VAPOR tutorial

This tutorial explains how to convert ECMWF GRIB data into VAPOR format and how to visualise the resulting data in VAPOR.

Pressure level data

In this exercise we will see how to use pressure level ECMWF GRIB data with VAPOR. We will work with fields from yesterday's forecast on a low resolution grid over Europe.

Getting the GRIB data

First, we retrieve our GRIB data from MARS. We will need two MARS retrieval icons: one for the surface and one for pressure levels.

Now create a MARS Retrieval icon for the surface fields. Rename it 'ret_pl_surf', then apply the following settings:

Create another MARS Retrieval icon for the pressure level fields. Rename it 'ret_pl' and edit it in the following way:

Setting up Vapor Prepare

Having set up the retrievals we can focus on the conversion of the data into the VAPOR format.

Now, create a VAPOR Prepare icon.

Rename it 'vapor_pl' and open up its editor.

First, we need to ensure that Vapor Input Mode is set to 'Icon' then drop the two Mars Retrieval icons into the Vapor Input Data field.

Second, we define the list of GRIB parameters we want to see in VAPOR.

Third, we set the vertical coordinate system:

We set the vertical grid type to 'Layered' and defined geopotential (z) as the parameter holding the elevation of the vertical layers (pressure levels). We also specified the vertical coordinate range (in metres) that VAPOR will display.

Last, we specify the name and location of the results of the conversion:

With these settings a VDF file called 'tut_pl.vdf' will be created in the directory you specified. All the other VAPOR data files will be placed into this directory into a subdirectory called 'tut_pl_data'. By setting Vapor Reuse Vdf to 'On' we told VAPOR Prepare not to run the conversion if a VDF file already exits in the target location.

Now save your VAPOR Prepare icon then right click Execute to run the conversion. The will first turn orange then green when the conversion finishes.

Visualise

Right click Visualise your VAPOR Prepare icon to start up VAPOR. You will see this window popping up:

Now go to the Data → Load a Dataset into Current Session menu and load the vdf file you have just created with your VAPOR Prepare (here you need to find use the path you specified in Vapor Output Path).

Having loaded the vdf file you get something like this:

If you rotate the cube in the display window (middle mouse button) you will see it is flat. We need to scale the vertical axis to get a better view of the whole 3D volume. Go to the Edit → Edit Visualiser Features menu and set the Z Scene Stretch Factor to 200:

Now the full 3D volume is visible:

Next, we load a pre-installed map image to get a better geographical reference for the domain we are looking at. Open the Image tab and load 'BigBlueMarble.tiff' by using the Select Installed Image button. Then tick Instance: 1 at the top of the Edit tab. The scene has now changed like this:

Having set up the view we can now visualise our data.

Explaining further details about VAPOR visualisation goes beyond the scope of this tutorial. For an in depth introduction please study the VAPOR tutorials at:

https://www.vapor.ucar.edu/docs/vapor-tutorials

Model level data

Getting the GRIB data

First, we retrieve our GRIB data from MARS. We will need two MARS Retrieval icons: one for the surface and one for model levels.

Now create a MARS Retrieval icon for the surface fields. Rename it 'ret_surf_ml', then apply the following settings:

Create another MARS Retrieval icon for the model level fields up to level 20. Rename it 'ret_pl' and edit it in the following way:

Setting up Vapor Prepare

Having set up the retrievals we can focus on converting the data into the VAPOR format.

Now, create a VAPOR Prepare icon. Rename it 'vapor_pl' and open up its editor.

First, ensure that Vapor Input Mode is set to Icon then drop your two Mars Retrieval icons into the Vapor Input Data field.

Second, define the list of GRIB parameters you want to see in VAPOR.

Third, set the vertical coordinate system:

We set the vertical grid type to layered and defined geopotential (z) as the parameter holding the elevation of the vertical layers (pressure levels).  Internally, a VAPOR Prepare converts this parameter for metres units and rename it ELEVATION (this is required by VAPOR). We also specified the vertical coordinate range (in metres) VAPOR will display for this data.

Last, we specify  the name and location of the results of the conversion:

With these settings a VDF file called 'tut_pl.vdf' will be created in the directory you specified. All the other VAPOR data files will be placed into this directory into a subdirectory called 'tut_pl_data'. By setting Vapor Reuse Vdf to On we told VAPOR Prepare not to run the conversion if there is a VDF file already exists in the target location.

Now save your VAPOR Prepare icon.

Running Vapor Prepare

Right-click on the VAPOR icon and Execute to run