NOTE: It is recommended that NCEP/NCAR Reanalysis Users review the known problems associated with the Reanalysis. Please see the Problems section below for links to various web sites detailing these problems.

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. 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 above was taken from NCEP's NCEP/NCAR Reanalysis web page

The National Centers for Environmental Prediction (NCEP) and National Center for Atmospheric Research (NCAR) have cooperated in a project (denoted "reanalysis") to produce a retroactive record of more than 50 years of global analyses of atmospheric fields in support of the needs of the research and climate monitoring communities. This effort involved the recovery of land surface, ship, rawinsonde, pibal, aircraft, satellite, and other data. These data were then quality controlled and assimilated with a data assimilation system kept unchanged over the reanalysis period. This eliminated perceived climate jumps associated with changes in the operational (real time) data assimilation system, although the reanalysis is still affected by changes in the observing systems. During the earliest decade (1948-57), there were fewer upper-air data observations and they were made 3 h later than the current main synoptic times (e.g., 0300 UTC), and primarily in the Northern Hemisphere, so that the reanalysis is less reliable than for the later 40 years. The reanalysis data assimilation system continues to be used with current data in real time (Climate Data Assimilation System or CDAS), so that its products are available from 1948 to the present. The products include, in addition to the gridded reanalysis fields, 8-day forecasts every 5 days, and the binary universal format representation (BUFR) archive of the atmospheric observations. The products can be obtained from NCAR, NCEP, and from the National Oceanic and Atmospheric Administration/ Climate Diagnostics Center (NOAA/CDC).

The above was taken from the 2001 BAMS NCEP/NCAR Reanalysis article

Kalnay, E., Kanamitsu, M., Kistler, R., Collins, W., Deaven, D., Gandin, L., Iredell, M., Saha, S., White, G., Woollen, J., Zhu, Y., Leetmaa, A., Reynolds, B., Chelliah, M., Ebisuzaki, W., Higgins, W., Janowiak, J., Mo, K.C., Ropelewski, C., Wang, J., Jenne, Roy, Joseph, Dennis. 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bulletin of the American Meteorological Society: 77, pp. 437-472.

Kistler, Robert, Kalnay, Eugenia, Collins, William, Saha, Suranjana, White, Glenn, Woollen, John, Chelliah, Muthuvel, Ebisuzaki, Wesley, Kanamitsu, Masao, Kousky, Vernon, van den Dool, Huug, Jenne, Roy, Fiorino, Michael. 2001: The NCEP-NCAR 50-Year Reanalysis: Monthly Means CD-ROM and Documentation. Bulletin of the American Meteorological Society: 82, pp. 247-268.

There has been a number of reported problems associated with the NCEP/NCAR Reanalysis. It is recommended that NCEP/NCAR Reanalysis Users review the known problems. Several institutions have web pages devoted to providing information, although some provide details on both general Reanalysis issues and problems specific to their own Reanalysis Data. A list of these sites is provided here:

• NCEP (General Reanalysis Problems)
• NOAA-CIRES CDC (General Reanalysis Problems, CDC Data Specific Problems)
• NCAR's DSS (General Reanalysis Problems, NCAR Data Specific Problems)

Kevin Trenberth, David Stepaniak, and Julie Caron of NCAR's Climate Analysis Section have recomputed and updated the vertically integrated monthly mean mass, moisture, heat, and energy budget products derived from the NCEP/NCAR Reanalysis, and created a web page displaying their work on the CAS Data Catalog. Prospective users of Mass, Moisture and Energy Budget Products from the NCEP/NCAR Reanalysis should look at the CAS Data Catalog to view details of their work/data.

Updated: 10/29/03
Maintained by asphilli@ucar.edu