Validation of the self-consistency of GOMOS NO₃ , NO₂ and O₃ data using chemical data assimilation

International audienceThe NO3 measurement by the GOMOS instrument on board the ENVISAT platform is the first satellite measurements of this species. The simultaneous measurements of O3 and NO2 , which are strongly coupled chemically to NO3 , allow us to test the self-consistency of the GOMOS measurements of the different species. In this paper, the self-consistency of the nighttime measurements by GOMOS of O3 , NO2 and NO3 are tested using chemical data assimilation. Measurements obtained between 25 and 55 km during two distinct periods are assimilated. Analyzed NO3 (i.e., NO3 calculated by the model after assimilation of GOMOS O3 and NO2 data) are then compared to corresponding GOMOS NO3 measurements in correlation plots (GOMOS NO3 versus analyzed NO3). Overall, the differences between the NO 3 measurements and corresponding analyzed NO 3 are found to be small, about 10% on average. The linear regressions for both periods are also found to be close to the 1-to-1 line with small standard errors. This agreement indicates that O3 , NO2 and NO3 GOMOS measurements are self consistent chemically and that there is no substantial bias in GOMOS NO 3 data. It also suggests that the nighttime NO3 chemistry is well understood