Water vapour self-continuum in near-visible IR absorption bands: Measurements and semiempirical model of water dimer absorption

The nature of the water vapour continuum has been great scientific interest for more than 60 years. Here, self-continuum absorption spectra are retrieved at temperatures 398 K and 431 pressures from 1000 to 4155 mbar in 8800 10,600 cm−1 bands using high-resolution FTS measurements. For observed conditions, MT_CKD-3.2 model underestimates on average by 1.5–2 times. We use hypothesis that dimers contribute simulate experimentally-retrieved spectra, explain their characteristic temperature dependence spectral behaviour. values effective equilibrium constant derived temperatures. find dimer-based fits well measured this previous studies, but requires a higher compared modern estimates within range (268–431 K) region studied. It is shown likely responsible up 50% these bands. Possible causes incomplete explanation discussed. Extrapolating measurements atmospheric model, we newly-derived reduces calculated surface irradiances 0.016 W m−2 band overhead-Sun mid-latitude summer corresponding 12.5% enhancement radiative effect. change integrated across about 1%, with significant differences spectrally.