Abstract
Abstract. The Optical Spectrograph and InfraRed Imaging System (OSIRIS) onboard the Odin satellite has now taken over a decade of limb scatter measurements that have been used to retrieve the version 5 stratospheric aerosol extinction product. This product is retrieved using a representative particle size distribution to calculate scattering cross sections and scattering phase functions for the forward model calculations. In this work the information content of OSIRIS measurements with respect to stratospheric aerosol is systematically examined for the purpose of retrieving particle size information along with the extinction coefficient. The benefit of using measurements at different wavelengths and scattering angles in the retrieval is studied, and it is found that incorporation of the 1530 nm radiance measurement is key for a robust retrieval of particle size information. It is also found that using OSIRIS measurements at the different solar geometries available on the Odin orbit simultaneously provides little additional benefit. Based on these results, an improved aerosol retrieval algorithm is developed that couples the retrieval of aerosol extinction and mode radius of a log-normal particle size distribution. Comparison of these results with coincident measurements from SAGE III shows agreement in retrieved extinction to within approximately 10% over the bulk of the aerosol layer, which is comparable to version 5. The retrieved particle size, when converted to à ngström coefficient, shows good qualitative agreement with SAGE II measurements made at somewhat shorter wavelengths.
Highlights
Stratospheric aerosols play an important role in Earthâs radiative balance and have been studied using numerous instruments
After Rayleigh scattering and gaseous absorbers are accounted for, aerosol extinction can be computed from the residual signal
As a function of extinction the measurement vectors are well behaved, showing a roughly lin-. Removal of this bias requires more accurate estimation of the particle size parameters used in the SASKTRAN model, and the following section discusses the information available from Optical Spectrograph and InfraRed Imaging System (OSIRIS) to retrieve particle size directly
Summary
Stratospheric aerosols play an important role in Earthâs radiative balance and have been studied using numerous instruments. Satellite limb scatter instruments include the Optical Spectrograph and InfraRed Imaging System (OSIRIS) (Llewellyn et al, 2004), SAGE III (Rault, 2005; Rault and Loughman, 2007), the SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) (Bovensmann et al, 1999) and the Ozone Mapping and Profiler Suite (OMPS) (Rault and Loughman, 2013). These limb scatter instruments measure vertical profiles of integrated line of sight radiance, typically at a wide range of wavelengths from the UV to the near infrared.
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