3.2 FTP Meteorological Data


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Although not needed for this tutorial, meteorological data files already formatted (ARL format) for use by HYSPLIT are available from several different FTP servers. These archives can be accessed directly using any FTP client or through the GUI from the Meteorology / ARL Data FTP tab. This menu provides access to Forecast data, a 24- or 48-h series of Appended forecasts (quasi-archive), a long-term Archive of a variety of different regional and global data files, a special archive of the NCAR/NCEP global Reanalysis, and an option to set the server for the FTP connection.

  1. As an example of how this process works we can download one of the files that will be used later in the tutorial: the global reanalysis data for September 1983. Open the Reanalysis menu and set the year and month. The file name is automatically generated. Get Data File starts the transfer process which opens a progress bar in downloading the 119 Mb file. The downloaded file is much larger than the same named file in the \Tutoria\captex because it is global rather than a regional extract. If you are using a slower wireless network you may not want to download this file or if you are doing this example in a room with 50 other people, do not all click on download at the same time!

  2. In the event of connectivity issues, you can change the FTP server location through the GUI from the Set Server menu selecting from one of three preset options: primary, alternate, or backup. Currently the primary and alternate server access the same hardware but with a different URL. The backup server can only access forecast or appended data files. The primary/alternate and backup servers have different directory structures.

  3. As noted earlier, data files can also be obtained through other FTP clients or even the web browser. This may be necessary for some networks if FTP access is restricted by the system administrator to only a few approved applications. For instance, open the browser to the URL ftp://arlftp.arlhq.noaa.gov/pub/archives/reanalysis to view the files in the directory containing RP198309.gbl.

  4. In contrast, for more current data, the directory structure at ftp://ftpprd.ncep.noaa.gov/pub/data/nccf/com/hysplit/prod is linked with the current date and only forecast data for today and yesterday are available for downloading. For these data, a hardwired connection to this server is also available through the HTTP Data File button which uses the WGET command to download the data files.

One important consideration when downloading meteorological data files is that they are a composite of ASCII and binary fields, where the first 50 bytes of each data record is ASCII then followed by the packed binary data for that field. You should never let the FTP client automatically set the transfer mode, because it may incorrectly determine that the entire file is ASCII. Always insure that the transfer mode is set to binary or image.