Abstract
Abstract. ALTIUS (Atmospheric Limb Tracker for the Investigation of the Upcoming Stratosphere) is the upcoming stratospheric ozone monitoring limb sounder from ESA's Earth Watch programme. Measuring in the ultraviolet–visible–near-infrared (UV–VIS–NIR) spectral regions, ALTIUS will retrieve vertical profiles of ozone, aerosol extinction coefficients, nitrogen dioxide and other trace gases from the upper troposphere to the mesosphere. In order to maximize the geographical coverage, the instrument will observe limb-scattered solar light during daytime (i.e. bright limb observations), solar occultations at the terminator and stellar/lunar/planetary occultations during nighttime. This paper evaluates the constraint of ALTIUS ozone profiles on modelled stratospheric ozone by means of an observing system simulation experiment (OSSE). In this effort, a reference atmosphere has been built and used to generate ALTIUS ozone profiles, along with an instrument simulator. These profiles are then assimilated to provide ozone analyses. A good agreement is found between the analyses and the reference atmosphere in the stratosphere and in the extra-tropical upper troposphere. In the tropical upper troposphere, although providing significant information in the analyses, the assimilation of ozone profiles does not completely eliminate the bias with respect to the reference atmosphere. The impacts of the different modes of observations have also been evaluated, showing that all of them are necessary to constrain ozone during polar winters where solar/stellar occultations are the most important during the polar night and bright limb data are the most important during the development of the ozone hole in the polar spring.
Highlights
Stratospheric ozone (O3) is an essential component of the Earth’s system
It shows the ozone distribution for the nature run on 15 September 2009 at around 44 hPa and the differences between the nature run and the control and assimilation runs
A large part of polar ozone has been destroyed by active chlorine above Antarctica, as shown by the low ozone abundances in the nature run in this region
Summary
Stratospheric ozone (O3) is an essential component of the Earth’s system. By absorbing solar ultraviolet (UV) light in the stratosphere, it protects the Earth’s surface from exposure to harmful radiation (Brasseur and Solomon, 2005). Surface emissions of halogen compounds, whose production has been progressively banned after the implementation of the Montreal Protocol in 1987, are responsible for the reduction of the ozone layer worldwide (WMO, 2018). Emissions of long-lived greenhouse gases may have direct – via the emissions of methane and nitrous oxide – and indirect – via change in atmospheric temperature – effects on the state of the ozone layer (SPARC/IO3C/GAW, 2019). By affecting the thermal structure of the atmosphere, changes in the stratospheric ozone will have an impact on the atmospheric circulation (Hardiman et al, 2014).
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