Abstract
Abstract. The Arctic winter 2010/2011 was characterized by a persistent vortex with extremely low temperatures in the lower stratosphere above northern Scandinavia leading to a strong activation of chlorine compounds (ClOx) like Cl, Cl2, ClO, ClOOCl, OClO, and HOCl, which rapidly destroyed ozone when sunlight returned after winter solstice. The MIPAS-B (Michelson Interferometer for Passive Atmospheric Sounding) and TELIS (TErahertz and submillimeter LImb Sounder) balloon measurements obtained in northern Sweden on 31 March 2011 inside the polar vortex have provided vertical profiles of inorganic and organic chlorine species as well as diurnal variations of ClO around sunrise over the whole altitude range in which chlorine has been undergoing activation and deactivation. This flight was performed at the end of the winter during the last phase of ClOx deactivation. The complete inorganic and organic chlorine partitioning and budget for 31 March 2011, assumed to be representative for the late-winter Arctic stratosphere, has been derived by combining MIPAS-B and TELIS simultaneously observed molecules. A total chlorine amount of 3.41 ± 0.30 parts per billion by volume is inferred from the measurements (above 24 km). This value is in line with previous stratospheric observations carried out outside the tropics confirming the slightly decreasing chlorine amount in the stratosphere. Observations are compared and discussed with the output of a multi-year simulation performed with the chemistry climate model EMAC (ECHAM5/MESSy Atmospheric Chemistry). The simulated stratospheric total chlorine amount is in accordance with the MIPAS-B/TELIS observations, taking into account the fact that some chlorine source gases and very short-lived species are not included in the model.
Highlights
The discovery of the Antarctic stratospheric “ozone hole” in the 1970s (Farman et al, 1985) strongly intensified research to unravel the reason for this ozone depletion
In EMAC, the subsidence of the air masses in the course of the winter was underestimated such that we find higher values of tracers like N2O and CFCs at a given altitude of the lower stratosphere compared to the measurements
Observations from MIPAS-B/TErahertz and submillimeter LImb Sounder (TELIS) were performed at the end of the cold 2010/2011 stratospheric winter that was characterized by a persistent polar vortex enabling strong chlorine activation and ozone loss
Summary
The discovery of the Antarctic stratospheric “ozone hole” in the 1970s (Farman et al, 1985) strongly intensified research to unravel the reason for this ozone depletion. The long term trend of stratospheric inorganic chlorine was investigated by using data of multiple space-borne sensors like ACE-FTS, ATMOS, MLS, CLAES (Cryogenic Limb Array Etalon Spectrometer), CRISTA (CRyogenic Infrared Spectrometer and Telescope for the Atmosphere), and HALOE (Lary et al, 2007). This time series confirms that stratospheric Cly peaked in the late 1990s and started to decrease as expected due to the changing concentrations of tropospheric source gases and related transport times from the troposphere to the stratosphere.
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