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

Abstract

Th 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 selfcontinuum is also obtained.