Abstract
Abstract. Flex_extract is an open-source software package to efficiently retrieve and prepare meteorological data from the European Centre for Medium-Range Weather Forecasts (ECMWF) as input for the widely used Lagrangian particle dispersion model FLEXPART and the related trajectory model FLEXTRA. ECMWF provides a variety of data sets which differ in a number of parameters (available fields, spatial and temporal resolution, forecast start times, level types etc.). Therefore, the selection of the right data for a specific application and the settings needed to obtain them are not trivial. Consequently, the data sets which can be retrieved through flex_extract by both member-state users and public users as well as their properties are explained. Flex_extract 7.1.2 is a substantially revised version with completely restructured code, mainly written in Python 3, which is introduced with all its input and output files and an explanation of the four application modes. Software dependencies and the methods for calculating the native vertical velocity η˙, the handling of flux data and the preparation of the final FLEXPART input files are documented. Considerations for applications give guidance with respect to the selection of data sets, caveats related to the land–sea mask and orography, etc. Formal software quality-assurance methods have been applied to flex_extract. A set of unit and regression tests as well as code metric data are also supplied. A short description of the installation and usage of flex_extract is provided in the Appendix. The paper points also to an online documentation which will be kept up to date with respect to future versions.
Highlights
The widely used offline Lagrangian particle dispersion model (LPDM) FLEXPART (Stohl et al, 1998, 2005; Pisso et al, 2019) and its companion, the trajectory model FLEXTRA (Stohl et al, 1995; Stohl and Seibert, 1998), require meteorological data in GRIB format as input
The most accurate algorithm for the reconstruction of the native vertical velocity requires the extraction of the horizontal divergence fields and the logarithm of the surface pressure in spectral representation, their transformation to the reduced Gaussian grid, on which the continuity equation is solved, a transformation back to the spectral space, and the evaluation on the latitude– longitude grid desired by users
The parameters Gaussian, levtype and repres are internal parameters not defined as any available input parameter
Summary
The widely used offline Lagrangian particle dispersion model (LPDM) FLEXPART (Stohl et al, 1998, 2005; Pisso et al, 2019) and its companion, the trajectory model FLEXTRA (Stohl et al, 1995; Stohl and Seibert, 1998), require meteorological data in GRIB format as input. After the retrieval of the meteorological fields, flex_extract calculates, if necessary, the vertical velocity in the native coordinate system of ECMWF’s Integrated Forecast System (IFS), the so-called hybrid coordinate (Simmons and Burridge, 1981); it calculates approximate instantaneous fluxes from the accumulated flux data provided by the IFS (precipitation and surface fluxes of momentum and energy) It takes care of packaging and naming the fields as expected by FLEXPART and FLEXTRA. ECMWF opened the access to selected reanalysis data sets for non-member-state users, so-called public users from anywhere in the world, while previously only users with a member-state account could access the data Along with this change, two new web interfaces (ECMWF’s Web API and the Copernicus Data Service, CDS API) were introduced, which allow one to download data without direct access to ECMWF servers. This paper contains the first documentation of flex_extract published in the open literature
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