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. More information about Aura's science contributions can be found 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, BRAM (BASCOE Reanalysis of Aura MLS) provides analyses since September 2004 when MLS starts to deliver. BRAM 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.

MLS assimilated species are: O3, H2O, N2O, HNO3, HCl, ClO, CH3Cl and CO, i.e. the MLS species that do not need to be averaged before scientific use. BRAM outputs, for Release 2, 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 BRAM are also available.

BRAM release 2 (BRAM2) is available for download since September 18, 2018. This new release benefited on several updates in the BASCOE system: improved PSC scheme, improved solar spectral irradiance datasets, improved EnKF, no more missing outputs (hopefully)... The significant differences between BRAM1 and 2 are:

  • BRAM2 improves HCl and ClO in polar winter, above 30 hPa due to updated setting for aerosols and PSC parameterization.
  • BRAM2 provides the std dev of the ensemble as an estimation of the analysis uncertainties (not provided in BRAM1 because not properly saved during BRAM1 production).
  • BRAM2 extended for 2017.

More details on the differences between BRAM1 and 2 are reported here.

BRAM2 validation is ongoing based on comparison against satellite observations provided by ACEFTSMIPAS (IMK retrieval algorithm) and the Harmoz O3 CCI limb profiles, and comparison against WOUDC ozone sondes (see the poster presented during the SPARC General Assembly 2018). Several presentations and posters have discussed BRAM1 and most of their conclusions remain valid for BRAM2:


Access to BRAM2

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




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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.