Multi-model Analysis for the Coordinated Enhanced Observing Period (CEOP): Evaluating observational analyses and their uncertainties

CEOP is an international working group aiming to better understand the global water and energy cycles through evaluations of data from satellites, models and stations (See The modeling effort has fostered collaboration among international numerical weather prediction centers and also modeling research centers, ultimately leading to the contribution of eight (as of June 2008) operational analyses of the weather during the CEOP (Oct 2002 - Dec 2004). The operational analyses are merged observations data that provide the initial conditions from which numerical weather forecasts are initialized.

It is important to recognize that analyses of the atmospheric state is not observation, and the model influence can lead to significant uncertainty, especially in model physical fields (such as precipitation). The main purpose of the Multi-model Analysis for CEOP (MAC) is to evaluate the uncertainty of the analyses, and to provide a common framework for evaluating many analyses. Further, the analyses do replicate the weather patterns as influenced by the available observations, so, we hypothesize that a linear ensemble average of the will provide a base of comparison for the development of new analyses (providing the variance as well as the mean).

The various model data sets submitted to CEOP were not governed with regards to grid resolutions, time, or variable names. Also, several data days were lost, and not reproduced by some centers. So, the collection of data is not immediately comparable. The MAC project overcame these issues. The method of homogenizing the model data is described in this document (PDF).

Early results have been surprising where the Multi-model ensemble data is statistically closer to some observations than any of the contributing members. Some of the early results were summarized at the AMS Annual meeting. (See

The uniform data developed for MAC has been made available at the Goddard Earth Sciences - Data Information Services Center (GES DISC) at This is the first version of the MAC data set. A second version is planned to include the GMAO GEOS5 system and the ECMWF Interim Reanalysis. Further, suggestions from users regarding this data set may be implemented in version 2.

» Multi-model Analysis for CEOP (MAC) Variable Information Spreadsheet (MS Excel)