Remote-sensing measurements in the polar vortex: Comparison to in situ observations and implications for the simultaneous retrievals and analysis of the NO2 and OClO species

Abstract

Nighttime remote-sensing balloon observations conducted by the SALOMON instrument in the arctic polar vortex in January 2006 reveal high amounts of stratospheric NO2 in the lower stratosphere similarly to previously published profiles. NO2 concentration enhancements are also present in the vertical profiles observed by the GOMOS instrument on board the Envisat satellite and obtained coincidently to the balloon measurements. Such quantities are not present in in situ observations obtained by the SPIRALE instrument in similar geophysical conditions. While OClO amounts are acceptably reproduced by Chemistry Transport Model (CTM) calculations, NO2 simulated values are well below the observed quantities. The examination of the slant column densities of NO2 obtained at float altitude highlights unexpected strong enhancements with respect to the elevation angle and displacement of the balloon. It is shown that these fluctuations result from NO2 spatial inhomogeneities located above the balloon float altitude. Potential vorticity maps reveal the presence of midlatitude NP2-rich air in the upper stratosphere or lower mesosphere as a result of the perturbed dynamical situation of the vortex. The presence of spatial inhomogeneities crossed by the lines of sight leads to artificial high concentration values of NO2 in the vertical profile retrieved from the slant column densities assuming spatial homogeneity. A direct implication is that the differences previously observed between measurements of NO2 and OClO and model results are probably mostly due to the improper inversion of NO2 in the presence of perturbed dynamical conditions or when mesospheric NO2 production events occur. The dynamical situation will halve to be systematically analyzed in future studies involving remote-sensing observations. Copyright 2007 by the American Geophysical Union.