Near‐infrared spectral measurements of liquid water absorption by clouds

Abstract

Spectral measurements of the solar flux in the near‐infrared region using an FTIR spectrometer have yielded important information concerning the absorption of solar radiation by clouds. A comparison of the spectra of solar fluxes for clear and overcast sky conditions measured from the ground for a northern mid‐latitude location demonstrates that about 118 W/m² of the solar radiation is absorbed preferentially by clouds in the 3,000–10,000 cm¹ region. The cloud radiative forcing ratio was estimated to be 1.24. Climate model calculations generally predict that clouds mainly scatter solar radiation while absorbing on average about 4% of the extraterrestrial insolation. The interaction of solar radiation with clouds may be dominated by the absorption of liquid water rather than by scattering, particularly if a sufficient number of liquid water droplets reside in the upper reaches of a cloud. This may contribute, in part, to the anomalous cloud absorption effect.