Water Vapor Line Profile at 183-Ghz: Temperature Dependence of Broadening, Shifting, and Speed-Dependent Shape Parameters

M. A. Koshelev,I. N. Vilkov,D. S. Makarov,M. Yu Tretyakov,B. Vispoel,R. R. Gamache,D. Cimini,F. Romano,P. W. Rosenkranz

Journal of Quantitative Spectroscopy and Radiative Transfer（2021）SCI 3区

RAS | Univ Massachusetts Lowell | Inst Methodol Environm Anal | MIT

Cited 10|Views14

Abstract

The water vapor line at 183 GHz was studied over the temperature range of 219-358 K using a spectrometer with radioacoustic detection of absorption, providing a signal-to-noise ratio of up to 8000. The study includes the first measurement of speed-dependent collisional broadening and shifting of this line for both self- and air-broadening, and their temperature dependences. The sign of self-shifting changes at about 280 K. Line-shape parameters are obtained for Voigt and quadratic speed-dependent Voigt shape factors. Temperature dependences of the line parameters are analyzed using empirical models from the literature. Theoretical Modified Complex Robert-Bonamy calculations of the line shape parameters, their temperature and speed-dependence are made over the temperature range of 20 0-30 00 K. The measurements and calculations show very good agreement, although with some discrepancies for line shift parameters. The impact of the newly-measured line parameters on atmospheric water-vapor estimation from ground-based and satellite instruments is evaluated by simulation of downwelling and upwelling brightness temperatures and retrieved water-vapor mixing ratio, for atmospheric conditions typical of six climate zones. For the case of ground-based or limb-scanning radiometry with a background of cold space, the impact of speed-dependence is comparable to or exceeds that of measurement error and will introduce systematic errors if neglected. Therefore, consideration of speed-dependence is necessary for accurate estimation of water vapor with this line. The impact on upwelling brightness temperature is smaller. (C) 2020 Elsevier Ltd. All rights reserved.

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Key words

Microwave laboratory spectroscopy,Modified complex Robert-Bonamy calculations,Radiative transfer modeling,Speed-dependent profile,Water vapor,Line shape parameters

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