The Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2)

TLDR

The Modern‑Era Retrospective Analysis for Research and Applications, version 2 (MERRA‑2), is NASA’s latest atmospheric reanalysis of the modern satellite era produced by the Global Modeling and Assimilation Office. This paper provides an overview of MERRA‑2 and its performance metrics, aiming to address MERRA’s limitations and serve as a milestone for the future integrated Earth system analysis (IESA) at GMAO. MERRA‑2 updates the GEOS model, assimilates new observation types, began production in June 2014 with four streams converging to a single near‑real‑time stream by mid‑2015, and its products are available online via the NASA Goddard Earth Sciences Data Information Services Center. MERRA‑2 improves aerosol, stratospheric ozone, and cryospheric representations, reduces spurious trends and biases in the water cycle compared to MERRA, and identifies remaining deficiencies.

Abstract

The Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), is the latest atmospheric reanalysis of the modern satellite era produced by NASA’s Global Modeling and Assimilation Office (GMAO). MERRA-2 assimilates observation types not available to its predecessor, MERRA, and includes updates to the Goddard Earth Observing System (GEOS) model and analysis scheme so as to provide a viable ongoing climate analysis beyond MERRA’s terminus. While addressing known limitations of MERRA, MERRA-2 is also intended to be a development milestone for a future integrated Earth system analysis (IESA) currently under development at GMAO. This paper provides an overview of the MERRA-2 system and various performance metrics. Among the advances in MERRA-2 relevant to IESA are the assimilation of aerosol observations, several improvements to the representation of the stratosphere including ozone, and improved representations of cryospheric processes. Other improvements in the quality of MERRA-2 compared with MERRA include the reduction of some spurious trends and jumps related to changes in the observing system and reduced biases and imbalances in aspects of the water cycle. Remaining deficiencies are also identified. Production of MERRA-2 began in June 2014 in four processing streams and converged to a single near-real-time stream in mid-2015. MERRA-2 products are accessible online through the NASA Goddard Earth Sciences Data Information Services Center (GES DISC).