FAQ - WDCC / CERA User Interface & Download


General support

If you experience problems or need assistance please send an email to . A ticketing system will acknowlegde your enquiry and generally your request will be processed within one working day. When sending attachments (i.e. screenshots) please bear in mind that the ticketing system will only accept mails up to 3MB in size.

For an overview of the current status of the WDCC's services please visit http://wdcc-status.dkrz.de/.

Accounts & Password

How do I get access to the CERA database?
Please fill out the form at https://cera-www.dkrz.de/WDCC/ui/cerasearch/register or send an email containing your name and institute affiliation to . You will receive the account details when your request has been processed (usually within one working day).
How can I reset a lost password?
Please contact  to reset your password.
How can I change my password?
The password can be changed after login on this page: https://cera-www.dkrz.de/WDCC/ui/ManagePassword.jsp.

Data usage

How is the data licensed?
All data and pages available from WDCC are licensed under a Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/2.0/de/deed.en) as far as those conditions are not in any way modified by the following conditions or by any conditions specific to data or pages. For more detail see 'Conditions WDCC Database':http://terms.wdc-climate.de/
How to cite data?
Citation information can be found via webbrowser using the CERA user interface (http://cera.wdc-climate.de/):
  • Enter the name or acronym of the CERA data object into the search box and click on the magnifying glass
  • Click the blue label (e.g. 'experiment' or 'dataset group') in the result list
  • The citation information can be found in the 'Cite this data' block of the metadata page
Citation examples:
  • Experiment citation on http://cera-www.dkrz.de/WDCC/ui/Compact.jsp?acronym=MODIS__Arctic__MPF_V02
    Rösel, Anja; Kaleschke, Lars; Kern, Stefan (2015): Gridded Melt Pond Cover Fraction on Arctic Sea Ice derived from TERRA-MODIS 8-day composite Reflectance Data bias corrected Version 02. World Data Center for Climate. doi:10.1594/WDCC/MODISArcticMPF_V02
  • Dataset group citation on http://cera-www.dkrz.de/WDCC/ui/Compact.jsp?acronym=NCCNMhg Bentsen,Mats; Bethke,Ingo; Debernard,Jens; Drange,Helge; Heinze,Christoph; Iversen,Trond; Kirkevåg,Alf; Seland,Øyvind; Tjiputra,Jerry (2012): cmip5 output1 NCC NorESM1-M historicalGHG, served by ESGF. World Data Center for Climate. doi:10.1594/WDCC/CMIP5.NCCNMhg
For more information see also: http://www.komfor.net/cite-data.html

Data download in general

How can I access data stored in the CERA database?
CERA datasets can either be downloaded via webbrowser using the CERA user interface or with the Java-based commandline tool Jblob that can be used on any OS supporting Java ( Oracle or OpenJDK ).
Is it possible to select temporal subsets during data download?
Both the CERA web interface and Jblob generally offer the ability to select temporal subsets of stored data by specifying start and end dates. The granularity is based on how the data is stored in our database, e.g. the smallest downloadable time span for a dataset that is stored in monthly records is one month.
Is it possible to select a geographic region during data download?
Jblob offers a subset of cdo processing capabilities, including selection of a geographic region, please take a look at the Jblob documentation for more information. Regional selection from the interactive download is currently not possible.
Can the data format be changed during download (i.e. Grib => NetCDF)?
Currently it is not possible to change a dataset's format during download.
Can wget be used to download data from CERA?
Wget access is currently not supported.
What is the maximum size of downloads?
Currently a maximum of 16TB can be downloaded or selected for processing in a single request.
Can I get more information about the datasets stored within the CERA database?
For many datasets supplementary information is available in the form of "additional_info"-type entries (these can be found in the data hierarchy) or individually stored detailed data headers. The data headers (if available) can be accessed from the dataset's metadata information page by clicking on the "Data headers" button in the 'General information' section.

Data download speed and access times

Why does it take so long before the download actually starts?
A large part of the datasets available from the CERA database are stored on tapes and have to be retrieved to a local disk cache before the actual transfer. Only downloads for datasets that are currently present in the disk cache will start immediately. It is not necessary to start a download again if the first request ist still active but hasn't transferred anything yet.
How long will it take to transfer data stored on tapes?
The tape access delay depends on the current workload of our archive subsystem, usually the transfer from tape to disk cache will start within 5-10 minutes. The transfer speed between tapes and disk cache is 100-120 MB/s. Please keep in mind that datasets in the CERA database are stored within special "containers" that may be larger than the dataset itself, so the transfer of a 1 GB dataset might take longer if it is archived within a 100 GB container. The same applies for downloading temporal subsets of datasets.
How long will it take to process data during download?
Data processing during download currently is done in 3 separate steps. First, the datasets is retrieved from tapes (if necessary) and the selected time steps are merged into a single file. Afterwards the cdo processing will take place and finally the result file will be tranferred to the user. The resulting idle time before the download actually starts may be up to several hours, e.g. when extracting smaller areas or sinlge variables from very large / multi-variable datasets.

CERA user interface

How many parallel downloads can I start?
Please limit the number of parallel downloads to 4. If you need to download large numbers of datasets please take a look at our batch download tool Jblob and create a script for chain-downloads of datasets. Additionally there is a feature available on many list page that allows you to download .csv lists for script generation and/or pre-defined Jblob download scripts.
Are download managers (including browser add-ons) supported?
Download managers are not supported, if you need to use them regardless please configure a retry interval of at least 60 seconds and limit the number of parallel downloads to 4. If usage of a download manager results in too many request in a very short time your account may be temporarily blocked!

Jblob

How many parallel downloads can I start?
Please limit the number of parallel downloads to 4 and the number of processing (cdo) requests to 1 when processing very large datasets.
How do I know if my Jblob download was successful?
Please check the return value of the Jblob call. A return code of 0 is a successful transfer, any other value indicates a problem during data download. Please take a look at the Jblob documentation for a description of the different exit values.
How can I use Jblob on DKRZ's mistral system?
Jblob is accessible on mistral via the module 'jblob', you only need to load the module by executing 'module load jblob' and this will add the binary to your search path and prepare the Java environment.

Common Jblob error messages

cdo(2) sellonlatbox (Abort): Unsupported grid type!

In most cases appending '--cdo "selgridname,gaussian"' to the processing request will avoid the error, e.g.
jblob --dataset <acronym> --cdo "sellonlatbox,0,180,0,90" --cdo "selgridname,gaussian"