ECMWF/WCRP level III-A Global Atmospheric (TOGA) Data Sets

The Level III-A archive is subdivided into three classes of data sets:

• Basic Level III
• Supplementary Fields
• Extension

The data sets are based on quantities analysed or computed within the ECMWF data assimilation scheme or from forecasts based on these analyses.

The Basic Data Set contain selected analysed values in a compact form at a resolution of 2.5° x 2.5°. They are particularly suitable for users with limited data processing resources. Derived quantities (fluxes, etc.) are not included, but can in principle be calculated from the data provided in the data sets.

The Supplementary Fields Data Set contains additional surface data, fluxes and net radiation data derived from short-range forecasts used as first-guess data for the analyses. Most of the fields in this data set contain values accumulated over the first 6 (or 12) hours of the forecast. The exceptions, total cloud cover fields, contain instantaneous 6 (or 12) hour forecast values. This is a subset of the operational first-guess surface data.

The Extension Data Set contains additional surface data, fluxes, net radiation data and precipitation derived from 24-hour forecast values. All the fields in this data set contain values accumulated between time step 12 and time step 36 of the forecast.

The archive is currently maintained using the WMO FM 92-IX Ext GRIB (grid in binary) form of data representation, with ECMWF local versions of GRIB Table 2. All fields of data are global within the archive.

A full extraction service is supported, enabling users to obtain sub-areas of data and data at various resolutions on regular Gaussian or latitude/longitude grids, or as spherical harmonics with selected triangular truncation. All extracted data are delivered using the GRIB representation.