Cloud Inhomogeneity and Polarization Effects in Spaceborne Passive mm/sub-mm Observations of Midlatitude Cirrus
Abstract
Probably the greatest uncertainty in future projections of climate arises from clouds ,their interactions with radiation, and their role in the hydrological cycle. Improved observations of the ice water content of clouds and the vertical distribution of these clouds are required to assess and improve the treatment of cloud/radiation interaction and the hydrological cycle in GCMs. Passive mm/sub-mm has some advantages compared to other space-borne cloud-ice remote sensing techniques. With multiple wavelengths chosen from the mm/sub-mm region it is possible to manage the penetration/sensitivity trade-off, and retain sensitivity to part of the particle size distribution that contain most of the cloud ice mass. A complicating factor in using mm/submm wavelengths to observe cirrus, is that the particle/radiation interaction is dominated by scattering. This complicates the radiative transfer (RT) part of the retrieval problem. Scattering introduces polarization and an influence from atmospheric properties outside the line of sight, and hence a requirement of 3D geometry for a complete treatment. In this work we use state-of-the-art radiative transfer model(ARTS-MC), on a detailed midlatitude cirrus scenario, to give simulated observations for three different space-borne instruments: the Advanced Microwave Sounding Unit - B (AMSU-B), the Cloud Ice Water Sub-millimetre Imaging Radiometer (CIWSIR), and the Earth Observing System Microwave Limb Sounder (EOS-MLS). As well as demonstrating the capability of the radiative transfer software to perform such detailed simulations, the results indicate the extent to which cloud inhomogeneity affects the radiances observed by these instruments, and the extent of polarization effects caused by particle shape.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.A51H..07D
- Keywords:
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- 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0319 Cloud optics;
- 0360 Radiation: transmission and scattering;
- 0394 Instruments and techniques