Accounting for the effect of horizontal gradients in limb measurements of scattered sunlight

• Main Authors: Pu??te, J., Kühl, S., Deutschmann, T., Platt, U., Wagner, T.
• Other Authors: Max Planck Institute for Chemistry (MPIC), Max-Planck-Gesellschaft, Institute of Atomic Physics and Spectroscopy, University of Latvia (LU), Institute of Environmental Physics Heidelberg (IUP), Universität Heidelberg Heidelberg = Heidelberg University
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2007
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Arctic
• Online Access: https://hal.science/hal-00303178; https://hal.science/hal-00303178/document; https://hal.science/hal-00303178/file/acpd-7-16155-2007.pdf

International audience Limb measurements provided by the SCanning Imaging Absorption spectrometer for Atmospheric CHartographY (SCIAMACHY) on the ENVISAT satellite allow retrieving stratospheric profiles of various trace gases on a global scale, among them BrO for the first time. For limb observations in the UV/VIS spectral region the instrument measures scattered light with a complex distribution of light paths: the light is measured at different elevation angles and can be scattered or absorbed in the atmosphere or reflected by the ground. By means of spectroscopy and radiative transfer modelling the measurements can be inverted to retrieve the vertical distribution of stratospheric trace gases. A full spherical 3-D Monte Carlo radiative transfer model "Tracy-II" is applied in this study. The Monte Carlo method benefits from conceptual simplicity and allows realizing the concept of full spherical geometry of the atmosphere and also its 3-D properties, which is important for a realistic description of the limb geometry. Furthermore it allows accounting for horizontal gradients in the distribution of trace gases. In this study the effect ofhorizontal inhomogeneous distributions of trace gases on the retrieval of profiles from limb measurements of scattered UV/VIS light is investigated. We introduce a method to correct for this effect by combining consecutive limb scanning sequences and utilizing the overlap in their measurement sensitivity regions. It is found that if horizontal inhomogenity is not properly accounted for, typical errors of 20% for NO 2 and up to 50% for OClO around the altitude of the profile peak can arise for measurements close to the Arctic polar vortex boundary in boreal winter.