Abstract
Abstract. Recent work has shown that the retrieval of stratospheric aerosol vertical profiles is possible using limb scattered sunlight measurements at optical wavelengths. The aerosol number density profile is retrieved for an assumed particle size distribution and composition. This result can be used to derive the extinction at the measured wavelength. However, large systematic error can result from the uncertainty in the assumed size distribution when the result is used to estimate the extinction at other wavelengths. It is shown in this work that the addition of information obtained from the near infrared limb radiance profile at 1530 nm measured by the imaging module of the OSIRIS instrument yields an indication of the aerosol size distribution profile that can be used to improve the fidelity of the retrievals. A comparison of the estimated extinction profile at 1020 nm with two coincident occultation measurements demonstrates agreement to within approximately 15% from 12 to 27 km altitude.
Highlights
The retrieval of the vertical profile of stratospheric aerosol from limb scatter measurements is of recent interest for the continuation of the long term trend measurements made by past occultation experiments, including the Stratospheric Aerosol and Gas Experiment (SAGE) series (McCormick et al, 1979; Russell and McCormick, 1989; Thomason and Taha, 2003), the Halogen Occultation Experiment (Russell et al, 1993), and the Polar Ozone and Aerosol Measurement (POAM) II and III instruments (Glaccum et al, 1996; Lucke et al, 1999)
Previous studies have shown the potential for the retrieval of stratospheric aerosol parameters from limb scattered radiance profiles
These include methods proposed by Tukiainen et al (2008), which retrieves an aerosol number density from Optical Spectrograph and InfraRed Imaging System (OSIRIS) radiances using a Modified Onion Peel technique and parameterizations of the cross sections and scattering phase functions, and by Rault and Loughman (2007), which uses an optimal estimation technique and Mie scattering phase functions to retrieve multichannel extinction profiles from SAGE III limb scatter measurements
Summary
The retrieval of the vertical profile of stratospheric aerosol from limb scatter measurements is of recent interest for the continuation of the long term trend measurements made by past occultation experiments, including the Stratospheric Aerosol and Gas Experiment (SAGE) series (McCormick et al, 1979; Russell and McCormick, 1989; Thomason and Taha, 2003), the Halogen Occultation Experiment (Russell et al, 1993), and the Polar Ozone and Aerosol Measurement (POAM) II and III instruments (Glaccum et al, 1996; Lucke et al, 1999). When the retrieved aerosol profile is used to forward model the limb et a1l.0, 1989; Bingen et al, 2004)1.0 In this paper, we show that ply at1th0e−725Ns0aummnmbeerrcDea1etnr0ni0sebitvyea, (lacpmtep−c3l)hie1nd0i2qtuoethBe0oluirmasbsE5arxatiedntciatiaonl1n.c0Re(a2pt0ior0o17fi5)leapa-t radiance in the near infrared at 1530 nm, there is a significant difference between the modeled radiance and the IRI measurement This discrepancy is an indication of the error in 1530 nm that is measured by one of the channels of the In- the assumed particle size distribution. Using the Angstrom exponent relation, this can be interpreted as a size distribution corresponding to particles that are too large; that is, in order to make the 1530 nm model prediction agree with the IRI measurements, the aerosol cross section must decrease more quickly with wavelength. For the wavelengths and particle sizes of interest here, the phase function varies relatively slowly with particle size (McLinden et al, 1999)
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