## Meteorology / Convert to ARL / ECMWF

This menu tab is intended to convert existing ECMWF GRIB files to the ARL packed HYSPLIT compatible format. 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 are assumed to be the last four digits of the file name: {base}{DD}{HH}. Input files could consist of multiple time period forecasts or single-time period archives. 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. HYSPLIT cannot properly position to the correct starting data record if there is a month transition included within a data file.

The ECMWF input data may be on pressure surfaces or its native hybrid coordinate system. The "number of levels", counted from the surface upwards, can be used to restrict the size of the output file. This may be particularly useful when the input file consists of 60 or more hybrid levels.

Four different grid conversions are available through the menu. The "Extract" option interpolates the data to a conformal map projection of 100x100 grid points at 100 km resolution at the center of the latitude and longitude selection of the slider bar. The Northern- or Southern Hemisphere options create a 95-km resolution polar stereo-graphic grid centered about the pole. The "Input" option results in no interpolation and the program just converts the original latitude-longitude data (global or regional) to the ARL packed format.

The conversions from this menu are intended for data sets created by the operational ECMWF forecast model. These may be forecast or analysis data. Conversion of ECMWF reanalysis data is done through a different menu.

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