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Discussion papers
https://doi.org/10.5194/acp-2018-729
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-729
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 30 Oct 2018

Research article | 30 Oct 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Can downwelling far-infrared radiances over Antarctica be estimated from mid-infrared information?

Christophe Bellisario1, Helen E. Brindley2, Simon F. B. Tett1, Rolando Rizzi3, Gianluca Di Natale4, Luca Palchetti4, and Giovanni Bianchini4 Christophe Bellisario et al.
  • 1School of Geosciences, University of Edinburgh, Crew Building, The King's Buildings, Edinburgh EH9 3FF, UK
  • 2Space and Atmospheric Physics Group, National Centre for Earth Observation, Imperial College London, London, UK
  • 3Department of Physics and Astronomy, University of Bologna, Bologna, Italy
  • 4Istituto Nazionale di Ottica – CNR, Sesto Fiorentino, Italy

Abstract. Far-infrared (FIR: 100cm−1<wavenumber, ν<667cm−1) radiation emitted by the Earth and its atmosphere plays a key role in the Earth's energy budget. However, because of a lack of spectrally resolved measurements, radiation schemes in climate models suffer from a lack of constraint across this spectral range. Exploiting a method developed to estimate upwelling far-infrared radiation from mid-infrared (MIR: 667cm−1<ν<1400cm−1) observations, we explore the possibility of inferring zenith FIR downwelling radiances in zenith-looking observation geometry, focusing on clear-sky conditions in Antarctica. The methodology selects a MIR predictor wavenumber for each FIR wavenumber based on the maximum correlation seen between the different spectral ranges. Observations from the REFIR-PAD instrument (Radiation Explorer in the Far Infrared – Prototype for Application and Development) and high resolution radiance simulations generated from co-located radio soundings are used to develop and assess the method. We highlight the impact of noise on the correlation between MIR and FIR radiances by comparing the observational and theoretical cases. Using the observed values in isolation, between 150 and 360cm−1, differences between the true and extended radiances are less than 5%. However, in spectral bands of low signal, between 360 and 667cm−1, the impact of instrument noise is strong and increases the differences seen. When the extension of the observed spectra is performed using regression coefficients based on noise-free radiative-transfer simulations the results show strong biases, exceeding 100% where the signal is low. These biases are reduced to just a few percent if the noise in the observations is accounted for the simulation procedure. Our results imply that while it is feasible to use this type of approach to extend mid infrared spectral measurements to the far-infrared, the quality of the extension will be strongly dependent on the noise characteristics of the observations. A good knowledge of the atmospheric state associated with the measurements is also required in order to build a representative regression model.

Christophe Bellisario et al.
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Status: open (until 25 Dec 2018)
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Christophe Bellisario et al.
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Short summary
We explore the possibility of inferring far-infrared downwelling radiances from mid-infrared observations to better constrain radiation schemes in climate models. Our results imply that while it is feasible to use this type of approach, the quality of the extension will be strongly dependent on the noise characteristics of the observations and on the accurate characterisation of the atmospheric state.
We explore the possibility of inferring far-infrared downwelling radiances from mid-infrared...
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