Technical Specification on The Implementation of a Trajectory Model


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The trajectory model FLEXTRA has been implemented as a tool that can be used in different analyses of the situation arisen after accidental release of airborne harmful material. The aim of this report is to give the technical specification of the implementation of a trajectory model FLEXTRA that can be used by the administrator and by the user. Some operational elements are also presented, however another technical report will be devoted to include all the relevant aspects in details. The report is organised as follows: first general structure of the implementation is presented, then pre-processing and postprocessing software is fully described. In the appendixes the developed software is included. The application of a trajectory model is presented in a separate report entitled: “Implementation and applications of a trajectory model” by the same authors.

The implementation of the FLEXTRA model – overview

This section gives an overview of the implementation of the FLEXTRA model, all the technical details are put into the next sections. The FLEXTRA model v. 3.3 has been implemented at IES, JRC under Linux-based platform. The diagram below (Fig. 1) shows implementation done at JRC mainly pre- and post-processing. Some small changes have been also made in the source code to increase flexibility of the model.

The pre-processing is related to proper preparation of input data in order to run FLEXTRA simulation. The user can define input data either via interactive script of Unix shell or via simple WWW interface (examples are shown on Figs. 2-4 – depending on chosen options screens can be slightly different – see Figs. 6-9). Once the data are introduced they are converted into proper format of input files via developed Unix scripts (written in Perl language). Another problem is retrieving of needed meteorological data – this can be done in two ways. Firstly it can be achieved via WWW ECMWF site in interactive way. Second possibility is to make it in automatic way. For this purpose additional scripts have been developed namely:

1. To prepare appropriate request to ECMWF system MARS (Meteorological Archival and Retrieval System) and sending it via secure ftp.
2. On ECMWF site background process to proceed with the request and after its completion to send meteorological grib files to JRC site.
3. To combine retrieved grib files from ECMWF into the form expected by the FLEXTRA model (this script is also used after retrieving ECMWF data via WWW).

Once all the input data have been prepared in a proper format FLEXTRA simulation can be initiated. The standard outputs of FLEXTRA are text files. Therefore it has been necessary to develop full post-processing in order to visualize results of simulations on the map and in the form of graphs.
The following scripts have been prepared:
1) To make a picture of each individual trajectory on the map and in the form of graph for the height of trajectory (above see level) in a function of time.
2) To make a picture of all trajectories started at the same time on the map and for height as graph.
3) To make a picture of trajectories within one sub-run (i.e. separately for each perturbed i.e. ensemble run) on the map and for height as graph.
4) Finally all trajectories from all sub-runs (again on map and graph for height).

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