Quantification of the chemical ozone loss in the northern and southern polar vortices using SCIAMACHY limb measurements

Abstract

This study deals with the retrieval of stratospheric and lower mesospheric ozone profiles from satellite observations of limb--scattered solar radiation with SCIAMACHY on the Envisat satellite. The retrieval combines spectral information in the Chappuis and Hartley absorption bands of ozone and employs the SCIATRAN radiative transfer model. The retrieved ozone profiles are applied into two aspects.First, the sensitivity of the ozone profile retrieval to tropospheric clouds is examined using the SCIATRAN radiative transfer model. The considered clouds are vertically and horizontally homogeneous. An aerosol-free atmosphere and Mie phase functions for cloud particles are assumed. Neglecting clouds in the retrieval, the relative errors of ozone profile retrievals in a cloudy atmosphere are computed. The cloud sensitivity of the limb ozone retrievals is significant in the Chappuis bands at lower stratospheric altitudes. The relative error in the retrieved ozone concentrations gradually decreases with increasing altitude and becomes negligible above approximately 40 km. Cloud optical thickness, ground albedo and solar zenith angle have a large impact on the ozone retrievals. For a given cloud optical thickness value, clouds with different geometrical thicknesses or different cloud altitudes have a similar impact on the ozone retrievals, if the clouds are outside the field of view of the instrument. The effective radius of water droplets and the solar azimuth angle has a small influence on the error. Neglecting clouds in the ozone profile retrievals generally leads to a low bias. For the most frequent cloud types, the total error is below 6% above 15 km altitude, if clouds are completely neglected in the retrieval. Second, the stratospheric and lower mesospheric ozone profile data set of SCIAMACHY measurements of limb-scattered solar radiation in the period 2002-2009 is used to determine the chemical ozone loss in both the Arctic and Antarctic polar vortices using the vortex average method. The vortex boundary is determined with a potential vorticity (PV) criterion applied to UKMO stratospheric analyses. The chemical ozone loss at the 450-600 K isentropic levels is derived from the difference between observed ozone abundances and the ozone modelled considering diabatic cooling, but no chemical ozone loss. The results show accumulated chemical ozone losses of up to 20-40% between the beginning of January and the end of March inside the Arctic polar vortex. Strong interannual variability of the Arctic ozone loss is observed, with the cold winters 2005 and 2007 showing the largest chemical ozone losses. The ozone loss in the southern polar vortex does not change much from year to year. At the 475 K isentropic level total relative ozone losses of 70-80% between mid-August and mid-November are observed every year inside the vortex, even in the anomalous year 2002. SCIAMACHY mesurements of polar stratospheric clouds and the chemical ozone loss inside polar vortex are in good agreement.Comparisons of the vertical variation of ozone loss derived from SCIAMACHY observations with several independent techniques for the northern hemisphere winter 2004/2005 show very good agreement.