MERRA, MAC and LandFlux

In a recent paper, Bosilovich et al. (2009) evaluate 8 operational analyses to better assess the uncertainty of the physical fields (not the assimilated states) derived form (re)analysis systems. During the first phase of the Coordinated Enhanced Observing Period (CEOP) 8 international meteorological analyses were collected for a common period, along with supporting satellite and in situ observations. The model data is called the Multi-model Analysis for CEOP (MAC). In general, it was found that the global precipitation and outgoing long wave radiation derived from an ensemble of analyses provided fields that more closely resemble available observations than any one of the members.

For certain physical quantities, such as surface evaporation, a reliable method of observation is not available, and international projects such as SeaFlux and LandFlux are being developed to best fill the gap. In some research, data from analyses and reanalyses are taken as a substituted for observations. The figure below shows the MAC ensemble members compared with the ensemble mean. In places, there is as much as +/- 75 W/m^2 differences among systems. Comparison with such a data set can clearly identify outlying systems. Also, for certain research, using the physical fields from a single system may not be adequate.

Caption: MAC version 2 systems Latent Heat Flux differenced from the ensemble mean for July 2004. Version 2 includes the MERRA and ECMWF ERA Interim reanalyses in addition to the version 1 data. Mean and standard deviation of the difference fields are provided in each panels title.

More information on MAC and the data download are available.

Bosilovich, M.G., D. Mocko, J.O. Roads, and A. Ruane, 2009: A Multimodel Analysis for the Coordinated Enhanced Observing Period (CEOP). J. Hydrometeor., 10, 912–934.