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Volume 18, issue 20 | Copyright
Atmos. Chem. Phys., 18, 15231-15259, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 23 Oct 2018

Research article | 23 Oct 2018

Uncertainty of atmospheric microwave absorption model: impact on ground-based radiometer simulations and retrievals

Domenico Cimini1,2, Philip W. Rosenkranz3, Mikhail Y. Tretyakov4, Maksim A. Koshelev4, and Filomena Romano1 Domenico Cimini et al.
  • 1National Research Council of Italy, Institute of Methodologies for Environmental Analysis, Potenza, 85050, Italy
  • 2Center of Excellence CETEMPS, University of L'Aquila, L'Aquila, 67100, Italy
  • 3Massachusetts Institute of Technology, Cambridge, MA 02139, USA
  • 4Russian Academy of Sciences, Institute of Applied Physics, Nizhny Novgorod, 603950, Russia

Abstract. This paper presents a general approach to quantify absorption model uncertainty due to uncertainty in the underlying spectroscopic parameters. The approach is applied to a widely used microwave absorption model (Rosenkranz, 2017) and radiative transfer calculations in the 20–60GHz range, which are commonly exploited for atmospheric sounding by microwave radiometer (MWR). The approach, however, is not limited to any frequency range, observing geometry, or particular instrument. In the considered frequency range, relevant uncertainties come from water vapor and oxygen spectroscopic parameters. The uncertainty of the following parameters is found to dominate: (for water vapor) self- and foreign-continuum absorption coefficients, line broadening by dry air, line intensity, the temperature-dependence exponent for foreign-continuum absorption, and the line shift-to-broadening ratio; (for oxygen) line intensity, line broadening by dry air, line mixing, the temperature-dependence exponent for broadening, zero-frequency line broadening in air, and the temperature-dependence coefficient for line mixing. The full uncertainty covariance matrix is then computed for the set of spectroscopic parameters with significant impact. The impact of the spectroscopic parameter uncertainty covariance matrix on simulated downwelling microwave brightness temperatures (TB) in the 20–60GHz range is calculated for six atmospheric climatology conditions. The uncertainty contribution to simulated TB ranges from 0.30K (subarctic winter) to 0.92K (tropical) at 22.2GHz and from 2.73K (tropical) to 3.31K (subarctic winter) at 52.28GHz. The uncertainty contribution is nearly zero at 55–60GHz frequencies. Finally, the impact of spectroscopic parameter uncertainty on ground-based MWR retrievals of temperature and humidity profiles is discussed.

Publications Copernicus
Short summary
The paper presents a general approach to quantify the uncertainty related to atmospheric absorption models. These models describe how the atmosphere interacts with radiation, and they have general implications for atmospheric sciences. The presented approach contributes to a better understanding of the total uncertainty affecting atmospheric radiative properties, thus reducing the chances of systematic errors when observations are exploited for weather forecast or climate trend derivations.
The paper presents a general approach to quantify the uncertainty related to atmospheric...