NCEP Global Reanalysis

The NCEP Global Reanalysis (GR) 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. These analyses are very inhomogeneous in time as there have been big improvements in the data assimilation systems. This played havoc with climate monitoring as these improvements were often produced changes in the apparent climate. Even fundamental quantities such as the strength of the Hadley cell has changed over the years as a result of the changes in the data assimilation systems.

The quality and utility of the re-analyses should be superior to earlier NCEP analyses because:

(1) a state-of-the-art data assimilation system is used;
(2) more observations (later data cut-off time) are used;
(3) quality control has been improved;
(4) the model/data assimilation procedure remains essentially unchanged during the entire NCEP/NCAR Reanalysis project (1948-1995) and for the ongoing CDAS (Climate Diagnostics Assimilation System). (Of course there will be some changes as the types and numbers of observations change over the years.)
(5) many more fields are being saved (ex. potential vorticity on isentropic surfaces, diabatic heating);
(6) global coverage (some older analyses were hemispheric); and
(7) better vertical resolution (stratosphere).