CESM Models

CCSM2.0 Observational Data Atmosphere Model v5.0 (latm5) Documentation



The CCSM Observational Data Atmosphere Model, version 5.0 (latm5), was released on May 17, 2002, as part of the CCSM2.0 release.

Warning: The version of latm released with CCSM2.0 is provided as an example of how one group of users altered the datm5 source code to cycle through different types of input data streams. This version of latm5 is configured to use only NCEP datasets, and the biases in these data produce solutions that are not of high scientific quality.


User Documents: Combined User's Guide, Source Code Reference, and Scientific Description [html] [pdf]

What is a "data atmosphere model"?

box diagramCCSM coupled model is based on a framework which divides the complete climate system into component models connected by a coupler. This design requires four component models -- atmosphere, sea-ice, land, and ocean -- each connected to the Coupler, and each exchanging data with the Coupler only.

The latm5 Observational Data Atmosphere Model functions as the atmosphere component in a CCSM configuration. The latm5 atmosphere component interacts with the Coupler just like any atmosphere model would, but it is not an active model, rather, it takes atmosphere data from input data files and sends it to the Coupler, ignoring any forcing data received from the Coupler. Typically the input data files contain climatological or time averaged observational data, although some data fabrication is usually necessary as it's unlikely that real world observations exists for all the required fields. Such a "dummy" atmosphere model is useful for doing ocean + ice spinup runs.

This latm5 code is a variant of the datm5 code, the difference being that the datm5 cycles thru daily average data fields normally created by the CCSM active atmosphere component (CCM, now called CAM), while the latm5 cycles thru data from other sources (for example NCEP). The latm5 cycles thru separate data file streams for atmospheric states, precipitation, and radiation. Further, these three data streams can have different sampling intervals, for example, radiation data can be daily average data while precipitation data is monthly average data. Note that the version of latm5 released with CCSM2.0 can only use NCEP data for all three data streams and that the biases in these data will produce solutions that are not of high quality. Improvements to the solutions can be obtained by using better forcing data.

Important note: When assembling a CCSM configuration, carefully consider the limitations and requirements of all components and be sure that the complete set of component models will interact in a meaningful way. In particular, consider whether the data provided by this model is adequate for your application.