OClO slant column densities derived from GOMOS averaged transmittance measurements

C Tétard,E Dekemper,G Barrot,C Bingen,D Pieroux,A Dehn,L Saavedra De Miguel,F Dalaudier,O Fanton D'Andon,C Robert,N Mateshvili,A Hauchecorne,D Fussen,J.-L Bertaux,E Kyrölä,F Vanhellemont,L Blanot,V Sofieva,J Tamminen

doi:10.5194/amt-6-2953-2013

Abstract

Abstract. The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the European platform ENVISAT (ENVironment SATellite) was dedicated to the study of the of Earth's atmosphere using the stellar occultation technique. The spectral range of the GOMOS spectrometer extends from the UV (ultra violet) to the near infrared, allowing for the retrieval of species such as O3, NO2, NO3, H2O, O2, air density, aerosol extinction and OClO. Nevertheless, OClO cannot be retrieved using a single GOMOS measurement because of the weak signal-to-noise ratio and the small optical thickness associated with this molecule. We present here the method used to detect this molecule by using several GOMOS measurements. It is based on a two-step approach. First, several co-located measurements are combined in a statistical way to build an averaged measurement with a higher signal-to-noise ratio; then, a differential optical absorption spectroscopy (DOAS) method is applied to retrieve OClO slant column densities (SCD). The statistics of the sets of GOMOS measurements used to build the averaged measurement and the spectral window selection are analyzed. The obtained retrievals are compared to results from two balloon-borne instruments. It appears that the inter-comparisons of OClO are generally satisfying (relative differences are about 15–60%). Two nighttime climatologies of OClO based on GOMOS averaged measurements are presented. The first depicts annual global pictures of OClO from 2003 to 2011. From this climatology, the presence of an OClO SCD peak in the equatorial region at about 35 km is confirmed and strong OClO SCD in both polar regions are observed (more than 1016 cm−2 in the Antarctic region and slightly less in the Arctic region), a sign of chlorine activation. The second climatology is a monthly time series. It clearly shows the chlorine activation of the lower stratosphere during winter. Moreover the equatorial OClO SCD peak is observed during all years without any significant variations. This very promising method, applied on GOMOS measurements, allowed us to build the first nighttime climatology of OClO using limb-viewing instruments.

Highlights

The discovery of the stratospheric ozone depletion in Antarctica by Farman et al (1985) has led to numerous studies to understand the physical and chemical mechanisms involved in this recurrent phenomenon
Chemically inert in the troposphere and are not soluble in water, which make them resistant to washout processes. They are efficiently transported into the stratosphere where they are photolyzed by UV radiation or oxidized to produce atomic chlorine and chlorine monoxide (ClO)
– measurements using balloon-borne instruments allowing the retrieval of the vertical profile of concentration of OClO: Absorption by the Minor components Ozone and NOx (AMON, Renard et al, 1997), and Spectroscopie d’Absorption Lunaire pour l’Observation des Minoritaires Ozone et NOx (SALOMON, Renard et al, 2000). Flights of these two instruments have been used to compare the OClO concentration profiles retrieved from the Global Ozone Monitoring by Occultation of Stars (GOMOS) measurements (Bertaux et al, 2010)

Summary

Introduction

The discovery of the stratospheric ozone depletion in Antarctica by Farman et al (1985) has led to numerous studies to understand the physical and chemical mechanisms involved in this recurrent phenomenon. Flights of these two instruments have been used to compare the OClO concentration profiles retrieved from the Global Ozone Monitoring by Occultation of Stars (GOMOS) measurements (Bertaux et al, 2010).

Results

Conclusion