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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.

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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 the pressure levels.

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

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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.

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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.

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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, VAPOR Prepare converts geopotential to metres and rename it ELEVATION (this is required by VAPOR). We also specified the vertical coordinate range (in metres) that VAPOR will display.

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Now save your VAPOR Prepare icon then right click Execute to run the conversion.

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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:

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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).

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Having loaded the vdf file you get something like this:

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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:

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Now the full 3D volume is visible:

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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:

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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

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Getting the GRIB data

First, we need to retrieve our GRIB data from MARS. We will need to create two MARS retrieval Retrieval icons: one for the surface and one for the pressure 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 pressure model level fields up to 100 hPalevel 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.

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Now save your VAPOR Prepare icon.

Running Vapor Prepare

 Right-click on the VAPOR icon and Execute to run