Articles | Volume 11, issue 4
https://doi.org/10.5194/amt-11-2159-2018
https://doi.org/10.5194/amt-11-2159-2018
Research article
 | 
16 Apr 2018
Research article |  | 16 Apr 2018

The water vapour self-continuum absorption in the infrared atmospheric windows: new laser measurements near 3.3 and 2.0 µm

Loic Lechevallier, Semen Vasilchenko, Roberto Grilli, Didier Mondelain, Daniele Romanini, and Alain Campargue

Abstract. The amplitude, the temperature dependence, and the physical origin of the water vapour absorption continuum are a long-standing issue in molecular spectroscopy with direct impact in atmospheric and planetary sciences. In recent years, we have determined the self-continuum absorption of water vapour at different spectral points of the atmospheric windows at 4.0, 2.1, 1.6, and 1.25 µm, by highly sensitive cavity-enhanced laser techniques. These accurate experimental constraints have been used to adjust the last version (3.2) of the semi-empirical MT_CKD model (Mlawer-Tobin_Clough-Kneizys-Davies), which is widely incorporated in atmospheric radiative-transfer codes. In the present work, the self-continuum cross-sections, CS, are newly determined at 3.3 µm (3007 cm−1) and 2.0 µm (5000 cm−1) by optical-feedback-cavity enhanced absorption spectroscopy (OFCEAS) and cavity ring-down spectroscopy (CRDS), respectively. These new data allow extending the spectral coverage of the 4.0 and 2.1 µm windows, respectively, and testing the recently released 3.2 version of the MT_CKD continuum. By considering high temperature literature data together with our data, the temperature dependence of the self-continuum is also obtained.

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Short summary
The amplitude, the temperature dependence, and the physical origin of the water vapour absorption continuum are a long standing issue in molecular spectroscopy with a direct impact in atmospheric and planetary sciences. Using highly sensitive laser spectrometers, the water self continuum has been determined with unprecedented sensitivity in infrared atmospheric transparency windows.