## METEOROLOGY / Convert to ARL / NARR Archive

This menu item is intended to convert existing NARR GRIB-1 files to the ARL packed format. The data files to process are determined by selecting any file in the GRIB data directory. Subsequent file names will be constructed automatically between the starting and ending day at the hour interval set by the radio-button. Day and hour must be the last four digits of the GRIB file name: {base}{DD}{HH}. Time intervals of 12 hours or more should be avoided in transport and dispersion calculations. Only one month of data or less should be processed into one output file.

The GRIB files for the North American Regional Reanalysis (NARR) can be downloaded from the NOMADS web page. When selecting data to download, all variables and cycles should be obtained. However, it is necessary to select a subgrid because the GRIB decoder (bit maps not supported) will not work with the full domain due to missing data at the corners. A subgrid, such as 25-50N and 125-65W will cover the CONUS and be converted correctly. This particular grid requires only 11 Mb per GRIB file (versus 55 Mb full domain) and once converted to the HYSPLIT format, will require 28 Mb per day.

As noted above, downloaded files should end with the two-digit day and hour identification. Additional characters need to be deleted from the downloaded GRIB file name. The current naming convention at the NOMADS web page will result in downloading the following file name:

narr-a_221_{YYYY}{MM}{DD}_{HH}{mm}_000.grb

where YYYY=year, MM=month, DD=day, HH=hour, mm=minute.

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