Climate Data Assimilation System

CDAS is based on the Reanalysis data assimilation system and is run in real time. The CDAS analyses along with Reanalysis are used by the Climate Prediction Center (CPC) for climate monitoring. Since the other sources of Reanalysis data (CDC, NCAR, NCDC) are not able to provide the data in a timely manner, a subset of the current CDAS data is available by the Internet. The subset includes monthly and daily averages of many standard pressure-level data and surface flux quantities. We expect (but do not promise) that the data will be updated by the fifth of the month for the preceding month.

While we encourage users to access these data, please understand that the data sets have been constructed to meet the needs of CPC. Our limited resources preclude us from adding extra data fields or making custom data sets. Other CDAS/Reanalysis products can be obtained from the standard data distributors.

FTPing the Data to You

The on-line data can be obtained by filling out a form and having our computer FTP the data to your machine.

Plots of the Data

The on-line data can be displayed using your browser. The plots can be downloaded as postscript files and GrADS metafiles for printing.

Downloading the Data by a Browser

Most of the CDAS data sets have 3 files, the GRIB data, the GrADS index files (*.idx) and GrADS control files (*.ctl). Some data set have a fourth file (*.wgrib.idx) which is a wgrib inventory.

The data can either be obtained by an FTP transfer to your machine (FTP2You) or interactively by Netscape, Mosaic or any reasononable web browers. Unfortunately we are not able offer anonymous FTP access. The directions for the httpd transfer are as follows:

Workstation version of Netscape
press the shift key and use the left mouse button to select the file
download the data as a "source" file.
Workstation version of Mosaic
select "Load to Local Disk" under "Options" menu item
select the file using the left mouse button
Microsoft Explorer v2.0
select file using the right mouse button
select "save target as"
Windows version of Netscape v2
had problems, MS-DOS text conversion?
All users
position cursor over the incomplete filename and the full file name should appear on the bottom of the window

Links to the Data

Information about the data :
Monthly CDAS
Daily CDAS
Reading GRIB
Daily-averaged data:
Daily mean pressure-level data (httpd)
Daily-averaged non-pressure-level data (httpd)
Monthly-averaged data:
Monthly pressure-level data (httpd)
Monthly non-pressure-level data (httpd)
monthly average 00Z (06Z, 12Z, 18Z) pressure-level data
monthly average 00Z (06Z, 12Z, 18Z) non-pressure-level data
Other Methods of Accessing the Data:

The above links will change when a more permanent access method is implemented.

Anonymous FTP

We've being getting complaints about not allowing FTP access. (In a perverse way, we like the complaints. It indicates that people are actually using the data, and we did something right.) We have suggested to higher-ups that resources be put into allowing ftp access.

Questions and Support

Details of Reanalysis/CDAS are explained the March 1996 issue of the Bulletin of the American Meteorology Society (BAMS). Some questions about Reanalysis can be answered by the standard Reanalysis data distributors. and by the various WEB pages about Reanalysis.

The CDAS data is in GRIB, and problems with reading GRIB files are history.

We would have liked to make these files available by FTP but we didn't have an "extra" machine available at the time the system was set up. (We are only allowed to have Anonymous FTP from "non-secure" machines.) We have since received feedback that downloading data by a Netscape (1) can time out and fail, (2) cannot be put into a cron job and (3) is just a pain in the #$?. If you think this situation should be changed, the name of the game is feedback.

If you find that links to the CDAS data are "403 Forbidden" or that "your client does not have permission", please try again later. We probably experienced a power outage and the system-admin people are probably busy trying to fix all the problems. If the problem persists for more than 1.5 days, e-mail: or .

Home Sweet Home

Problems: contact or