icon

To compute trajectories with FLEXTRA we need to use the FLEXTRA Run icon (right-click in the desktop when no icons are selected and use the New icon ... menu).

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With these settings we specified the trajectory type to be three-dimensional (see below for the list of IDs for trajectory types) and set the starting point to volcano Katla (on Iceland) with the height of 1512m.

Remarks  

The format of parameters holding dates is yyyymmdd. Any dates having less than 8 digits are interpreted as relative dates. E.g, -1 = yesterday, 0 = today, 1 = tomorrow etc.

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Running FLEXTRA

Save your FLEXTRA Run icon (Apply) then right-click and execute to start the trajectory computations. Within a minute (it might take longer on your machine) the icon should turn green indicating that the run was successful and the results have been cached.

The FLEXTRA File icon

Our FLEXTRA run generated an ASCII file on output which is now represented by our FLEXTRA Run icon. Right-click and examine the icon to look to see its content. This action will start up a window showing the output generated by FLEXTRA. What you are looking at is a custom ASCII format describing the resulting trajectories and some metadata.

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Visualisation On Maps

In this exercise we will visualise the trajectories that we computed in the previous chapter. We will work in folder 'normal' again.

The FLEXTRA Visualiser Icon

To visualise your FLEXTRA output you need to use a FLEXTRA Visualiser icon.

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At this point we do not need to set any other parameters the default values will work for us. After these modifications your icon editor should look like this.

Visualising the Icon

Save your FLEXTRA Visualiser icon (Apply) then right-click and visualise to plot the trajectories. This will bring up the Metview Display Window using a custom visualisation assigned to FLEXTRA files.

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you will see the meta-data associated with the visualised trajectories.

Customising the Plot

Our plot was generated by using hard-coded symbol plotting settings for trajectory rendering. Now we will change these settings and learn how to customise the graphical properties of individual trajectories.

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• We could have specified a list of symbol heights for parameter Advanced Symbol Table Height List.

Visualisation on XY Plots

In this exercise we will display the temporal evolution of the height of the trajectories we computed in Part 3 . We will generate a graph plot with having the date as the horizontal axis and the height as the vertical axis. We will work in folder 'normal' again.

Creating a FLEXTRA Visualiser Icon

The visualisation is based on the FLEXTRA Visualiser icon just like in the case of the map-based plotting in the previous exercise (Part 4 ).

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After these modifications your icon editor should look like this.

Visualising the Icon

Save your FLEXTRA Visualiser icon (Apply) then right-click and visualise to plot the trajectories.

The Metview Display Window is popping up using a custom visualisation assigned to FLEXTRA files. The title and a legend have been built exactly in the same way as in the map-based visualisation (see Part 4 ).

Customising the Plot

Our plot was generated by using hard-coded symbol plotting settings for trajectory rendering. We can change these settings exactly in the same way as we did for our map-based plot (see Part 4 for details). Now we will not create a new icon but simply reuse the Symbol Plotting icon called 'symbol' we created in Part 4 . Drop this icon into the plot to see the effect of the settings.

Changing the View

We will further customise the plot by changing the axis value ranges and adding axis labels and grid-lines to it. To change these properties we need a Cartesian View icon. This time you do not need to create a new icon since there is one called 'xy_view' already prepared for you. Edit his icon to see how the view is constructed (please note that the axis properties are defined via the embedded Horizontal Axis and Vertical Axis icons). Then simply drag it into the Display Window and see how you plot has been changed.

Backward Trajectories

In this exercise we will see how to compute backward trajectories with FLEXTRA in NORMAL run mode. We will work in folder 'normal' again.

Creating a FLEXTRA Run Icon

Copy your 'run_normal' FLEXTRA Run icon (either right-click + duplicate, or drag with the middle mouse button), and rename the duplicate 'run_normal_back' by clicking on its title. Open its editor and start editing the date and time related parameters (the input data parameters are already set correctly for us so we do not need to change them):

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We selected Reading as the end point and set the height to 1500 metres. We defined the trajectory type to be three-dimensional.

Running FLEXTRA

Save your FLEXTRA Run icon (Apply) then right-click and execute to start the trajectory computations. Within a minute (it might take longer on your machines) the icon should turn green indicating that the run was successful and the results have been cached. Right-click and examine the icon to look at its content. Please note that the first data column contains negative values indicating that we computed backward trajectories.

Visualising the Results

We can visualise the results in exactly the same way as we did in the previous chapter.

Create a new FLEXTRA Visualiser icon. Edit it and drop your 'normal_run_back' FLEXTRA Run icon into the Flextra Data field. Now save your settings (Apply) then right-click and visualise to plot the trajectories. After zooming into the proper area (or dropping the map_Reading icon into the plot) you should see something like this.

CET Run Mode

In this exercise we will see how to compute trajectories with FLEXTRA in CET run mode. In this mode we can generate a set of trajectories starting from the points of a uniform three-dimensional grid. Please open folder 'cet' inside 'flextra_tutorial' to start the work.

Creating a FLEXTRA Run Icon

Create a new FLEXTRA Run icon and rename it 'run_cet' then open its editor.

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With these settings we defined a horizontal grid with only one point (exactly at the position of volcano Katla) and specified four vertical layers from 1500 to 3000 m above seal level.

Running FLEXTRA

Save your FLEXTRA Run icon (Apply) then right-click and execute to start the trajectory computations. Within a minute (it might take longer on your machines) the icon should turn green indicating that the run was successful and the results have been cached. Right-click and examine the icon to look at its content.

Visualising the Results

We can visualise the results in exactly the same way as we did in the previous chapters.

Create a new FLEXTRA Visualiser icon. Edit it and drop your 'run_cet' FLEXTRA Run icon into the Flextra Data field. Now save your settings (Apply) then right-click and visualise to plot the trajectories. After zooming into the proper area (or dropping the map_Katla Map View icon into the plot) you should see something like this.

FLIGHT Run Mode

In this exercise we will see how to compute trajectories with FLEXTRA in FLIGHT run mode. In this mode, we can specify the starting location and starting time for each trajectory individually. It is useful to calculate, for instance, trajectories along the flight track of an aircraft. Please open folder 'flight' inside 'flextra_tutorial' to start the work.

Creating a FLEXTRA Run Icon

Create a new FLEXTRA Run icon and rename it 'run_flight' then open its editor.
First, we need to set the input data parameters (in the same way as we did it in Part 3 ):

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Here we set the trajectory mode to 'FLIGHT' and defined an imaginary flight track called 'track' with 3 points each being valid at a different time.

Running FLEXTRA

Save your FLEXTRA Run icon (Apply) then right-click and execute to start the trajectory computations. Within a minute (it might take longer on your machine) the icon should turn green indicating that the run was successful and the results have been cached. Right-click and examine the icon to look at its content.

Visualising the Results

We can visualise the results in exactly the same way as we did in the previous chapter.

Create a new FLEXTRA Visualiser icon. Edit it and drop your 'run_flight' FLEXTRA Run icon into the Flextra Data field. Now save your settings (Apply) then right-click and visualise to plot the trajectories. After zooming into the proper area (or dropping the map_Eu icon Map View into the plot) you should see something like this.

Using Macro

In this example we will write the macro equivalent of the exercise we solved in Part 3 and Part 4 : we will compute forward trajectories with FLEXTRA in the NORMAL run mode and then visualise them. Please open folder 'normal' inside 'flextra_tutorial' to start the work.

Basics

The implementation of FLEXTRA-related operations in Metview macro follow the same principles as in the interactive mode. In macro we work with the macro command equivalents of the FLEXTRA icons we have seen so far:

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There is also a macro equivalent command for icon FLEXTRA Prepare, which is used to prepare input data for FLEXTRA. Please see Appendix A for details on it.

Automatic macro generation

The quickest way to generate a macro is to simply save a visualisation on screen as a Macro icon. Visualise your 'plot_normal' FLEXTRA Visualiser icon again and click on the macro icon in the tool bar of the Display Window.


Now a new Macro icon called 'MacroFrameworkN' is generated in your folder. Right-click visualise this icon. Now you should see your original plot reproduced.

Please note that this macro is to be used primarily as a framework. Depending on the complexity of the plot macros generated in this way may not work as expected and in such cases you may need to fine-tune them manually. So, we will use an alternative way and write our macro in the macro editor.

Step 1 - Writing a macro

Since we already have all the icons for our example we will not write the macro from scratch but instead we drop the icons into the Macro editor and just re-edit the automatically generated code.

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Now, if you execute this macro (right-click execute or click on the Play button in the Macro editor), Metview will run FLEXTRA to compute the trajectories and you should see a Display Window popping up with the default FLEXTRA visualisation.

Step 2 - Saving and Reading FLEXTRA Data

Duplicate the 'step1' Macro icon (right-click duplicate) and rename the duplicate 'step2'. In this step we will see how to save (write) our FLEXTRA results into a file and read it back into a local variable in order to avoid restarting the FLEXTRA computations every time we change something in the macro.

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Run this macro to make sure that it is working (a FLEXTRA File icon called 'res_normal_macro.txt' should appear in the folder). Then run it again to see that the execution time really became shorter because we bypassed the FLEXTRA trajectory computations.

Step 3 - Customising the Visualisation

Duplicate the 'step2' Macro icon (right-click duplicate) and rename the duplicate 'step3'. In this step we will change our symbol plotting settings and the map area as well.

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Now, if you run this macro you should see your modified plot in the Display Window.

Data Access in Macro

In this example we will see how to read metadata and data from our FLEXTRA outputs. We will get to know the usage of two FLEXTRA-specific macro functions: flextra_group_get() and flextra_tr_get(), respectively. Please open folder 'metadata' in folder 'flextra_tutorial' to start the work.

Step 1 - Using Group Metadata

In this exercise we will read some metadata from our FLEXTRA output and use it to customise our plot's title.

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Step 2 - Accessing Individual Trajectory Data

In this step we will show how to access the metadata and data of individual trajectories.

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Multiple Outputs

In this exercise we will see how to deal with multiple output files generated in a single FLEXTRA run. Please open folder 'multi' in folder 'flextra_tutorial' to start the work.

Multiple Outputs Exercise

So far in all of our examples only one FLEXTRA output file was generated. However, there can be situations when FLEXTRA generates several output files during a single run. It happens when:

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To explain how to handle multiple FLEXTRA outputs we will compute trajectories for multiple starting points with one single FLEXTRA run in NORMAL mode.

Creating a FLEXTRA Run Icon

You will find a 'run_normal' FLEXTRA Run icon in your folder. It is exactly the same icon as you created in Part 3 and it generates trajectories for volcano Katla. Now copy this icon (either right-click + duplicate, or drag with the middle mouse button), and rename the duplicate 'run_multi' by clicking on its title.

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Here we defined two starting points: volcano Katla (as in Part 3 ) and volcano Stromboli. We set the starting heights to the real heights of these volcanoes and again we defined the trajectory types to be three-dimensional.

Running FLEXTRA

Save your FLEXTRA Run icon (Apply) then right-click and execute to start the trajectory computations. Within a minute (it might take longer on your machine) the icon should turn green indicating that the run was successful and the results have been cached.

Examining the Results

In NORMAL run mode FLEXTRA generates a separate output file for each starting point: i.e. in our case two output files were created. However, to have only one access point for all the outputs, Metview concatenates these files into one single file and the Flextra Run icon represents this concatenated file. Now right-click and examine the Flextra Run icon to look at its content.

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A new FLEXTRA File icon will be created in the desktop and if you right-click examine it you will see exactly the same content as above when you examined the FLEXTRA Run icon.

Visualising the Results

Because our 'run_multi' FLEXTRA Run icon stores two groups of trajectories we need to tell the visualiser which one we want to actually plot.

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Save your settings (Apply) then drop the icon into the plot. After zooming into the proper area (or dropping icon 'map_Eu' into the plot) you should see something like this.

Plotting in Macro

In this example we will write the macro equivalent of the visualisation exercise we have just finished.

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plot_Srtromboli=flextra_visualiser(
 	flextra_data: flx,
 	flextra_group_index: 2
 )

Data Access in Macro

In this example we will see how to access metadata and data from a FLEXTRA output file containing multiple trajectory groups.

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  Now, if you run this macro you will see the data values appearing in the standard output.

Input Data Preparation

In this exercise we will see how to generate input data for FLEXTRA runs from ECMWF's MARS archive. Please note that to run the examples you need to have a Metview version being able to connect to MARS. Please open folder 'prepare' in folder 'flextra_tutorial' to start the work.

FLEXTRA Input Data

FLEXTRA expects input data on a regular latitude-longitude grid in GRIB format. The input data must contain four three-dimensional fields: the two horizontal wind components, vertical velocity and temperature. Two additional two-dimensional fields are needed as well: topography and surface pressure.

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In addition to the GRIB files a FLEXTRA run requires several parameter files as well. Most of these files are automatically generated by Metview in the background, so users do not need to create them. The only exception is the file called AVAILABLE describing the input dates, times and GRIB files. This file can be optionally provided by the users (as we saw it in Part 3 ).

The FLEXTRA Prepare Icon

The FLEXTRA Prepare icon is used to generate all the input data needed for a FLEXTRA run including the MARS retrievals, the computations and the generation of the AVAILABLE file as well.

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Running the Icon

Save your FLEXTRA Prepare icon (Apply) then right-click and execute to start the data preparations. After two-three minutes (it might take longer on your system and machine) the icon should turn green indicating that the preparations were successful. The input data preparations involved several Metview tasks in the background:

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DATE TIME FILNAME SPECIFICATIONS
YYYYMMDD HHMMSS
_____________________________________________
20120131 000000 EN12013100 ON DISC
20120131 030000 EN12013103 ON DISC
20120131 060000 EN12013106 ON DISC

Input Data Caching

Edit and save your FLEXTRA Prepare icon (Apply) again. You should see that the title of the icon turned black. For other icons it would mean that the data cached by the icon got deleted. Do not worry, you did not lose your precious data with this action because caching works differently for the FLEXTRA Prepare icon. Even if you delete the icon you will not lose your data and it will remain untouched in the output directory. You need to delete it manually if you want to remove it from the file system. Naturally if you generate a new dataset for the same date, time and steps but with a different grid the original data will be overwritten.

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Running FLEXTRA with the FLEXTRA Prepare Icon

Now we will run FLEXTRA with the data we generated in the previous step. You will find a FLEXTRA Run icon called 'run_normal' in your folder. Open its editor and start editing.

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We can visualise the results in exactly the same way as we did it throughout the tutorial. By using a FLEXTRA Visualiser icon.

Comments on Using FLEXTRA Prepare in Macro

Just like the other FLEXTRA icons the FLEXTRA Prepare icon can also be used in Macro. Its macro command equivalent is flextra_prepare().

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