NCEP/NCAR CDAS/Reanalysis Project

TOVS-land rerun
Phase II: Regional Reanalysis
Plots and Data
CDAS on-line data

What is it all about ?
Things are not perfect ... Problem Report
How to get the data

TOVS problem: rerun from 1/97 to present

The TOVS-land problem has be rerun. The data sets are in the process of being updated to revised analyses (March 1, 1997-Sept 18, 2001).
Rotating CDAS archive has been updated.
CDAS monthly archives has been updated.

detailed summary of observational data used by Reanalysis.
background error used by the assimilation system (SSI).

1/3/2000: Y2K problem: some observational data were being incorrectly rejected. This problem only affected the 12/31/1999 analyses were fixed 1/3/2000 (6pm).

News: Found a "truncation" error with the snow analyses. Fixed Dec 1. More details to follow.

Rotating Archives

CDAS is now updated daily and the daily updates are being stored in the "CDAS rotating archives." These archives include more data than in our on-line historical archives such as four times daily analyses and more daily-averaged fields. The historical archives will continue to be updated once a month.

Annual Reanalysis CD-ROMs

1953-1999 Reanalysis CD-ROMs are now available. Contact NCAR for more information.

The Reanalysis Synoptic CD-ROM with global 00Z analyses from 1979-1996 is available. Fields on this CD-ROM include HGT (1000 mb, 500 mb), WINDS (850 mb, 200mb) and OMEGA (500 mb). This CD-ROM, like the annuals, is GrADS compatible and includes an MS-DOS menu system and is available from NCAR .

In the pipeline:
**SOON** ECMWF (ERA) vs NCEP Reanalysis (NCEP access only)
A twice daily, Northern Hemisphere Synoptic CD-ROM
More annual CD-ROMs
BAMS article with CD-ROM with 50 years of monthly means (submitted)

What is it all about ?

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 quality and utility of the re-analyses should be superior to NCEP's original analyses because

  • a state-of-the-art data assimilation is used
  • more observations are used
  • quality control has been improved
  • the model/data assimilation procedure will remain essentially unchanged during the project
  • many more fields are being saved (ex. potential vorticity on isentropic surfaces, diabatic heating)
  • global (some older analyses were hemispheric)
  • better vertical resolution (stratosphere)

For more information ...
*1996 BAMS Paper (Bulletin of the American Meteorological Society)
* 2001 BAMS Paper (Bulletin of the American Meteorological Society) (ftp)
* Misc. abstracts
*Types of Reanalysis Data
* Proc. of the First WCRP Intl. Conf. on Reanalysis (Silver Spring MD, 27-31 Oct 1997)
            WCRP-104, WMO/TD-No. 876
* Reanalysis prior to 1958
* The effect of satellite and aircraft data on Reanalysis (pdf)
* Detailed summary of observational data used by Reanalysis.
* Background error used by the assimilation system (SSI).


The future plans for Reanalysis are to do a regional Reanalysis for the USA. Comments from potential users are wanted.

Feb 5 1999: Jan. 1999 CDAS is being rerun. A change in buffer table caused the GOES not to be used.

Problems with March 1997-December 1997 reanalyses were found which will require a rerun of the affected months. The problem is with the inclusion of too much Indian station data. More details are available.

Problems with aircraft winds used for 1976-1978 were discovered and the rerun was completed Jan 8, 1997. The aircraft data were transposed E-W which reduced the anomaly correlation by 5 points in a 5 day forecast. The effect of this bad jet-level data should be less severe in the lower troposphere. This web site will have the updated data after an examination and the Phoenix AMS meeting.

The "final" TOGA-COARE (Nov92-Feb93) analysis still needs to be rerun. The data on this web server is an interim analysis which doesn't use the TOGA-COARE data. Tapes from NCAR and CDC was well as the annual CD-ROMs contain the first version which is cold over the TOGA-COARE region.

pre-QC observations counts are now available.

IBM/SP CDAS: Starting with May 1, 2000 Analyses causes changes.

Things are not perfect . . . Problem Report:

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