M2‐SCREAM: A Stratospheric Composition Reanalysis of Aura MLS Data With MERRA‐2 Transport.

The MERRA‐2 Stratospheric Composition Reanalysis of Aura Microwave Limb Sounder (M2‐SCREAM) is a new reanalysis of stratospheric ozone, water vapor, hydrogen chloride (HCl), nitric acid (HNO3) and nitrous oxide (N2O) between 2004 and the present (with a latency of several months). The assimilated fields are provided at a 50‐km horizontal resolution and at a three‐hourly frequency. M2‐SCREAM assimilates version 4.2 Microwave Limb Sounder (MLS) profiles of the five constituents alongside total ozone column from the Ozone Monitoring Instrument. Dynamics and tropospheric water vapor are constrained by the MERRA‐2 reanalysis. The assimilated species are in excellent agreement with the MLS observations, except for HNO3 in polar night, where data are not assimilated. Comparisons against independent observations show that the reanalysis realistically captures the spatial and temporal variability of all the assimilated constituents. In particular, the standard deviations of the differences between M2‐SCREAM and constituent mixing ratio data from The Atmospheric Chemistry Experiment Fourier Transform Spectrometer are much smaller than the standard deviations of the measured constituents. Evaluation of the reanalysis against aircraft data and balloon‐borne frost point hygrometers indicates faithful representations of small‐scale structures in the assimilated water vapor, HNO3 and ozone fields near the tropopause. Comparisons with independent observations and a process‐based analysis of the consistency of the assimilated constituent fields with the MERRA‐2 dynamics and with large‐scale stratospheric processes demonstrate the utility of M2‐SCREAM for scientific studies of chemical and transport variability on time scales ranging from hours to decades. Analysis uncertainties and guidelines for data usage are provided. Plain Language Summary: Earth's stratosphere contains a number of trace gases of various origins, chemical properties and lifetimes. In addition to their importance for stratospheric chemistry, including that affecting the ozone layer, and for the planet's radiative budget, the complex geographical and vertical distributions of atmospheric constituents provide invaluable information about stratospheric dynamics and transport in a changing climate. This paper introduces and evaluates a new high‐resolution composition data set produced at NASA's Global Modeling and Assimilation Office. Named the MERRA‐2 Stratospheric Composition Reanalysis of Aura Microwave Limb Sounder (M2‐SCREAM), this stratosphere‐focused product consists of assimilated global three‐dimensional ozone, water vapor, hydrogen chloride, nitric acid, and nitrous oxide fields, all of which are of primary importance to stratospheric chemistry and transport studies. M2‐SCREAM uses high quality data from the Microwave Limb Sounder instrument (2004‐present) combined with meteorological information from NASA's MERRA‐2 reanalysis. Comparisons with independent observations and a process‐based analysis of the consistency of the assimilated constituent fields with the MERRA‐2 dynamics and with large‐scale stratospheric processes demonstrate the utility of M2‐SCREAM for scientific studies of chemical and transport variability on time scales ranging from hours to decades. Key Points: A new composition reanalysis of the stratosphere is introducedMicrowave Limb Sounder ozone, H2O, HNO3, HCl, and N2O are assimilated for 2004–2021 and will be extended to the presentThe reanalysis is useful for studies of chemical and transport variability on time scales from hours to decades [ABSTRACT FROM AUTHOR]