3.4 Converting NARR GRIB data




Meteorological data files are available from a variety of sources. However, most will need to be reformatted for use by HYSPLIT. In this example we will download Gridded Binary (GRIB1) formatted data files from the North American Regional Reanalysis from the NOMADS FTP server and using the Meteorology / Convert to ARL / NARR Archive menu tab to convert them to the HYSPLIT compatible format. If you are running the Tutorial from the CD you can proceed directly to step 2 because the NARR files can be found in the grib directory.

  1. First open an FTP client of your choice and using anonymous FTP enter the NOMADS server address ftp://nomads.ncdc.noaa.gov . Download data from 1800Z 16 April through 1800Z 17 April of 2007 at 3 hour intervals (9 time periods) that will be used in a later in the example. Go to the NARR data directory /12/narr/200704/200704{16|17} which is configured by year month and day and copy all the files named narr-a_221_200704{16|17}_{HH}00_000.grb to your computer using a binary transfer.

  2. Open the Meteorology / Convert to ARL / NARR Archive menu and set the GRIB input file name to any one of the files you have downloaded. The script will automatically find the other files within the date range specified on the following data entry line, in this case Start Day = 16 and End Day = 17. Set the output file name to NARR16to17.bin and then Process the Data which will result in the a series of messages to the simulation log indicating missing files until 1800 on the 16th and then processing messages through 1800 on the 17th of April. Save the converted file because it can be used in the smoke simulation section.

  3. Additional utility programs are provided in the HYSPLIT exec directory that can be used to examine the contents of a GRIB1 file. These can only be run through the command line. For example, open the command prompt from the GRIB data directory and enter the command ..\hysplit4\exec\inventory and then enter the file name narr-a_221_20070416_1800_000.grb and the summary contents of each GRIB record within the file will be listed to standard output. The listing includes time, variable identification, level, and grid information.

The example shown here converts GRIB formatted NARR archived data into a format that can be used by the model. Although GRIB is a relatively common format within the meteorological community, the file contents, variables, defined grids, and other features may vary depending upon the model and center that produced the GRIB files. Although several GRIB to ARL-HYSPLIT converters are available, some customization may still be required depending upon the GRIB file contents.