Resonant absorption by water polymers in the atmosphere

Abstract

There is much evidence both from atmospheric^1–9 and laboratory^10,11 measurements that water vapour can show absorption of millimetre waves in addition to that predicted by models based on monomers¹² and dimers¹³. Constituents other than water can be eliminated as the cause of the extra absorption which is characterized by having a structured spectrum, increasing more rapidly with decreasing temperature than is expected from equilibrium phenomena and in the atmosphere showing a highly variable strength which is not simply correlated with total water content. The steep temperature dependence suggests invoking non-equilibrium water species to provide an explanation and this will account for variability as well as giving new prospects for understanding the spectral structure. A non-equilibrium model has, however, to be reconciled with what is known about supersaturation. It also opens the question of the nature of the energy source which is maintaining the steady state and allowing the extra absorption to be observed. I suggest here that water polymers containing about 50 molecules can, by collective acoustic resonances and postulated transition dipole moments, explain the observed component of absorption of millimetre waves by the atmosphere in some conditions. The polymers are metastable and are almost certainly the cause of supersaturation in cloud chambers but in these their lifetime is much greater than in the atmosphere.