Determination of optical and microphysical properties of volcanic stratospheric aerosols from MIPAS-B limb emission spectra

摘要

Abstract: High resolution limb emission spectra were measured by the balloon-borne FTIR spectrometer MIPAS-B in the Arctic vortex in March 1992. These spectra are significantly affected by the Mt. Pinatubo stratospheric aerosol. A method has been developed for separating the radiance signal of emission lines of trace gases from the aerosol continuum. By applying this method to the MIPAS-B spectra aerosol extinction coefficients have been retrieved at approximately 60 spectral positions in the 750-980 cm$+$MIN@1$/ and 1180-1380 cm$+$MIN@1$/ spectral ranges. The spectral shape of the mid- IR aerosol extinction has been derived for the tangent altitudes 11.3 km, 14.5 km and 16.1 km. On the basis of Mie- calculations it has been demonstrated that the spectral aerosol extinction coefficient is sensitive to the aerosol composition as well as to the particle size distribution. An algorithm has been developed to retrieve microphysical parameters by least-squares fitting of the derived spectral extinction coefficients to Mie-generated extinction coefficients. The retrieved aerosol parameters indicate the significance of scattering even in the mid-IR. Related corrections on the basis of multiple scattering calculations were performed. Retrieved compositions and effective volume densities of the Pinatubo aerosol in the Arctic vortex are presented. !13