Stratospheric modelling

Background information

The Earth Observing System (EOS) Microwave Limb Sounder (MLS) is one of four instruments on the NASA's EOS Aura satellite, launched on July 15, 2004 (see more information about Aura's here). MLS makes measurements of atmospheric composition, temperature, humidity and cloud ice that are needed to (1) track stability of the stratospheric ozone layer, (2) help improve predictions of climate change and variability, and (3) help improve understanding of global air quality.

In addition to the operational analysis of MLS by BASCOE, available since 2009, the BASCOE Reanalysis of Aura MLS, version 2 (BRAM2) provides analyses since September 2004 when MLS starts to deliver. BRAM2 is obtained by the EnKF version of BASCOE and is driven by ERA-Interim wind and temperature fields provided by ECMWF. The horizontal resolution of BRAM is 3,75° in longitude and 2,5° in latitude. The vertical domain is from the surface to 0.1 hPa resolved by 37 levels (25 levels above 100 hPa) which are a subset of the 60 levels of ERA-Interim. The output frequency is 6 hours. BRAM2 description and its evaluation against independent observations are provided in Errera et al., ACP, 2019 (

BRAM2 assimilates MLS profiles of O3, H2O, N2O, HNO3, HCl, ClO, CH3Cl and CO, i.e. the MLS species that do not need to be averaged before scientific use. BRAM2 outputs are the abundance of assimilated species as well as Cl2O2. Also provided is the variability of the abundance of the species calculated from the standard deviation of the ensemble state of the EnKF system (not available for Cl2O2). The dataset is provided in NetCDF-CF files with one file per year and per constituents. Constituents abundance is given in volume mixing ratio (vmr or mol/mol) on the hybrid pressure grid of BASCOE with a frequency of 6 hours. To allow conversion of vmr to number density and/or transforming the vertical pressure grid into geopotential height, the ERA-Interim temperature and the Earth geopotential at the same resolution of BRAM2 are also available.

More information about BRAM2 can be found in Errera et al., 2019 (

Access to BRAM2

Please, register to receive login and password accessing the BRAM2 dataset on the BIRA-IASB ftp server:



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5-Jul-2022: BRAM2 extended to Aug 2019, i.e. the last date where ERA-Interim was produced. Since BRAM1 is now obsolete, all information on BRAM1 has been removed from the website.

28-Sep-2018: BRAM2 officialy released.

12-Sep-2018: BRAM1 replaced by BRAM-2 on the ftp server.

5-May-2017: BRAM1 Dataset available via ftp.

18-Apr-2017: Web page open to public. Dataset not yet available.