![]() Historically, atmospheric reanalyses have been produced by meteorological centres and upper-level products consisting mainly of temperature, winds, humidity, geopotential height and ozone. BRAM2 is publicly available and will be extended to assimilate MLS observations after 2017.Īn atmospheric reanalysis is an estimation of the past atmospheric state using the information provided by an atmospheric numerical model and a set of observations combined by a data assimilation system. The reanalysis also reveals a drift in MLS N 2O against independent observations, which highlights the potential use of BRAM2 to estimate biases between instruments. Moreover, in the upper troposphere, comparison of BRAM2 with MLS and independent observations suggests a positive bias in MLS O 3 and a negative bias in MLS H 2O. MLS ozone profiles display unphysical oscillations in the tropical UTLS, which are corrected by the assimilation, allowing a good agreement with ozonesondes. pressures lower than) 4 hPa due to a model bias that cannot be corrected by the assimilation. In particular, ozone is not assimilated at altitudes above (i.e. In general BRAM2 reproduces MLS observations within their uncertainties and agrees well with independent observations, with several limitations discussed in this paper (see the summary in Sect. These regions are (1) the lower-stratospheric polar vortex where O 3, H 2O, N 2O, HNO 3, HCl and ClO are evaluated (2) the upper-stratospheric–lower-mesospheric polar vortex where H 2O, N 2O, HNO 3 and CO are evaluated (3) the upper troposphere–lower stratosphere (UTLS) where O 3, H 2O, CO and CH 3Cl are evaluated and (4) the middle stratosphere where O 3, H 2O, N 2O, HNO 3, HCl, ClO and CH 3Cl are evaluated. The evaluation is carried out in four regions of interest where only selected species are evaluated. They are evaluated using independent observations from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS), the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) and N 2O observations from a different MLS radiometer than the one used to deliver the standard product and ozonesondes. ![]() Vertical profiles of eight species from MLS version 4 are assimilated and are evaluated in this paper: ozone ( O 3), water vapour ( H 2O), nitrous oxide ( N 2O), nitric acid ( HNO 3), hydrogen chloride (HCl), chlorine oxide (ClO), methyl chloride ( CH 3Cl) and carbon monoxide (CO). This reanalysis is called BRAM2 for BASCOE Reanalysis of Aura MLS, version 2. The model resolution is 3.75 ∘ in longitude, 2.5 ∘ in latitude and 37 vertical levels from the surface to 0.1 hPa with 25 levels above 100 hPa. BASCOE is based on the ensemble Kalman filter (EnKF) method and includes a chemical transport model driven by the winds and temperature from the ERA-Interim meteorological reanalysis. This reanalysis is produced by the Belgian Assimilation System for Chemical ObsErvations (BASCOE) constrained by the chemical observations from the Microwave Limb Sounder (MLS) on board the Aura satellite. This paper presents a reanalysis of the atmospheric chemical composition from the upper troposphere to the lower mesosphere from August 2004 to December 2017.
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