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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/amt-2017-261
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
28 Jul 2017
Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Measurement Techniques (AMT) and is expected to appear here in due course.
Single Footprint Retrievals for AIRS using a Fast TwoSlab Cloud-Representation Model and All-Sky Radiative Transfer Algorithm
Sergio DeSouza-Machado1, L. Larrabee Strow1,2, Andrew Tangborn1, Xianglei Huang3, Xiuhong Chen3, Xu Liu4, Wan Wu5, and Qiguang Yang5 1JCET, University of Maryland Baltimore County, Baltimore, Maryland, USA
2Dept of Physics, University of Maryland Baltimore County, Baltimore, Maryland, USA
3University of Michigan, Ann Arbor, Michigan, USA
4NASA Langley Research Center, Langley, Virginia, USA
5Science and Systems and Applications, Inc, Hampton, Virginia, USA
Abstract. 1D-variational retrievals of temperature and moisture fields from hyperspectral infrared satellite sounders use cloud- cleared radiances as their observation. These derived observations allow the use of clear-sky only radiative transfer in the inversion for geophysical variables but at reduced spatial resolution compared to the native sounder observations. Cloud-clearing can introduce various errors, although scenes with large errors can be identified and ignored. Information content studies show that when using multi-layer cloud liquid and ice profiles in infrared hyperspectral radiative transfer codes, there are typically only 2–4 degrees of freedom of cloud signal. This implies a simplified cloud representation is sufficient for some applications which need accurate radiative transfer. Here we describe a single-footprint retrieval approach for clear and cloudy conditions, which uses the thermodynamic and cloud fields from Numerical Weather Prediction (NWP) models as a first guess, together with a simple cloud representation model coupled to a fast scattering radiative transfer algorithm (RTA). The NWP model thermodynamic and cloud profiles are first co-located to the observations, after which the N-level cloud profiles are converted to two slab clouds (typically one for ice and one for water clouds). From these, one run of our fast cloud representation model allows an improvement of the a-priori cloud state by comparing the observed and model simulated radiances in the thermal window channels. The retrieval yield is over 90 %, while the degrees of freedom correlate with the observed window channel brightness temperature which itself depends on the cloud optical depth. The cloud representation/scattering package is bench-marked against radiances computed using a Maximum Random Overlap cloud scheme. All-sky infrared radiances measured by NASA's Atmospheric Infrared Sounder (AIRS) and NWP thermodynamic and cloud profiles from the European Center for Medium Range Weather Forecasting (ECMWF) forecast model are used in this paper.

Citation: DeSouza-Machado, S., Strow, L. L., Tangborn, A., Huang, X., Chen, X., Liu, X., Wu, W., and Yang, Q.: Single Footprint Retrievals for AIRS using a Fast TwoSlab Cloud-Representation Model and All-Sky Radiative Transfer Algorithm, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-261, in review, 2017.
Sergio DeSouza-Machado et al.
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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RC1: 'Review of amt-2017-261', Anonymous Referee #1, 26 Sep 2017 Printer-friendly Version 
AC1: 'Responses to Reviewer 1', S.G. DeSouza-Machado, 21 Nov 2017 Printer-friendly Version Supplement 
 
RC2: 'referee Comment on amt-2017-261', Anonymous Referee #2, 29 Sep 2017 Printer-friendly Version 
AC2: 'Response to Reviewer 2', S.G. DeSouza-Machado, 21 Nov 2017 Printer-friendly Version Supplement 
Sergio DeSouza-Machado et al.
Sergio DeSouza-Machado et al.

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Short summary
Thermodynamic fields retrieved from orbiting infrared sounders use a derived set of measurements as their starting point, rather than the actual observations. This leads to problems with noise and sampling. We have developed a fast accurate model with a simple vertical representation of clouds in the atmosphere for use in retrievals, which allows us to use all the actual low noise measurements at full resolution. These should eventually help produce more accurate weather forecasts.
Thermodynamic fields retrieved from orbiting infrared sounders use a derived set of...
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