First simultaneous global measurements of nighttime stratospheric NO2 and NO3 observed by Global Ozone Monitoring by Occultation of Stars (GOMOS)/Envisat in 2003

Abstract

The Global Ozone Monitoring by Occultation of Stars (GOMOS) stellar occultation instrument on board the Envisat European satellite provides global coverage of ozone and other stratospheric species with good vertical resolution and a self‐calibrating method. In this paper we present the first simultaneous global distribution of stratospheric NO2 and NO3 from 1 year of nighttime GOMOS data in 2003. Most previous NO2 satellite observations have been made using the solar occultation technique. They are difficult to interpret due to the fast photochemical evolution of NO2 at sunrise and sunset. There are no published observations of NO3 from space because this constituent is rapidly photodissociated during daytime and is not observable by solar occultation. It is shown that the NO2 mixing ratio reaches a maximum around 40 km with values between 14 and 16 ppbv at low and middle latitudes. The global distribution of NO2 observed by GOMOS is very similar to the NO + NO2 Halogen Occultation Experiment climatology deduced from sunset measurements from 1999 to 2004. At high latitude a high mixing ratio is observed in the north vortex in November 2003 after a strong solar proton event and in the south vortex in July 2003. The NO3 mixing ratio peaks at 40–45 km. NO3 follows a semiannual variation at low latitudes with maxima at equinoxes and an annual variation at middle and high latitudes with a maximum in summer. In the upper stratosphere the mixing ratio of NO3 is strongly correlated with temperature due to the thermal dependence of its formation rate.