## Meteorology / ARL Data FTP / Reanalysis

Global NOAA-NCEP/NCAR pressure level reanalysis data archives were reprocessed into the HYSPLIT compatible format and are available on ARL's web site for 1948 through the end of the previous year. Data for each additional year are updated annually. The global data are on a latitude-longitude grid (2.5 degree) and are archived as one file (122 Mb) per month. The GUI menu tab accesses the correct directory with the proper file name using anonymous ftp after the desired year and month have been selected.

The NCEP/NCAR Reanalysis Project is a joint project between the National Centers for Environmental Prediction (NCEP, formerly "NMC") and the National Center for Atmospheric Research (NCAR). The goal of this joint effort is to produce new atmospheric analyses using historical data (1948 onwards) and as well to produce analyses of the current atmospheric state (Climate Data Assimilation System, CDAS). Until recently, the meteorological community has had to use analyses that supported the real-time weather forecasting. More information about the reanalysis project and data can be found at the CDC web site.

A subset of this data (global pressure level only) is available from ARL in a format suitable for transport and dispersion calculations using HYSPLIT through the GUI. Data files are named according to the following syntax: RP{YEAR}{MONTH}.gbl, where R indicates "Reanalysis", P indicates that the data are on pressure surfaces, YEAR is a four digit year, and MONTH is a two digit month. The file suffix identifies the projection as the 2.5 degree global latitude-longitude projection (gbl). The projection details are encoded in the file's index record and are processed by HYSPLIT during trajectory or dispersion computations.

A comparable data set is also available from ECMWF's 40 year reanalysis project. The GRIB files must be downloaded independently from the GUI through a web browser. Although cost free, registration with ECMWF is required. The downloaded ECMWF GRIB data files may be converted through the GUI to the ARL format.

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