The first dataset was released in 2009 by the NASA Global Modelling and Assimilation Office (GMAO). It is based on a version of the GEOS-51 atmospheric data assimilation system that was frozen in 20082. Due to apparent limitations and deficiencies, the MERRA reanalysis dataset production was completed on February 29, 2016.

By integrating the latest advances in atmospheric modelling and data assimilation, the MERRA-2 program was developed to replace the original MERRA product.

The water cycle was a major consideration during the development of the first data assimilation system. Over time, the use of the original water balance equation showed inconsistencies in terms of mass conservation. This resulted in the need to develop a more reliable model.

The MERRA-2 data assimilation system differs from its predecessor because the data system involves numerous additional observations (mostly satellite data), as well as a preferred cubed-sphere grid, instead of the initial latitude–longitude grid. Additionally, some modifications were brought to the forecast model, as well as the assimilation procedure.

By Perrine Bugeat – Asset Manager