Retrieval of stratospheric aerosol density profiles from SCIAMACHY limb radiance measurements in the O 2 A-band

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Abstract

In this paper we present an approach to retrieve stratospheric aerosol number densities in the altitude range 10-40 km from SCIAMACHY limb radiance measurements in the spectral range of the O 2 A absorption band, near 760 nm. Here, the characteristic light paths differ for the measured light in the O 2 A-band and in the spectral continuum next to the absorption band. This difference is used to distinguish the effect of stratospheric aerosol scattering and ground reflection on the limb measurement. The capability to disentangle both effects is illustrated for SCIAMACHY limb observations over the Libyan desert, where the measurements are not affected by tropospheric clouds. Comparison of the SCIAMACHY retrieval and the SAGE II aerosol extinction product between 75° southern and northern latitude shows the clear need for prior knowledge of the mean size of the stratospheric aerosol for the SCIAMACHY retrieval. We found best agreement between SCIAMACHY and SAGE II aerosol extinction for the period 2003-2005 for a prior choice of the mean aerosol size radius of 0.2 μ4m. The overall agreement between both data sets is in the range <50% root mean square difference at 14-30 km with a minimum of 30% at 22 km.

Figures

  • Fig. 1. Two relevant light paths for limb observations in the longwave visible and near infrared. The effect of multiple atmospheric scattering is not presented.
  • Fig. 2. SCIAMACHY limb radiance measurements at 500 nm over the Libyan desert for tangent height of 25 km as a function of time (black solid line). The Figure shows also three different model simulations using the solar and viewing geometry of the limb observations: for only Rayleigh scattering and no surface reflection (red dashed line), for only Rayleigh scattering and a Lambertian surface albedo of 0.30 (green dotted line), for Rayleigh and background aerosol scattering and a Lambertian surface albedo of 0.30 (blue solid line).
  • Fig. 3. Profile of aerosol particle density adopted from Loughman et al. (2004). The upper anel shows the stratospheric part of the profile and lower panel the tropospheric part. The profile refers to a background load of stratospheric aerosol.
  • Fig. 4. Differences between monthly mean SCIAMACHY radiances and model simulations (measurement – simulation) as a function of tangent height for December (left panel) and June (right panel) for the period 2004–2009. The model configurations are the same as in Fig. 2.
  • Fig. 5. SCIAMACHY limb radiance measurements in the O2 A-band normalized to the radiance at 758 nm for different tangent heights. The vertical lines indicate the wavelengths used in the retrieval.
  • Fig. 6. Stratospheric aerosol density retrieval over the Libyan desert. Dots indicate individual measurements while the solid line represents a one month running mean. (First panel) Aerosol density at 25 km retrieved from SCIAMACHY limb radiance measurements in the O2 A-band. (Second panel) Lambertian surface albedo retrieved at 500 nm. (Third panel) Black sky albedo as a function of time due to its underlying dependence on solar zenith angle as proposed by Briegleb et al. (1986) (red dots) and Wang et al. (2005) (blue dots). (Fourth panel) SCIAMACHY limb radiance measurements at 500 nm at the tangent height closest to 25 km (blue) and forward simulations (red) using the retrieved aerosol profile and the fitted Lambertian surface albedo at 500 nm. (Fifth panel) Relative differences between measurements and simulations.
  • Fig. 7. (left panel) Relative contribution of the emission signal Iemis to a SCIAMACHY limb radiance measurements for a representative retrieval over the Libyan Desert. The emission signal is estimated as described in Sect. 4. (right panel) Effect on the aerosol retrieval when atmospheric emission is neglected in the retrieval. Here, drefaer is the retrieved aerosol density when emission is added to the measurement simulations and daer is the retriev d a rosol density when emission is ignored.
  • Fig. 8. Spatially and temporally co-located SAGE II and SCIAMACHY aerosol extinction profile at 525 nm above China, 3 January 2003. The SAGE II extinction profile are calculated from SAGE II aerosol density and radius profiles. The SCIAMACHY extinction profile is determined in the same way.

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CITATION STYLE

APA

Ovigneur, B., Landgraf, J., Snel, R., & Aben, I. (2011). Retrieval of stratospheric aerosol density profiles from SCIAMACHY limb radiance measurements in the O 2 A-band. Atmospheric Measurement Techniques, 4(11), 2359–2373. https://doi.org/10.5194/amt-4-2359-2011

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