Article

The Water Vapour Continuum: Brief History and Recent Developments

V.E. Zuev Institute of Atmospheric Optics, SB RAS, 1, Academician Zuev Square, Tomsk, 634021 Russia
Surveys in Geophysics (Impact Factor: 4.13). 01/2014; 33(3-4):1-21. DOI: 10.1007/s10712-011-9170-y

ABSTRACT The water vapour continuum is characterised by absorption that varies smoothly with wavelength, from the visible to the microwave.
It is present within the rotational and vibrational–rotational bands of water vapour, which consist of large numbers of narrow
spectral lines, and in the many ‘windows’ between these bands. The continuum absorption in the window regions is of particular
importance for the Earth’s radiation budget and for remote-sensing techniques that exploit these windows. Historically, most
attention has focused on the 8–12μm (mid-infrared) atmospheric window, where the continuum is relatively well-characterised,
but there have been many fewer measurements within bands and in other window regions. In addition, the causes of the continuum
remain a subject of controversy. This paper provides a brief historical overview of the development of understanding of the
continuum and then reviews recent developments, with a focus on the near-infrared spectral region. Recent laboratory measurements
in near-infrared windows, which reveal absorption typically an order of magnitude stronger than in widely used continuum models,
are shown to have important consequences for remote-sensing techniques that use these windows for retrieving cloud properties.

KeywordsEarth radiation budget–Water vapour spectroscopy–Water dimers–Remote sensing

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