Contribution of water vapour dimers to clear sky absorption of solar radiation

Using recently derived-values of the water vapor dimer spectral absorption cross section we calculate the water vapor dimer contribution to the clear sky absorption of solar radiation. We consider the water dimer concentrations deduced from local equilibrium thermodynamics, and we account for the overlap of water vapor dimer and monomer absorption bands. We estimate that water vapor dimer contribution to the clear sky broad band column absorption of solar radiation is around 3 and 6 W/m2 for the cases of midlatitude summer and tropical atmosphere, respectively, at the solar zenith angle of 30°. For the cases of midlatitude winter, the US standard atmosphere and subarctic winter atmosphere, the dimer contribution to the absorption of solar radiation is less than 1 W/m2. Due to an uncertainty of the dimer's concentration within clouds, we are not able to deduce, at this time, the dimer absorption in a cloudy atmosphere.
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