3.3 Convert Meteorological Data

Meteorological data files are available from a variety of sources. However, most will need to be reformatted for use by HYSPLIT. The Meteorology / Convert to ARL menu tab provides several options that will be discussed briefly below. These data can be in Gridded Binary Format (only GRIB-1 is supported through the GUI), Network Common Data Form (NetCDF), or custom binary formats, such as from NCAR's MM5. A conversion program (API2ARL) from GRIB-2 to the HYSPLIT input format can be found in the data2arl directory. Local compilation is required to use these programs. The HYSPLIT data conversion is necessary because each meteorological model may contain different variable names, data organization, horizontal grid projection, or vertical coordinate systems. Keeping the meteorological pre-processing external to HYSPLIT provides more stability to the base code structure. Note that some of the data conversion programs are only available for UNIX systems.

1. The Convert to ARL tab contains the following sub-menus:


• WRF-ARW: The Advanced Weather Research model output files are in NetCDF (UNIX only).


• Global Lat-Lon: Regular latitude-longitude GRIB-1 files from NOAA and ECMWF global models can be processed from this menu (PC and UNIX).


• ECMWF ERA: GRIB-1 files from the ECMWF's global or Interim reanalysis projects can be processed through this menu (PC and UNIX).


• User entered: This menu permits the user to manually enter one observation point but for several time periods to create a spatially homogeneous custom meteorological file (PC and UNIX). This application will be discussed in more detail in an upcoming section.


2. The various data conversion options will not be discussed in any more detail here because most require either the download of large data files or running your own meteorological model. Both of which are beyond the scope of this tutorial. Note that converting meteorological data can be difficult. For example, although the data may be available in a well-documented format such as GRIB, there is no standard as to which variables may be contained within each file, their temporal resolution, and vertical coordinate system. The conversion of data from each meteorological model or data source may require some customization.

HYSPLIT requires meteorological data on an evenly spaced grid (latitude-longitude or conformal projection) at multiple heights and time periods over the duration of the simulation. These data can be obtained from various sources already formatted for use by HYSPLIT or converted by each user to the proper format. As noted earlier, the source code for most of the data conversion programs is available in the \hysplit\data2arl directory.