...
This dataset was generated through the Metview FLEXTRA interface. Appendix A The chapter on data preparation explains how it works and helps prepare your own dataset if it is needed.
...
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
...
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.
...
| Note | ||
|---|---|---|
| ||
Another problem with global GRIB2 input fields is that FLEXTRA interprets the longitude span of the domain either as 0-360 or 180-540 (!!!) degrees depending on the geometry settings in the GRIB headers. The actual range can be figured out from the header of the FLEXTRA output files. In both cases we need to guarantee that the starting point we specify is in the given coordinate range. Otherwise FLEXTRA fails with the following message:
In the first case it is trivial to ensure itwe have the right coordinate values, while in the second case we need to add 360 to the longitude to make FLEXTRA accept the starting point. |
...
There is also a macro equivalent command for icon FLEXTRA Prepare, which is used to prepare input data for FLEXTRA. Please see Appendix A the chapter on data preparation 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
| Warning |
|---|
This automatically generated 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. |
...
It is recommended to use an alternative way and write our own 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.
...
| Code Block |
|---|
#Metview Macro resFile="res_normal_macro.txt" if not(exist(resFile)) then run_normal = flextra_run( ... ) write(resFile,run_normal) else run_normal=read(resFile) end if plot_normal = flextra_visualiser( flextra_data : run_normal ) plot(plot_normal) |
Our code now contains an if statement to check if the FLEXTRA output file exits. If it does not exist we run FLEXTRA to compute the trajectories and save the resulting data into this file using the write() function. Otherwise we read the file from the disk with the read() function into our run_normal variable.
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.
...
Finally we add our objects to the plot() command:
| Code Block |
|---|
plot(flx_plot,title) |
Now, if If you run this macro you should see your plot with the custom title in the Display Window.
Remarks
...
| Tip |
|---|
|
Please find below the list of the metadata keys used by flextra_group_get():
Key | Description | Might get a nil value |
|---|---|---|
cflSpace | Spatial CFL criterion. |
|
cflTime | Temporal CFL criterion. |
|
direction | Trajectory direction. |
|
dx | West-east resolution of the input grid. |
|
dy | North-south resolution of the input grid. |
|
east | Eastern border of the input grid. |
|
integration | Integration scheme. |
|
interpolation | Interpolation type. |
|
maxInterval | The maximum interval between input fields. |
|
name | The name of group (= 'startComment'). |
|
normalInterval | The normal interval between input fields. |
|
north | Northern border of the input grid. |
|
runComment | Label for the FLEXTRA run. |
|
south | Southern border of the input grid. |
|
startComment | The name of the trajectory group (= 'name'). |
|
startDate | Date of starting points. |
|
startEta | Model level of starting points. |
|
startLat | Latitude of starting points. |
|
startLon | Longitude of starting points. |
|
startPres | Pressure of starting points. |
|
startPv | Potential vorticity of starting points. |
|
startTheta | Potential temperature of starting points. |
|
startTime | Time of starting points. |
|
startZ | Height (above sea ) of starting points. |
|
startZAboveGround | Height (above ground) of starting points. |
|
trNum | Number of trajectories in the group. |
|
type | Trajectory type. |
|
west | Western border of the input grid. |
|
...
Now, if you run this macro you will see the data values appearing in the standard output.
Remarks
...
| Tip |
|---|
The second argument of flextra_tr_get() can also be a single key (instead of a list of keys). In this case the function returns either a single string value, a list or a vector depending of the key specified. |
Please find below the list of the metadata keys used by flextra_tr_get():
...
Key | Description | Retrun Return value |
|---|---|---|
date | Date. | list of dates |
eta | Model level. | vector |
lat | Latitude. | vector |
lon | Longitude. | vector |
pres | Pressure. | vector |
pv | Potential vorticity. | vector |
startDate | Date of starting point. | string |
startEta | Model level of starting point. | string |
startLat | Latitude of starting point. | string |
startLon | Longitude of starting point. | string |
startPres | Pressure of starting point. | string |
startPv | Potential vorticity of starting point. | string |
startTheta | Potential temperature of starting point. | string |
startTime | Time of starting point. | string |
startZ | Height (above sea) of starting point | string |
startZAboveGround | Height (above ground) of starting point | string |
stopIndex | Stop index of computations. | string |
theta | Potential temperature. | vector |
z | Height above sea level. | vector |
zAboveGroundLevel | Height above ground level. | vector |
...
Now, if you run this macro you will see the data values appearing in the standard output.
| Anchor | ||||
|---|---|---|---|---|
|
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.
...
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 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.
...
| Warning |
|---|
Please be aware that the preparation process is currently only working for operational forecasts having 91 or 137 model levels and requires parameter etadot from MARS. Because parameter etadot has only been archived in MARS since 4 June 2008, earlier dates cannot be used. |
...
| Code Block |
|---|
244 2012-02-02 16:08 AVAILABLE 547200 2012-02-02 16:07 EN12020100 547200 2012-02-02 16:08 EN12020103 547200 2012-02-02 16:08 EN12020106 |
If we check the AVAIALBLE AVAILABLE file itself we will see the following content (again, you will see different dates in your file):
...
Right-click and execute to start the data preparations again. This time your icon turnes turns green almost immediately indicating that actually no data retrieval and processing happened. The reason for it is that we set parameter Flextra Reuse Input to 'On'. In this case Metview checks the existence of the data to be generated and if the data is already in place no new data is retrieved. The same happens with the AVAILABLE file.
...
However, please note that it should be used with extra care. The reason for it is that flextra_prepare() is executed asynchronously and if we do not reference the variable it returns we can run into problems. The following macro code illustrates this situation:
...
With this code we want to generate the input data for FLEXTRA with flextra_prepare() but we do not use the variable it returns in flextra_run(). Instead we simply use the path where the generated input data should be located. Now, because flextra_prepare() is executed asynchronously the macro starts to execute it and does not wait until it finishes but jumps immediately to flextra_run(). Then flextra_run() fails because the input data is not yet in place so the macro fails as well.
...
Alternatively we can set the Macro execution mode to synchronous by using the waitmode() function. We need to place it before calling flextra prepare() like this:
| Code Block | ||
|---|---|---|
| ||
waitmode(1) res=flextra_prepare( ... ) flextra_run( ... ) |