Utilizing Increments in Model Development

MERRA data has complete budgets for water and energy, including the incremental analysis updates (IAU) that constrain the model forecast to the analyzed observations. The increments can be interpreted instantaneously (at the six hour analysis) as a representation of the forecast error, or for longer terms as the mean model bias. The magnitude of the IAU terms are not trivial, and should be accounted for, certainly in budget studies, but can also be useful in understanding the representation of weather and climate phenomena in reanalyses.

As an example of utilizing the increments to evaluate the background model, Mapes and Bacmeister (2012) have evaluated MERRA's tropical climate and convection, relating significant IAU values to weaknesses in the representation of physical processes. They suggest diagnostics and potential areas for model development.