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HYSPLIT Meteorological Data Conversion Utilities

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Converting Meteorological Data for HYSPLIT

The example programs and HYSPLIT calculations shown in the other sections of this site all use meteorological data fields that have been interpolated to a regular latitude-longitude grid or projected on a conformal map, compressed and formatted in a standard format. This page contains links to source code and PC executable programs that can be used to convert meteorological data in various formats to a HYSPLIT compatible format (ARL packed). Source code is provided for many of the routines so that customized applications can be developed.

ARL Packed Data Format Overview

Briefly, an ARL packed data file consists of a series of fixed length records, one for each meteorological variable. The records are arranged in time series, with surface fields followed by upper air fields. Each record contains a 50 byte ascii header that provides information about the date, time, variable, and packing constants. This is followed by the packed binary data, one byte per grid point. Each byte represents the difference in value between that point and the previous grid point. A group of records at the same time is preceded by an index record that describes all the variables, levels, and grid information for that time period.

The Gridded Binary Data Format (GRIB)

Meteorological data may be obtained from other sources, but it must first be converted to ARL format. Many meteorological centers archive data in GRIdded Binary (GRIB) format. Although conversion software from GRIB to ARL is provided for some of the most common sources, many of these Fortran programs may still require additional customization, depending upon the contents of the data files. Although it may appear simpler to use GRIB data directly for air quality modeling applications, each meteorological center's GRIB file structure is different. The GRIB standard only defines the content of the individual GRIB record and not the organization of the records that are contained in each file. The ARL formatted data are of constant record length, permitting direct access applications using standard IO statements. The ARL data format is also platform independent.

Meteorological Data Sources

The links below provide resources for converting meteorological data to HYSPLIT-compatible format (most are also available in the data2arl directory of PC HYSPLIT). There is no documentation on how to run these programs, however examination of the source code should be sufficient in most situations. With a few exceptions, almost all of the programs only convert one time period of data per execution. To build a multi-time period file it is necessary to append the results of each execution to a single file. The Unix "cat >>" or DOS "type >>" commands may be used for this process.

The file contains various subdirectories with programs to convert meteorological data files in various formats to a format compatible for direct input to HYSPLIT.

Compile the subroutines in the library first and then the routines in the required sub-directories. It may be necessary to edit the Makefiles in each directory.

Compilation of the C-code in is optional and would replace the comparable calls in the Fortran library. The C-FCSUBS IO routines are faster than their Fortran equivalent.

  • Listed below are some of the converters available in these zip files.


    • Converts global GRIB1 files on a regular latitude-longititude grid from either NOAA's GFS model or the ECMWF model. NOAA model output must be on pressure surfaces, ECMWF output may be pressure or their hybrid coordinate. No external library is required.


    • Converts WRF-ARW NetCDF output files. Requires the installation of the NCAR NetCDF libary. For help with running arw2arl see the Readme file


    • Converts global GRIB2 files on a regular latitude-longititude grid from either NOAA's GFS model or the ECMWF model. NOAA model output must be on pressure surfaces, ECMWF output may be pressure or their hybrid coordinate. Requires the installation of the ECMWF GRIB_API library.

    mm5_v3 / rams5 / rams6

    • Converts MM5 Version 3 DOMAIN files; history files from the RAMS model version and version 6. Version 6 requires the installation of version 5. These programs are no longer actively supported.
Modified: June 13, 2022
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