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This tutorial explains how to use the FLEXTRA trajectory model within Metview 4.
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Please note that this tutorial requires Metview version 5.0 or later. |
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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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/scratch/graphics/cgr/flextra_data |
This directory contains folder Data. Here you find a set of GRIB files starting with the string "EN". These files are valid for the period of 2012-01-11 00 UTC to 2012-01-15 00 UTC. There is the AVAILABLE file here as well. It is a parameter file telling FLEXTRA the names and dates of the input GRIB files.
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If global GRIB2 input fields generated by Metview are used in FLEXTRA 5 it incorrectly detects the domain and treats it as a limited area. As a consequence trajectories cannot cross the domain boundaries because the computation stops at the border. | ||
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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 we 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. |
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.
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All the required fields, with one exception, can be retrieved from ECMWF's MARS archive. The only exception is the vertical velocity because FLEXTRA needs the following field for its computations:
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\dot \eta \frac{\partial \eta}{\partial p} |
The problem with this product is that only is archived in MARS and the full product needs to be computed during the data preparation process.
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