The Reanalysis Project is a joint venture between the National Centre for Environmental Prediction (NCEP) and the National Centre for Atmospheric Research (NCAR). This project aims at producing new atmospheric analyses using historical data collected since 1948 and at analysing the current atmospheric state. 

Historical data collected since 1948 provided valuable long term information about the weather in order to correlate current measurements and to improve the forecasting of the climate evolution, even if techniques have largely changed during the last 60 years. 

The reanalysis project is particularly useful when we want to evaluate the wind resource on a particular site. The NCEP and the NCAR have performed a modern numerical weather analysis and modelling system which allows analysis of global weather observations.

This reanalysis uses a global data assimilation system, along with observations from the land, sea (from ships and marine buoys), aircraft, satellite and other data to produce global fields of various meteorological parameters. The quality of the data is controlled and assimilated by the data assimilation system which has been kept unchanged over the reanalysis period. To increase the reliability of the wind data, the reanalysis also uses delayed observations.

Very recently, a new satellite product has become available that provides measurements of wind with high spatial resolution. The database has been improved with many observations not available in real time for operational use provided by many countries and organisations. The reanalysis system continues to be used with current data in real time, which makes the database as complete as possible. 

Most data collected are saved every 6 hours, so four times a day. The database is periodically updated as new processing and modelling techniques become available. This continuous improvement ensures that every year is treated in a consistent manner. All changes in the model are systematically tested by running two months of assimilations in the summer and in the winter, and 25 forecasts from each assimilation.

NCEP Reanalysis 2 data used in this project provided by the NOAA-CIRES ESRL/PSD Climate Diagnostics branch, Boulder, Colorado, USA, from their Web site at http://www.cdc.noaa.gov/

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