Evaluation of Ozone Analyses From UARS MLS Assimilation by BASCOE Between 1992 and 1997

We present the analyses of UARS MLS ozone data obtained by the Belgian Assimilation System for Chemical ObsErvations (BASCOE). This system, based on the 4D-var method, is dedicated to the assimilation of stratospheric chemistry observations. It uses a 3-D Chemical Transport Model (3D-CTM) including 57 chemical species with explicit calculation of stratospheric chemistry. The CTM is driven by ECMWF ERA-40 analyses of winds and temperature, with a horizontal grid of 3.75 in latitude by 5 in longitude, and with 37 pressure levels from the surface to 0.1 hPa. BASCOE has assimilated UARS MLS observations acquired during the period 1992-1997. We discuss how BASCOE is able to reproduce MLS data, and we evaluate the BASCOE analyses with respect to independent observations from UARS HALOE, ozonesondes, and ground-based lidars. An excellent agreement is found with independent observations (bias usually less than 10%), except in the lowermost stratosphere and in the Antarctic ozone hole. The performances of BASCOE ozone analyses are also compared to those of two other long-term ozone reanalyses; namely, ERA-40 and ERA-Interim, both from ECMWF. Finally, sensitivity test based on BASCOE free model runs suggest that ozone analyses during the ozone hole period would be greatly improved by driving BASCOE with the dynamical fields of the new ECMWF reanalyses ERA-Interim. This work is part of the Stratospheric Ozone Profile Record service raised by the GMES Service Element PROMOTE.